refactor(model-routing): centralize explicit foreground fallback policy (#6020)

* refactor(model-routing): centralize explicit foreground fallback policy

Make foreground fallback an explicit per-user, availability-only policy shared by streaming Chat, non-stream Chat, and Agent runs.

Preserve strict defaults, owner/model and credential boundaries, pinned Agent routes, and truthful per-round provenance/accounting. Carry provider-reported model identifiers through native streaming adapters, non-stream responses, and caches, and keep legacy default_model_fallbacks as tombstoned raw storage that generic settings APIs and agent tools cannot expose or mutate.

* fix(agent-loop): restore rebase-dropped qwen routing, workspace prompt, and temperature clamp

* fix(model-routing): thread selected endpoint identity, fix cost classification and fallback eligibility

* fix(chat): restore stream helpers and harden run stop lifecycle

* fix(model-routing): let numeric provider codes win over symbolic rate-limit statuses

* fix(agent-loop): apply qwen temperature and notes-tool clamps per fallback candidate

* fix(chat): honor queued stop across resend and reload canonical terminal on EOF

* fix(chat): track stop queue and cleanup ownership by per-send generation

* fix(agent-loop): preserve requested temperature for non-qwen fallback candidates

* fix(chat): reserve send ownership before any await and scope stop to the current send

* fix(chat): clear the previous run identity at send reservation

---------

Co-authored-by: RaresKeY <158580472+RaresKeY@users.noreply.github.com>
Co-authored-by: StressTestor <212606152+StressTestor@users.noreply.github.com>

core/database.py

@@ -1491,8 +1491,25 @@ def _migrate_assign_legacy_owner():
             with open(prefs_path, "r", encoding="utf-8") as f:
                 prefs = _json.load(f)
             if "_users" not in prefs and prefs:
-                # Flat format → nest under admin user
+                # Flat format → nest ordinary preferences under the admin
-                new_prefs = {"_users": {admin_user: prefs}}
+                # user. Foreground fallback is an explicit per-owner opt-in,
+                # so auth-disabled consent must remain inert at the flat root
+                # rather than becoming consent for the first named owner.
+                foreground_keys = {
+                    "foreground_fallback_enabled",
+                    "foreground_model_fallbacks",
+                }
+                named_prefs = {
+                    key: value
+                    for key, value in prefs.items()
+                    if key not in foreground_keys
+                }
+                new_prefs = {
+                    key: prefs[key]
+                    for key in foreground_keys
+                    if key in prefs
+                }
+                new_prefs["_users"] = {admin_user: named_prefs}
                 with open(prefs_path, "w", encoding="utf-8") as f:
                     _json.dump(new_prefs, f, indent=2)
                 logger.info(f"Migrated user_prefs.json to per-user format under '{admin_user}'")

mcp_servers/email_server.py

@@ -1802,7 +1802,6 @@ async def _ai_draft_reply_to_email(uid, folder="INBOX", reply_all=False, account
         from src.endpoint_resolver import (
             resolve_endpoint,
             resolve_utility_fallback_candidates,
-            resolve_chat_fallback_candidates,
         )
         from src.llm_core import llm_call_async_with_fallback
     except Exception as exc:
@@ -1843,13 +1842,6 @@ async def _ai_draft_reply_to_email(uid, folder="INBOX", reply_all=False, account
         utility_fallbacks = resolve_utility_fallback_candidates() or []
     for cand in utility_fallbacks:
         _add(*cand)
-    try:
-        chat_fallbacks = resolve_chat_fallback_candidates(owner=None) or []
-    except TypeError:
-        chat_fallbacks = resolve_chat_fallback_candidates() or []
-    for cand in chat_fallbacks:
-        _add(*cand)
-
     if not candidates:
         return {"error": "No LLM endpoint configured for AI reply"}
 

routes/auth_routes.py

@@ -22,6 +22,8 @@ from src.settings import (
     load_features as _load_features,
     save_features as _save_features,
     DEFAULT_SETTINGS,
+    RETIRED_SETTING_KEYS,
+    without_retired_settings,
 )
 from src.integrations import (
     load_integrations,
@@ -689,7 +691,7 @@ def setup_auth_routes(auth_manager: AuthManager) -> APIRouter:
         a scrubbed copy with secret keys blanked. The frontend uses this
         for keybinds + TTS prefs, so it stays callable without admin."""
         user = _get_current_user(request)
-        settings = _load_settings()
+        settings = without_retired_settings(_load_settings())
         if user and auth_manager.is_admin(user):
             return settings
         return scrub_settings(settings)
@@ -709,6 +711,8 @@ def setup_auth_routes(auth_manager: AuthManager) -> APIRouter:
             "agent_max_tool_calls": (0, 1000),  # 0 = unlimited
         }
         for key in DEFAULT_SETTINGS:
+            if key in RETIRED_SETTING_KEYS:
+                continue
             if key not in body:
                 continue
             val = body[key]
@@ -721,7 +725,7 @@ def setup_auth_routes(auth_manager: AuthManager) -> APIRouter:
                 val = max(lo, min(val, hi))
             current[key] = val
         _save_settings(current)
-        return current
+        return without_retired_settings(current)
 
     # ---- Integrations CRUD ----
 

routes/chat_helpers.py

@@ -15,7 +15,7 @@ from core.database import Session as DBSession, ModelEndpoint
 from src.llm_core import normalize_model_id
 from src.endpoint_resolver import normalize_base
 from src.context_compactor import maybe_compact, trim_for_context
-from src.model_context import estimate_tokens
+from src.model_context import estimate_tokens, get_context_length
 from src.auth_helpers import effective_user
 from src.prompt_security import untrusted_context_message
 from src.attachment_refs import attachment_ref
@@ -152,10 +152,38 @@ class ChatContext:
     # Uploads attached to this user turn, resolved and owner-checked for the
     # agent's private context. This is not emitted to the browser.
     uploaded_files: list = field(default_factory=list)
+    # Route-neutral prompt before any model-window compaction/trimming. This is
+    # retained only when explicit foreground fallbacks are enabled so each
+    # concrete candidate can apply its own context budget independently.
+    route_messages: list = field(default_factory=list)
 
 
 # ── Helpers ────────────────────────────────────────────────────────────── #
 
+def _allowed_models_from_privileges(privs: dict) -> Optional[frozenset[str]]:
+    if privs.get("block_all_models"):
+        return frozenset()
+    allowed_raw = privs.get("allowed_models")
+    allowed = allowed_raw if isinstance(allowed_raw, list) else []
+    restricted = bool(privs.get("allowed_models_restricted")) or bool(allowed)
+    return frozenset(model for model in allowed if isinstance(model, str)) if restricted else None
+
+
+def _allowed_models_for_request(request) -> Optional[frozenset[str]]:
+    """Return the caller's model allowlist, or ``None`` when unrestricted."""
+
+    try:
+        user = effective_user(request)
+    except Exception:
+        user = None
+    if not user:
+        return None
+    auth_manager = getattr(getattr(request.app, "state", None), "auth_manager", None)
+    if not auth_manager:
+        return None
+    privs = auth_manager.get_privileges(user) or {}
+    return _allowed_models_from_privileges(privs)
+
 def _enforce_chat_privileges(request, sess) -> None:
     """Apply the per-user privilege gates (allowed_models + max_messages_per_day)
     that both /api/chat and /api/chat_stream must enforce BEFORE any LLM work.
@@ -185,10 +213,8 @@ def _enforce_chat_privileges(request, sess) -> None:
     if privs.get("block_all_models"):
         raise HTTPException(403, f"Your account is not allowed to use model '{sess.model}'.")
 
-    allowed_raw = privs.get("allowed_models")
+    allowed_models = _allowed_models_from_privileges(privs)
-    allowed = allowed_raw if isinstance(allowed_raw, list) else []
+    if allowed_models is not None and sess.model and sess.model not in allowed_models:
-    restricted = bool(privs.get("allowed_models_restricted")) or bool(allowed)
-    if restricted and sess.model and sess.model not in allowed:
         raise HTTPException(403, f"Your account is not allowed to use model '{sess.model}'.")
 
     cap = int(privs.get("max_messages_per_day") or 0)
@@ -287,96 +313,6 @@ async def auto_name_session(session_manager, sess):
         logger.error(f"Auto-name failed for {sess.id}: {e}\n{traceback.format_exc()}")
 
 
-def try_fallback_endpoint(sess, session_id: str) -> dict | None:
-    """Find an alternative working endpoint when the current one fails.
-
-    Returns {"model": ..., "endpoint_url": ..., "endpoint_name": ...} or None.
-    """
-    import requests as _req
-    from src.endpoint_resolver import (
-        build_chat_url,
-        build_headers,
-        build_models_url,
-        normalize_base,
-        resolve_endpoint_runtime,
-    )
-    from src.chatgpt_subscription import is_chatgpt_subscription_base
-
-    current_url = sess.endpoint_url or ""
-    owner = getattr(sess, "owner", None)
-    db = SessionLocal()
-    try:
-        q = db.query(ModelEndpoint).filter(
-            ModelEndpoint.is_enabled == True
-        )
-        if owner:
-            from src.auth_helpers import owner_filter
-            q = owner_filter(q, ModelEndpoint, owner)
-        endpoints = q.all()
-    finally:
-        db.close()
-
-    for ep in endpoints:
-        base = normalize_base(ep.base_url)
-        # Skip current endpoint
-        if current_url and base in current_url:
-            continue
-        try:
-            base, api_key = resolve_endpoint_runtime(ep, owner=owner)
-        except Exception:
-            continue
-        ping_url = build_models_url(base)
-        headers = build_headers(api_key, base)
-        try:
-            if ping_url:
-                r = _req.get(ping_url, headers=headers, timeout=5)
-                r.raise_for_status()
-                data = r.json()
-                models = [m.get("id") for m in (data.get("data") or []) if m.get("id")]
-                if not models:
-                    models = [
-                        m.get("name") or m.get("model")
-                        for m in (data.get("models") or [])
-                        if m.get("name") or m.get("model")
-                    ]
-            else:
-                models = json.loads(ep.cached_models or "[]")
-            if not models:
-                continue
-            # Found a working endpoint — update session
-            new_model = models[0]
-            chat_url = build_chat_url(base)
-            new_headers = build_headers(api_key, base)
-            persisted_headers = {} if is_chatgpt_subscription_base(base) else new_headers
-
-            sess.model = new_model
-            sess.endpoint_url = chat_url
-            sess.headers = new_headers
-
-            # Persist
-            _db = SessionLocal()
-            try:
-                _db.query(DBSession).filter(DBSession.id == session_id).update({
-                    "model": new_model,
-                    "endpoint_url": chat_url,
-                    "headers": persisted_headers,
-                })
-                _db.commit()
-            finally:
-                _db.close()
-
-            logger.info(f"Fallback: switched session {session_id} from {current_url} to {ep.name} ({new_model})")
-            return {
-                "model": new_model,
-                "endpoint_url": chat_url,
-                "endpoint_name": ep.name,
-            }
-        except Exception:
-            continue
-
-    return None
-
-
 def extract_preset(chat_handler, preset_id) -> PresetInfo:
     """Extract preset parameters via chat_handler."""
     temperature, max_tokens, system_prompt, char_name = (
@@ -687,6 +623,7 @@ async def build_chat_context(
     use_enhanced_message: bool = False,
     agent_mode: bool = False,
     allow_tool_preprocessing: bool = True,
+    defer_context_shaping: bool = False,
 ) -> ChatContext:
     """Build the full context (preface + messages) for an LLM call.
 
@@ -830,12 +767,21 @@ async def build_chat_context(
         except Exception:
             logger.debug("Failed to add current date/time context", exc_info=True)
 
-    # Auto-compact
+    route_messages = list(messages)
+    # Explicit fallback routing must shape from the same route-neutral prompt
+    # for every candidate. Running selected-model compaction here would mutate
+    # session history before we know which route can answer and would make a
+    # later larger-context candidate unable to recover discarded history.
+    if defer_context_shaping:
+        context_length = get_context_length(sess.endpoint_url, sess.model)
+        was_compacted = False
+    else:
         messages, context_length, was_compacted = await maybe_compact(
             sess, sess.endpoint_url, sess.model, messages, sess.headers, owner=user,
         )
     _before_trim_messages = len(messages)
     _before_trim_tokens = estimate_tokens(messages)
+    if not defer_context_shaping:
         messages = trim_for_context(messages, context_length)
     _after_trim_messages = len(messages)
     _after_trim_tokens = estimate_tokens(messages)
@@ -860,6 +806,7 @@ async def build_chat_context(
         context_tokens_after_trim=_after_trim_tokens,
         auto_opened_docs=auto_opened_docs,
         uploaded_files=uploaded_files,
+        route_messages=route_messages,
     )
 
 

routes/chat_routes.py

@@ -15,13 +15,28 @@ from pydantic import ValidationError
 
 from core.models import ChatMessage
 from src.request_models import ChatRequest
-from src.llm_core import llm_call_async, stream_llm, stream_llm_with_fallback
+from src.llm_core import (
+    _normalize_http_status,
+    llm_call_async,
+    llm_call_async_with_route_fallback,
+    stream_llm,
+    stream_llm_with_fallback,
+)
 from src.agent_loop import stream_agent_loop
 from src import agent_runs
 from src.model_context import estimate_tokens
+from src.context_compactor import (
+    apply_compaction_state,
+    maybe_compact,
+    trim_for_context,
+)
 from src.chat_helpers import coerce_message_and_session
 from src.endpoint_resolver import normalize_base as _normalize_base, build_chat_url
-from src.foreground_model_routing import build_foreground_model_candidates
+from src.foreground_model_routing import (
+    build_foreground_model_candidates,
+    build_foreground_route_descriptors,
+    resolve_foreground_model_policy,
+)
 from src.session_search import search_session_messages
 from src.prompt_security import untrusted_context_message
 from core.exceptions import SessionNotFoundError
@@ -39,7 +54,9 @@ from routes.chat_helpers import (
     build_chat_context,
     save_assistant_response,
     run_post_response_tasks,
+    accumulate_token_usage,
     clean_thinking_for_save,
+    _allowed_models_for_request,
     _enforce_chat_privileges,
 )
 from src.action_intents import ToolIntent, classify_tool_intent as _classify_tool_intent
@@ -57,6 +74,74 @@ logger = logging.getLogger(__name__)
 _active_streams: Dict[str, dict] = {}
 
 
+def _stream_failure_status(chunk: str) -> Optional[int]:
+    """Extract a provider status without retaining provider-supplied detail."""
+
+    try:
+        for line in str(chunk or "").splitlines():
+            if not line.startswith("data: "):
+                continue
+            status = json.loads(line[6:]).get("status")
+            return _normalize_http_status(status)
+    except json.JSONDecodeError:
+        return None
+    return None
+
+
+def _chat_candidate_request_factory(
+    messages,
+    fallback_context_length: int = 0,
+    *,
+    session=None,
+    owner: Optional[str] = None,
+):
+    """Shape one route-neutral Chat prompt for each candidate window."""
+
+    state = {
+        "requests": {},
+        "context_lengths": {},
+        "trim_stats": {},
+        "compactions": {},
+        "was_compacted": {},
+    }
+
+    async def factory(index, candidate_url, candidate_model, candidate_headers):
+        compaction_state = {}
+        candidate_messages, context_length, was_compacted = await maybe_compact(
+            session,
+            candidate_url,
+            candidate_model,
+            list(messages),
+            candidate_headers,
+            owner=owner,
+            persist=False,
+            compaction_state=compaction_state,
+        )
+        if not context_length:
+            context_length = fallback_context_length
+        request_messages = trim_for_context(candidate_messages, context_length)
+        state["requests"][index] = request_messages
+        state["context_lengths"][index] = context_length
+        state["compactions"][index] = compaction_state
+        state["was_compacted"][index] = was_compacted
+        state["trim_stats"][index] = {
+            "messages_before": len(messages),
+            "messages_after": len(request_messages),
+            "tokens_before": estimate_tokens(messages),
+            "tokens_after": estimate_tokens(request_messages),
+        }
+        return {"messages": request_messages}
+
+    return factory, state
+
+
+def _candidate_index(candidates, actual_candidate) -> int:
+    for index, candidate in enumerate(candidates):
+        if candidate == actual_candidate:
+            return index
+    return 0
+
+
 def _stream_set(session_id: str, **fields) -> None:
     """Update fields on the active-stream entry for `session_id`, or
     no-op if the entry has already been popped. Using .get() avoids a
@@ -590,8 +675,8 @@ def setup_chat_routes(
     # ------------------------------------------------------------------ #
     # POST /api/chat (non-streaming)
     # ------------------------------------------------------------------ #
-    @router.post("/api/chat", response_model=Dict[str, str])
+    @router.post("/api/chat", response_model=Dict[str, Any])
-    async def chat_endpoint(request: Request, chat_request: ChatRequest) -> Dict[str, str]:
+    async def chat_endpoint(request: Request, chat_request: ChatRequest) -> Dict[str, Any]:
         _set_user_time_from_request(request)
 
         message = chat_request.message
@@ -623,6 +708,8 @@ def setup_chat_routes(
                 400,
                 "No model selected for this chat. Open the model picker and choose one before sending.",
             )
+        if not (getattr(sess, "endpoint_url", "") or "").strip():
+            raise HTTPException(400, "Selected model endpoint is not configured")
 
         # Same allowed_models + daily-cap gate as chat_stream (mirror so the
         # non-streaming path can't be used to bypass).
@@ -638,6 +725,11 @@ def setup_chat_routes(
         if memory_response:
             return {"response": memory_response}
 
+        foreground_policy = resolve_foreground_model_policy(
+            owner=owner,
+            allowed_models=_allowed_models_for_request(request),
+        )
+
         # Build shared context (preset, preprocess, preface, compact)
         ctx = await build_chat_context(
             sess, request, chat_handler, chat_processor,
@@ -649,6 +741,7 @@ def setup_chat_routes(
             time_filter=time_filter,
             webhook_manager=webhook_manager,
             allow_tool_preprocessing=allow_tool_preprocessing,
+            defer_context_shaping=foreground_policy.enabled,
         )
 
         # Research injection
@@ -662,24 +755,88 @@ def setup_chat_routes(
                 research_ctx = await research_handler.call_research_service(
                     message, _r_ep, _r_model, llm_headers=_r_headers
                 )
-                ctx.messages.insert(
+                research_message = untrusted_context_message("research context", research_ctx)
+                ctx.messages.insert(len(ctx.preface), research_message)
+                if foreground_policy.enabled:
+                    getattr(ctx, "route_messages", ctx.messages).insert(
                         len(ctx.preface),
-                    untrusted_context_message("research context", research_ctx),
+                        research_message,
                     )
             except Exception as e:
                 logger.error(f"Research failed: {e}")
 
-        reply = await llm_call_async(
+        foreground_candidates = build_foreground_model_candidates(
             sess.endpoint_url,
             sess.model,
-            ctx.messages,
+            sess.headers,
-            headers=sess.headers,
+            owner=owner,
+            policy=foreground_policy,
+        )
+        route_descriptors = build_foreground_route_descriptors(
+            sess.endpoint_url,
+            sess.model,
+            sess.headers,
+            owner=owner,
+            policy=foreground_policy,
+            selected_endpoint_id=chat_request.selected_endpoint_id,
+        )
+        candidate_request_factory = None
+        selected_context_length = getattr(ctx, "context_length", 0)
+        candidate_request_state = {
+            "context_lengths": {0: selected_context_length},
+            "requests": {0: ctx.messages},
+            "trim_stats": {},
+        }
+        request_messages = ctx.messages
+        if foreground_policy.enabled:
+            request_messages = getattr(ctx, "route_messages", ctx.messages)
+            candidate_request_factory, candidate_request_state = _chat_candidate_request_factory(
+                request_messages,
+                selected_context_length,
+                session=sess,
+                owner=owner,
+            )
+        requested_model = sess.model
+        reply, actual_candidate, actual_model = await llm_call_async_with_route_fallback(
+            foreground_candidates,
+            request_messages,
+            fallback_statuses=foreground_policy.eligible_statuses,
+            candidate_request_factory=candidate_request_factory,
             temperature=ctx.preset.temperature,
             max_tokens=ctx.preset.max_tokens,
             prompt_type=preset_id,
             session_id=session,
         )
-        _clean_reply, _clean_md = clean_thinking_for_save(reply, {"model": sess.model})
+        actual_index = _candidate_index(foreground_candidates, actual_candidate)
+        apply_compaction_state(
+            sess,
+            candidate_request_state.get("compactions", {}).get(actual_index),
+        )
+        requested_route = route_descriptors[0]
+        actual_route = route_descriptors[actual_index]
+        actual_trim = candidate_request_state.get("trim_stats", {}).get(actual_index, {})
+        _clean_reply, _clean_md = clean_thinking_for_save(
+            reply,
+            {
+                "model": actual_model,
+                "requested_model": requested_model,
+                "endpoint_id": actual_route.get("endpoint_id"),
+                "endpoint_label": actual_route.get("endpoint_label"),
+                "requested_endpoint_id": requested_route.get("endpoint_id"),
+                "requested_endpoint_label": requested_route.get("endpoint_label"),
+                "context_length": candidate_request_state["context_lengths"].get(
+                    actual_index,
+                    selected_context_length,
+                ),
+                "context_trimmed": bool(
+                    actual_trim
+                    and (
+                        actual_trim.get("messages_after") < actual_trim.get("messages_before")
+                        or actual_trim.get("tokens_after") < actual_trim.get("tokens_before")
+                    )
+                ),
+            },
+        )
         sess.add_message(ChatMessage("assistant", _clean_reply, metadata=_clean_md))
 
         from core.database import update_session_last_accessed
@@ -695,7 +852,15 @@ def setup_chat_routes(
             allow_background_extraction=not tool_policy.block_all_tool_calls,
         )
 
-        return {"response": reply}
+        return {
+            "response": reply,
+            "requested_model": requested_model,
+            "model": actual_model,
+            "requested_endpoint_id": requested_route.get("endpoint_id"),
+            "requested_endpoint_label": requested_route.get("endpoint_label"),
+            "endpoint_id": actual_route.get("endpoint_id"),
+            "endpoint_label": actual_route.get("endpoint_label"),
+        }
 
     # ------------------------------------------------------------------ #
     # POST /api/chat_stream
@@ -724,6 +889,11 @@ def setup_chat_routes(
         use_research = form_data.get("use_research")
         time_filter = form_data.get("time_filter")
         preset_id = form_data.get("preset_id")
+        selected_endpoint_id = str(
+            form_data.get("selected_endpoint_id")
+            or (body or {}).get("selected_endpoint_id")
+            or ""
+        ).strip()
         # Issue #3229: API callers send JSON, not FormData.  Read from the
         # JSON body as fallback so callers who send {"allow_bash": true}
         # actually get bash enabled.
@@ -896,6 +1066,8 @@ def setup_chat_routes(
                     400,
                     "No model selected for this chat. Open the model picker and choose one before sending.",
                 )
+            if not (getattr(sess, "endpoint_url", "") or "").strip():
+                raise HTTPException(400, "Selected model endpoint is not configured")
             if (
                 chat_mode == "chat"
                 and isinstance(message, str)
@@ -971,6 +1143,10 @@ def setup_chat_routes(
             last_user_message=message,
         )
         allow_tool_preprocessing = not pre_context_tool_policy.block_all_tool_calls
+        foreground_policy = resolve_foreground_model_policy(
+            owner=owner,
+            allowed_models=_allowed_models_for_request(request),
+        )
 
         # Build shared context (stream path uses enhanced_message for context preface)
         ctx = await build_chat_context(
@@ -993,6 +1169,7 @@ def setup_chat_routes(
             # index would be useless / unwanted noise.
             agent_mode=(chat_mode == "agent"),
             allow_tool_preprocessing=allow_tool_preprocessing,
+            defer_context_shaping=foreground_policy.enabled,
         )
 
         _research_flags = {"do": do_research}  # Mutable container for generator scope
@@ -1292,6 +1469,8 @@ def setup_chat_routes(
                         "what aspects matter most, are they comparing to something, what's their context "
                         "(moving, traveling, curiosity). Be conversational. Keep it short."
                     })
+                    if foreground_policy.enabled:
+                        getattr(ctx, "route_messages", ctx.messages).insert(0, dict(ctx.messages[0]))
                     _skip_research = True
                 else:
                     _skip_research = False
@@ -1388,7 +1567,12 @@ def setup_chat_routes(
                     _active_streams.pop(session, None)
                     return
 
-            messages = _ensure_current_request_is_latest_user(ctx.messages, message)
+            context_source = (
+                getattr(ctx, "route_messages", ctx.messages)
+                if foreground_policy.enabled
+                else ctx.messages
+            )
+            messages = _ensure_current_request_is_latest_user(context_source, message)
 
             # Auto-compact notification
             if ctx.was_compacted:
@@ -1400,25 +1584,56 @@ def setup_chat_routes(
             thinking_response = ""
             last_metrics = None
 
-            # Foreground Chat and Agent requests use one owner-aware policy
+            # Foreground Chat and Agent requests share one explicit owner-aware
-            # boundary. Legacy `default_model_fallbacks` data is not eligible.
+            # policy. Strict mode is the default; legacy values are unrelated.
+            _foreground_policy = foreground_policy
             _foreground_candidates = build_foreground_model_candidates(
                 sess.endpoint_url,
                 sess.model,
                 sess.headers,
                 owner=_user,
+                policy=_foreground_policy,
+            )
+            _foreground_route_descriptors = build_foreground_route_descriptors(
+                sess.endpoint_url,
+                sess.model,
+                sess.headers,
+                owner=_user,
+                policy=_foreground_policy,
+                selected_endpoint_id=selected_endpoint_id,
+            )
+            _chat_request_factory = None
+            _selected_context_length = getattr(ctx, "context_length", 0)
+            _chat_request_state = {
+                "context_lengths": {0: _selected_context_length},
+                "requests": {0: messages},
+                "trim_stats": {},
+            }
+            if _foreground_policy.enabled:
+                _chat_request_factory, _chat_request_state = _chat_candidate_request_factory(
+                    messages,
+                    _selected_context_length,
+                    session=sess,
+                    owner=_user,
                 )
 
             # Send model name early so the frontend can show it during streaming
             _model_suffix = "Research" if effective_do_research else None
-            _model_info = {"type": "model_info", "model": sess.model}
+            _selected_route = _foreground_route_descriptors[0]
+            _model_info = {
+                "type": "model_info",
+                "model": sess.model,
+                "endpoint_id": _selected_route.get("endpoint_id"),
+                "endpoint_label": _selected_route.get("endpoint_label"),
+            }
             if _model_suffix:
                 _model_info["suffix"] = _model_suffix
             if ctx.preset.character_name:
                 _model_info["character_name"] = ctx.preset.character_name
             yield f'data: {json.dumps(_model_info)}\n\n'
 
-            if image_generation_session:
+            _terminal_saved = False
+            if _is_image_generation_session(sess, owner=_user):
                 from src.settings import get_setting
                 if tool_policy.blocks("generate_image"):
                     _blocked_msg = tool_policy.reason_for("generate_image")
@@ -1521,6 +1736,16 @@ def setup_chat_routes(
                 _answered_by = None  # set if the selected model failed and a fallback answered
                 _requested_model = sess.model
                 _actual_model = None
+                _requested_route = _foreground_route_descriptors[0]
+                _actual_route = _requested_route
+                _actual_candidate_index = 0
+                _chat_terminal_saved = False
+                def _commit_chat_compaction(candidate_index: int) -> bool:
+                    return apply_compaction_state(
+                        sess,
+                        _chat_request_state.get("compactions", {}).get(candidate_index),
+                    )
+
                 # ── Chat mode: call stream_llm directly, NO tools, NO document access ──
                 try:
                     async for chunk in stream_llm_with_fallback(
@@ -1536,11 +1761,21 @@ def setup_chat_routes(
                         prompt_type=preset_id,
                         tools=None,
                         session_id=session,
+                        fallback_statuses=_foreground_policy.eligible_statuses,
+                        fallback_on_empty=_foreground_policy.fallback_on_empty,
+                        candidate_request_factory=_chat_request_factory,
+                        candidate_route_descriptors=_foreground_route_descriptors,
                     ):
                         if chunk.startswith("data: ") and not chunk.startswith("data: [DONE]"):
                             try:
                                 data = json.loads(chunk[6:])
                                 if "delta" in data:
+                                    if _commit_chat_compaction(_actual_candidate_index):
+                                        _compacted_length = _chat_request_state["context_lengths"].get(
+                                            _actual_candidate_index,
+                                            _selected_context_length,
+                                        )
+                                        yield f'data: {json.dumps({"type": "compacted", "context_length": _compacted_length})}\n\n'
                                     # Reasoning tokens arrive flagged thinking:true.
                                     # Forward them so the client can show a thinking
                                     # indicator, but don't fold them into the saved
@@ -1556,29 +1791,82 @@ def setup_chat_routes(
                                     # Forward the notice and remember the real model.
                                     _answered_by = data.get("answered_by") or _answered_by
                                     _actual_model = _actual_model or _answered_by
+                                    _actual_candidate_index = data.get("candidate_index", 0)
+                                    if not isinstance(_actual_candidate_index, int):
+                                        _actual_candidate_index = 0
+                                    if 0 <= _actual_candidate_index < len(_foreground_route_descriptors):
+                                        _actual_route = _foreground_route_descriptors[_actual_candidate_index]
+                                    if _commit_chat_compaction(_actual_candidate_index):
+                                        _compacted_length = _chat_request_state["context_lengths"].get(
+                                            _actual_candidate_index,
+                                            _selected_context_length,
+                                        )
+                                        yield f'data: {json.dumps({"type": "compacted", "context_length": _compacted_length})}\n\n'
                                     data["selected_model"] = data.get("selected_model") or _requested_model
-                                    yield chunk
+                                    yield f'data: {json.dumps(data)}\n\n'
                                 elif data.get("type") == "model_actual":
+                                    if _commit_chat_compaction(_actual_candidate_index):
+                                        _compacted_length = _chat_request_state["context_lengths"].get(
+                                            _actual_candidate_index,
+                                            _selected_context_length,
+                                        )
+                                        yield f'data: {json.dumps({"type": "compacted", "context_length": _compacted_length})}\n\n'
                                     _actual_model = data.get("model") or _actual_model
                                     data["requested_model"] = _requested_model
+                                    data["requested_endpoint_id"] = _requested_route.get("endpoint_id")
+                                    data["requested_endpoint_label"] = _requested_route.get("endpoint_label")
+                                    data["endpoint_id"] = _actual_route.get("endpoint_id")
+                                    data["endpoint_label"] = _actual_route.get("endpoint_label")
                                     yield f'data: {json.dumps(data)}\n\n'
                                 elif data.get("type") == "usage":
+                                    if _commit_chat_compaction(_actual_candidate_index):
+                                        _compacted_length = _chat_request_state["context_lengths"].get(
+                                            _actual_candidate_index,
+                                            _selected_context_length,
+                                        )
+                                        yield f'data: {json.dumps({"type": "compacted", "context_length": _compacted_length})}\n\n'
                                     last_metrics = data.get("data", {})
                                     _reported_model = last_metrics.get("model")
                                     last_metrics["requested_model"] = _requested_model
                                     last_metrics["model"] = _reported_model or _actual_model or _answered_by or _requested_model
-                                    if ctx.context_trimmed:
+                                    last_metrics["requested_endpoint_id"] = _requested_route.get("endpoint_id")
+                                    last_metrics["requested_endpoint_label"] = _requested_route.get("endpoint_label")
+                                    last_metrics["endpoint_id"] = _actual_route.get("endpoint_id")
+                                    last_metrics["endpoint_label"] = _actual_route.get("endpoint_label")
+                                    if isinstance(
+                                        _actual_route.get("endpoint_cost_tracked"),
+                                        bool,
+                                    ):
+                                        last_metrics["endpoint_cost_tracked"] = _actual_route.get(
+                                            "endpoint_cost_tracked"
+                                        )
+                                    _actual_context_length = _chat_request_state["context_lengths"].get(
+                                    _actual_candidate_index,
+                                        _selected_context_length,
+                                    )
+                                    _route_trim = _chat_request_state.get("trim_stats", {}).get(
+                                        _actual_candidate_index,
+                                        {},
+                                    )
+                                    if _route_trim and (
+                                        _route_trim.get("messages_after") < _route_trim.get("messages_before")
+                                        or _route_trim.get("tokens_after") < _route_trim.get("tokens_before")
+                                    ):
+                                        last_metrics["context_trimmed"] = True
+                                        last_metrics["context_messages_before_trim"] = _route_trim.get("messages_before")
+                                        last_metrics["context_messages_after_trim"] = _route_trim.get("messages_after")
+                                        last_metrics["context_tokens_before_trim"] = _route_trim.get("tokens_before")
+                                        last_metrics["context_tokens_after_trim"] = _route_trim.get("tokens_after")
+                                    elif ctx.context_trimmed:
                                         last_metrics["context_trimmed"] = True
                                         last_metrics["context_messages_before_trim"] = ctx.context_messages_before_trim
                                         last_metrics["context_messages_after_trim"] = ctx.context_messages_after_trim
                                         last_metrics["context_tokens_before_trim"] = ctx.context_tokens_before_trim
                                         last_metrics["context_tokens_after_trim"] = ctx.context_tokens_after_trim
-                                    request_context_tokens = ctx.context_tokens_after_trim or estimate_tokens(messages)
+                                    if _actual_context_length and last_metrics.get("input_tokens"):
-                                    last_metrics["request_context_tokens"] = request_context_tokens
+                                        pct = min(round((last_metrics["input_tokens"] / _actual_context_length) * 100, 1), 100.0)
-                                    if ctx.context_length and request_context_tokens:
-                                        pct = min(round((request_context_tokens / ctx.context_length) * 100, 1), 100.0)
                                         last_metrics["context_percent"] = pct
-                                        last_metrics["context_length"] = ctx.context_length
+                                        last_metrics["context_length"] = _actual_context_length
                                     # The frontend reads `tokens_per_second`; the raw usage event
                                     # carries the backend's true gen speed as `gen_tps` (llama.cpp
                                     # timings). Map it through so this direct-chat path shows real
@@ -1593,17 +1881,121 @@ def setup_chat_routes(
                                 yield chunk
                         elif chunk.startswith("event: error"):
                             logger.warning(f"Stream error for {sess.model} on {sess.endpoint_url}: {chunk!r}")
+                            if (
+                                not _chat_terminal_saved
+                                and (full_response.strip() or thinking_response.strip())
+                            ):
+                                _failure_status = _stream_failure_status(chunk)
+                                _failure_message = (
+                                    f"Model request failed (HTTP {_failure_status})"
+                                    if _failure_status is not None
+                                    else "Model request failed"
+                                )
+                                _terminal_content = full_response.strip()
+                                _failure_note = f"[Response stopped: {_failure_message}]"
+                                _terminal_content = (
+                                    f"{_terminal_content}\n\n{_failure_note}"
+                                    if _terminal_content
+                                    else _failure_note
+                                )
+                                _had_terminal_usage = bool(last_metrics)
+                                _terminal_metrics = dict(last_metrics or {})
+                                if not _had_terminal_usage:
+                                    _actual_request_messages = _chat_request_state["requests"].get(
+                                        _actual_candidate_index,
+                                        messages,
+                                    )
+                                    _actual_context_length = _chat_request_state["context_lengths"].get(
+                                        _actual_candidate_index,
+                                        _selected_context_length,
+                                    )
+                                    _estimated_input = estimate_tokens(_actual_request_messages)
+                                    _estimated_output = max(
+                                        len(full_response + thinking_response) // 4,
+                                        0,
+                                    )
+                                    _terminal_metrics.update({
+                                        "input_tokens": _estimated_input,
+                                        "output_tokens": _estimated_output,
+                                        "total_tokens": _estimated_input + _estimated_output,
+                                        "usage_source": "estimated",
+                                        "response_time": round(time.time() - _chat_start, 2),
+                                        "context_length": _actual_context_length,
+                                        "context_percent": (
+                                            min(
+                                                round(
+                                                    (_estimated_input / _actual_context_length) * 100,
+                                                    1,
+                                                ),
+                                                100.0,
+                                            )
+                                            if _actual_context_length
+                                            else 0
+                                        ),
+                                    })
+                                _terminal_metrics.update({
+                                    "failed": True,
+                                    "failure": {
+                                        "status": _failure_status,
+                                        "message": _failure_message,
+                                    },
+                                    "model": _actual_model or _answered_by or _requested_model,
+                                    "requested_model": _requested_model,
+                                    "endpoint_id": _actual_route.get("endpoint_id"),
+                                    "endpoint_label": _actual_route.get("endpoint_label"),
+                                    "requested_endpoint_id": _requested_route.get("endpoint_id"),
+                                    "requested_endpoint_label": _requested_route.get("endpoint_label"),
+                                })
+                                if isinstance(
+                                    _actual_route.get("endpoint_cost_tracked"),
+                                    bool,
+                                ):
+                                    _terminal_metrics["endpoint_cost_tracked"] = _actual_route.get(
+                                        "endpoint_cost_tracked"
+                                    )
+                                if thinking_response.strip():
+                                    _terminal_metrics["thinking"] = thinking_response.strip()
+                                _commit_chat_compaction(_actual_candidate_index)
+                                _saved_id = save_assistant_response(
+                                    sess,
+                                    session_manager,
+                                    session,
+                                    _terminal_content,
+                                    _terminal_metrics,
+                                    character_name=ctx.preset.character_name,
+                                    incognito=incognito,
+                                )
+                                accumulate_token_usage(session, _terminal_metrics)
+                                _chat_terminal_saved = True
+                                _stream_set(session, status="error")
+                                if _saved_id:
+                                    yield f'data: {json.dumps({"type": "message_saved", "id": _saved_id})}\n\n'
+                                yield f'data: {json.dumps({"type": "chat_terminal", "data": _terminal_metrics})}\n\n'
                             yield chunk
                         elif chunk.startswith("event: "):
                             yield chunk
                         elif chunk == "data: [DONE]\n\n":
+                            if _chat_terminal_saved:
+                                # Some providers append DONE after a terminal
+                                # error.  The failed partial is already saved;
+                                # never re-save/post-process it as a success or
+                                # advertise successful completion to the client.
+                                continue
                             # Generate fallback metrics if LLM didn't send usage
                             if not last_metrics and full_response:
                                 _elapsed = time.time() - _chat_start
-                                _est_in = estimate_tokens(messages)
                                 _est_out = len(full_response) // 4
                                 _tps = round(_est_out / _elapsed, 2) if _elapsed > 0 else 0
-                                _ctx_pct = min(round((_est_in / ctx.context_length) * 100, 1), 100.0) if ctx.context_length else 0
+                                _actual_context_length = _chat_request_state["context_lengths"].get(
+                                    _actual_candidate_index,
+                                    _selected_context_length,
+                                )
+                                _actual_request_messages = _chat_request_state["requests"].get(
+                                    _actual_candidate_index,
+                                    messages,
+                                )
+                                _est_in = estimate_tokens(_actual_request_messages)
+                                _ctx_pct = min(round((_est_in / _actual_context_length) * 100, 1), 100.0) if _actual_context_length else 0
                                 last_metrics = {
                                     "response_time": round(_elapsed, 2),
                                     "input_tokens": _est_in,
@@ -1611,13 +2003,25 @@ def setup_chat_routes(
                                     "tokens_per_second": _tps,
                                     "request_context_tokens": _est_in,
                                     "context_percent": _ctx_pct,
-                                    "context_length": ctx.context_length,
+                                    "context_length": _actual_context_length,
                                     "model": _actual_model or _answered_by or _requested_model,
                                     "requested_model": _requested_model,
+                                    "requested_endpoint_id": _requested_route.get("endpoint_id"),
+                                    "requested_endpoint_label": _requested_route.get("endpoint_label"),
+                                    "endpoint_id": _actual_route.get("endpoint_id"),
+                                    "endpoint_label": _actual_route.get("endpoint_label"),
                                     "usage_source": "estimated",
                                 }
+                                if isinstance(
+                                    _actual_route.get("endpoint_cost_tracked"),
+                                    bool,
+                                ):
+                                    last_metrics["endpoint_cost_tracked"] = _actual_route.get(
+                                        "endpoint_cost_tracked"
+                                    )
                                 yield f'data: {json.dumps({"type": "metrics", "data": last_metrics})}\n\n'
                             if full_response:
+                                _commit_chat_compaction(_actual_candidate_index)
                                 _metrics_to_save = dict(last_metrics or {})
                                 if thinking_response.strip() and not _metrics_to_save.get("thinking"):
                                     _metrics_to_save["thinking"] = thinking_response.strip()
@@ -1652,6 +2056,10 @@ def setup_chat_routes(
                                 "stopped": True,
                                 "model": _actual_model or _answered_by or _requested_model,
                                 "requested_model": _requested_model,
+                                "endpoint_id": _actual_route.get("endpoint_id"),
+                                "endpoint_label": _actual_route.get("endpoint_label"),
+                                "requested_endpoint_id": _requested_route.get("endpoint_id"),
+                                "requested_endpoint_label": _requested_route.get("endpoint_label"),
                             },
                         )
                         sess.add_message(ChatMessage("assistant", _stopped_content, metadata=_stopped_md))
@@ -1666,6 +2074,12 @@ def setup_chat_routes(
                 _answered_by = None  # set if the selected model failed and a fallback answered
                 _requested_model = sess.model
                 _actual_model = None
+                _agent_requested_route = _foreground_route_descriptors[0]
+                _agent_actual_endpoint_id = _agent_requested_route.get("endpoint_id")
+                _agent_actual_endpoint_label = _agent_requested_route.get("endpoint_label")
+                _agent_round_models = {1: _requested_model}
+                _agent_round_endpoint_ids = {1: _agent_actual_endpoint_id}
+                _agent_round_endpoint_labels = {1: _agent_actual_endpoint_label}
                 try:
                     from src.settings import get_setting
                     from src.agent_tools import MAX_AGENT_ROUNDS as _DEFAULT_ROUNDS
@@ -1703,19 +2117,24 @@ def setup_chat_routes(
                         prompt_type=preset_id,
                         max_tool_calls=_tool_budget,
                         max_rounds=_max_rounds,
-                        context_length=ctx.context_length,
+                        context_length=_selected_context_length,
                         active_document=active_doc,
                         active_email=active_email_ctx,
                         session_id=session,
+                        history_session=sess,
                         disabled_tools=disabled_tools if disabled_tools else None,
                         tool_policy=tool_policy,
                         owner=_user,
                         fallbacks=_foreground_candidates[1:],
+                        route_descriptors=_foreground_route_descriptors,
+                        fallback_statuses=_foreground_policy.eligible_statuses,
+                        fallback_on_empty=_foreground_policy.fallback_on_empty,
                         plan_mode=plan_mode,
                         approved_plan=approved_plan or None,
                         workspace=workspace or None,
                         forced_tools=_forced_tools,
                         uploaded_files=ctx.uploaded_files,
+                        defer_context_shaping=_foreground_policy.enabled,
                     ):
                         if chunk.startswith("data: ") and not chunk.startswith("data: [DONE]"):
                             try:
@@ -1744,7 +2163,20 @@ def setup_chat_routes(
                                     "plan_update",
                                 ):
                                     if data.get("type") == "agent_step":
-                                        _agent_rounds = max(_agent_rounds, data.get("round", 1))
+                                        _event_round = data.get("round", 1)
+                                        _agent_rounds = max(_agent_rounds, _event_round)
+                                        _agent_round_models.setdefault(
+                                            _event_round,
+                                            _actual_model or _answered_by or _requested_model,
+                                        )
+                                        _agent_round_endpoint_ids.setdefault(
+                                            _event_round,
+                                            _agent_actual_endpoint_id,
+                                        )
+                                        _agent_round_endpoint_labels.setdefault(
+                                            _event_round,
+                                            _agent_actual_endpoint_label,
+                                        )
                                     elif data.get("type") == "tool_start":
                                         _agent_tool_calls += 1
                                     yield chunk
@@ -1754,13 +2186,70 @@ def setup_chat_routes(
                                     # model so metrics reflect it, not the masked
                                     # selected model.
                                     _answered_by = data.get("answered_by") or _answered_by
-                                    _actual_model = _actual_model or _answered_by
+                                    _actual_model = _answered_by or _actual_model
+                                    if "answered_by_endpoint_id" in data:
+                                        _agent_actual_endpoint_id = data.get("answered_by_endpoint_id")
+                                    if data.get("answered_by_endpoint_label"):
+                                        _agent_actual_endpoint_label = data.get("answered_by_endpoint_label")
+                                    _event_round = data.get("round") or max(_agent_rounds, 1)
+                                    _agent_round_models[_event_round] = _answered_by or _requested_model
+                                    _agent_round_endpoint_ids[_event_round] = _agent_actual_endpoint_id
+                                    _agent_round_endpoint_labels[_event_round] = _agent_actual_endpoint_label
                                     data["selected_model"] = data.get("selected_model") or _requested_model
                                     yield chunk
                                 elif data.get("type") == "model_actual":
                                     _actual_model = data.get("model") or _actual_model
+                                    if "endpoint_id" in data:
+                                        _agent_actual_endpoint_id = data.get("endpoint_id")
+                                    if data.get("endpoint_label"):
+                                        _agent_actual_endpoint_label = data.get("endpoint_label")
+                                    _event_round = data.get("round") or max(_agent_rounds, 1)
+                                    _agent_round_models[_event_round] = _actual_model or _requested_model
+                                    _agent_round_endpoint_ids[_event_round] = _agent_actual_endpoint_id
+                                    _agent_round_endpoint_labels[_event_round] = _agent_actual_endpoint_label
                                     data["requested_model"] = _requested_model
                                     yield f'data: {json.dumps(data)}\n\n'
+                                elif data.get("type") == "agent_terminal":
+                                    terminal_metadata = dict(data.get("data") or {})
+                                    last_metrics = terminal_metadata
+                                    failure = terminal_metadata.get("failure") or {}
+                                    failure_status = _normalize_http_status(
+                                        failure.get("status")
+                                    )
+                                    failure_message = (
+                                        f"Model request failed (HTTP {failure_status})"
+                                        if failure_status is not None
+                                        else "Model request failed"
+                                    )
+                                    terminal_metadata["failure"] = {
+                                        "status": failure_status,
+                                        "message": failure_message,
+                                    }
+                                    terminal_content = full_response.strip()
+                                    failure_note = f"[Agent stopped: {failure_message}]"
+                                    if terminal_content:
+                                        terminal_content = f"{terminal_content}\n\n{failure_note}"
+                                    else:
+                                        terminal_content = failure_note
+                                    if not _terminal_saved:
+                                        _saved_id = save_assistant_response(
+                                            sess,
+                                            session_manager,
+                                            session,
+                                            terminal_content,
+                                            terminal_metadata,
+                                            character_name=ctx.preset.character_name,
+                                            web_sources=web_sources,
+                                            rag_sources=ctx.rag_sources,
+                                            used_memories=ctx.used_memories,
+                                            incognito=incognito,
+                                        )
+                                        _terminal_saved = True
+                                        accumulate_token_usage(session, terminal_metadata)
+                                        _stream_set(session, status="error")
+                                        if _saved_id:
+                                            yield f'data: {json.dumps({"type": "message_saved", "id": _saved_id})}\n\n'
+                                    yield chunk
                                 elif data.get("type") == "metrics":
                                     last_metrics = data.get("data", {})
                                     _reported_model = last_metrics.get("model")
@@ -1772,7 +2261,16 @@ def setup_chat_routes(
                                         last_metrics["context_messages_after_trim"] = ctx.context_messages_after_trim
                                         last_metrics["context_tokens_before_trim"] = ctx.context_tokens_before_trim
                                         last_metrics["context_tokens_after_trim"] = ctx.context_tokens_after_trim
-                                    yield f'data: {json.dumps({"type": "metrics", "data": last_metrics})}\n\n'
+                                    _metrics_event = {"type": "metrics", "data": last_metrics}
+                                    # Inline teacher escalation marks its
+                                    # recursively emitted events at the SSE
+                                    # envelope. Preserve that non-secret marker
+                                    # when normalizing metrics so the browser's
+                                    # replay-stable ledger keeps primary and
+                                    # teacher segments distinct.
+                                    if data.get("teacher") is True:
+                                        _metrics_event["teacher"] = True
+                                    yield f'data: {json.dumps(_metrics_event)}\n\n'
                             except json.JSONDecodeError:
                                 yield chunk
                         elif chunk.startswith("event: "):
@@ -1824,6 +2322,22 @@ def setup_chat_routes(
                                     "stopped": True,
                                     "model": _actual_model or _answered_by or _requested_model,
                                     "requested_model": _requested_model,
+                                    "endpoint_id": _agent_actual_endpoint_id,
+                                    "endpoint_label": _agent_actual_endpoint_label,
+                                    "requested_endpoint_id": _agent_requested_route.get("endpoint_id"),
+                                    "requested_endpoint_label": _agent_requested_route.get("endpoint_label"),
+                                    "round_models": [
+                                        _agent_round_models.get(i, _actual_model or _requested_model)
+                                        for i in range(1, max(_agent_round_models, default=1) + 1)
+                                    ],
+                                    "round_endpoint_ids": [
+                                        _agent_round_endpoint_ids.get(i)
+                                        for i in range(1, max(_agent_round_models, default=1) + 1)
+                                    ],
+                                    "round_endpoint_labels": [
+                                        _agent_round_endpoint_labels.get(i)
+                                        for i in range(1, max(_agent_round_models, default=1) + 1)
+                                    ],
                                 },
                             )
                             sess.add_message(ChatMessage("assistant", _stopped_content2, metadata=_stopped_md2))
@@ -1866,8 +2380,12 @@ def setup_chat_routes(
         if compare_mode:
             return StreamingResponse(_safe_stream(), media_type="text/event-stream")
 
-        agent_runs.start(session, _safe_stream())
+        _detached_run = agent_runs.start(session, _safe_stream())
-        return StreamingResponse(agent_runs.subscribe(session), media_type="text/event-stream")
+        return StreamingResponse(
+            agent_runs.subscribe(session, _detached_run),
+            media_type="text/event-stream",
+            headers={"X-Odysseus-Run-Id": _detached_run.run_id},
+        )
 
     # ------------------------------------------------------------------ #
     # GET /api/chat/resume — reconnect to a detached run that's still going
@@ -1876,9 +2394,14 @@ def setup_chat_routes(
     @router.get("/api/chat/resume/{session_id}")
     async def chat_resume(request: Request, session_id: str) -> StreamingResponse:
         _verify_session_owner(request, session_id)
-        if not agent_runs.is_active(session_id):
+        _active_run = agent_runs.get_active_run(session_id)
+        if _active_run is None:
             raise HTTPException(404, "No active run for this session")
-        return StreamingResponse(agent_runs.subscribe(session_id), media_type="text/event-stream")
+        return StreamingResponse(
+            agent_runs.subscribe(session_id, _active_run),
+            media_type="text/event-stream",
+            headers={"X-Odysseus-Run-Id": _active_run.run_id},
+        )
 
     # ------------------------------------------------------------------ #
     # POST /api/chat/stop — cancel a detached run (Stop button). Closing the SSE
@@ -1887,7 +2410,8 @@ def setup_chat_routes(
     @router.post("/api/chat/stop/{session_id}")
     async def chat_stop(request: Request, session_id: str) -> Dict[str, Any]:
         _verify_session_owner(request, session_id)
-        stopped = agent_runs.stop(session_id)
+        _expected_run_id = request.headers.get("X-Odysseus-Run-Id")
+        stopped = agent_runs.stop(session_id, _expected_run_id)
         return {"stopped": stopped}
 
     # ------------------------------------------------------------------ #

routes/email_routes.py

@@ -5004,7 +5004,6 @@ def setup_email_routes():
             from src.endpoint_resolver import (
                 resolve_endpoint,
                 resolve_utility_fallback_candidates,
-                resolve_chat_fallback_candidates,
             )
             from src.llm_core import llm_call_async_with_fallback
 
@@ -5066,8 +5065,6 @@ def setup_email_routes():
                 pass
             for cand in resolve_utility_fallback_candidates(owner=owner) or []:
                 _add(*cand)
-            for cand in resolve_chat_fallback_candidates(owner=owner) or []:
-                _add(*cand)
             if not candidates:
                 return {"success": False, "error": "No LLM endpoint configured"}
 
@@ -5327,13 +5324,11 @@ def setup_email_routes():
             # Build a candidate chain so a stale session-stored API key
             # (the most common cause of "authentication failed" here)
             # doesn't kill AI Reply outright — fall through to the
-            # user's Utility / Default endpoints and the active Utility
+            # user's Utility / Default endpoints and active Utility fallback
-            # fallback chain. The retired default-fallback hook stays empty.
+            # chain. Dedupe by url+model so we don't retry the same endpoint.
-            # Dedupe by url+model so we don't retry the same broken endpoint.
             from src.llm_core import llm_call_async_with_fallback
             from src.endpoint_resolver import (
                 resolve_utility_fallback_candidates,
-                resolve_chat_fallback_candidates,
             )
             _seen = set()
             _candidates = []
@@ -5358,11 +5353,9 @@ def setup_email_routes():
                 _add(_d_url, _d_model, _d_headers)
             except Exception:
                 pass
-            # Active Utility fallbacks, then the retired default hook.
+            # Active Utility fallbacks last.
             for cand in resolve_utility_fallback_candidates(owner=owner) or []:
                 _add(*cand)
-            for cand in resolve_chat_fallback_candidates(owner=owner) or []:
-                _add(*cand)
             _messages = [
                 {"role": "system", "content": system_prompt},
                 {"role": "user", "content": user_msg},

routes/model_routes.py

@@ -46,6 +46,7 @@ _ENDPOINT_SETTING_FIELDS = {
 }
 
 _ENDPOINT_FALLBACK_FIELDS = {
+    "foreground_model_fallbacks": "Foreground Model Fallbacks",
     "utility_model_fallbacks": "Utility Model Fallbacks",
     "vision_model_fallbacks":  "Vision Model Fallbacks",
 }
@@ -180,7 +181,12 @@ def _clear_user_pref_endpoint_refs(all_prefs: dict, ep_id: str) -> int:
     if not isinstance(all_prefs, dict):
         return 0
     users = all_prefs.get("_users")
-    pref_sets = users.values() if isinstance(users, dict) else [all_prefs]
+    # A mixed store can contain auth-disabled foreground policy at the root
+    # alongside named-owner preferences. Both are active namespaces; legacy
+    # `default_model_fallbacks` remains untouched by the field allowlist.
+    pref_sets = [all_prefs]
+    if isinstance(users, dict):
+        pref_sets.extend(users.values())
     cleared_users = 0
     for prefs in pref_sets:
         if isinstance(prefs, dict) and _clear_endpoint_settings_for_endpoint(prefs, ep_id):

routes/prefs_routes.py

@@ -7,6 +7,10 @@ from src.auth_helpers import get_current_user
 from src.constants import USER_PREFS_FILE
 
 PREFS_FILE = USER_PREFS_FILE
+_FOREGROUND_POLICY_KEYS = (
+    "foreground_fallback_enabled",
+    "foreground_model_fallbacks",
+)
 
 
 def _load():
@@ -26,14 +30,27 @@ def _save(prefs):
 def _load_for_user(user: Optional[str] = None) -> dict:
     """Load preferences for a specific user."""
     all_prefs = _load()
-    if "_users" in all_prefs:
+    users = all_prefs.get("_users")
+    if isinstance(users, dict):
         if user is None:
             # Auth disabled — return first user's prefs for backward compat
-            users = all_prefs["_users"]
+            prefs = dict(next(iter(users.values()), {}))
-            return dict(next(iter(users.values()), {}))
+            # Foreground fallback consent is never borrowed from a named
-        return dict(all_prefs["_users"].get(user, {}))
+            # owner. Auth-disabled operation has a separate flat/root opt-in
-    # Legacy flat format — return as-is
+            # that remains inert when authentication is enabled again.
-    return dict(all_prefs)
+            for key in _FOREGROUND_POLICY_KEYS:
+                prefs.pop(key, None)
+                if key in all_prefs:
+                    prefs[key] = all_prefs[key]
+            return prefs
+        prefs = users.get(user, {})
+        return dict(prefs) if isinstance(prefs, dict) else {}
+    # A legacy flat store belongs only to auth-disabled single-user mode.
+    # Copying it into the first named user's new `_users` record during an
+    # auth transition would silently transfer another user's preferences and,
+    # critically, foreground fallback consent. Named owners therefore start
+    # with an empty record and must write their own preferences explicitly.
+    return dict(all_prefs) if user is None else {}
 
 
 def _save_for_user(user: Optional[str], prefs: dict):
@@ -45,17 +62,40 @@ def _save_for_user(user: Optional[str], prefs: dict):
         # `prefs` flat would overwrite the whole `_users` map and destroy every
         # other user's preferences. Instead write back into the same (first)
         # slot _load_for_user(None) reads from, preserving the others.
-        if "_users" in all_prefs:
+        users = all_prefs.get("_users")
-            users = all_prefs["_users"]
+        if isinstance(users, dict):
             first_key = next(iter(users), None)
             if first_key is not None:
-                users[first_key] = prefs
+                existing_named = users.get(first_key)
+                existing_named = (
+                    dict(existing_named)
+                    if isinstance(existing_named, dict)
+                    else {}
+                )
+                named_foreground = {
+                    key: existing_named[key]
+                    for key in _FOREGROUND_POLICY_KEYS
+                    if key in existing_named
+                }
+                users[first_key] = {
+                    key: value
+                    for key, value in prefs.items()
+                    if key not in _FOREGROUND_POLICY_KEYS
+                }
+                users[first_key].update(named_foreground)
+                for key in _FOREGROUND_POLICY_KEYS:
+                    if key in prefs:
+                        all_prefs[key] = prefs[key]
                 _save(all_prefs)
                 return
         _save(prefs)
         return
-    if "_users" not in all_prefs:
+    if not isinstance(all_prefs.get("_users"), dict):
-        all_prefs = {"_users": {}}
+        # Preserve the flat single-user object as inert legacy data while
+        # creating the first named-owner namespace. In particular, historical
+        # fallback values must not be deleted or copied into the new owner.
+        all_prefs = dict(all_prefs)
+        all_prefs["_users"] = {}
     all_prefs["_users"][user] = prefs
     _save(all_prefs)
 

src/agent_runs.py

@@ -17,13 +17,14 @@ close / navigation / refresh). It does NOT survive a server restart.
 import asyncio
 import json
 import logging
+import uuid
 from typing import AsyncGenerator, Dict, Optional
 
 logger = logging.getLogger(__name__)
 
 
 class _Run:
-    __slots__ = ("buffer", "subscribers", "status", "task", "evict_task")
+    __slots__ = ("buffer", "subscribers", "status", "task", "evict_task", "run_id")
 
     def __init__(self) -> None:
         self.buffer: list = []          # ordered SSE event strings (replay log)
@@ -31,6 +32,9 @@ class _Run:
         self.status: str = "running"    # running | done | error | stopped
         self.task: Optional[asyncio.Task] = None
         self.evict_task: Optional[asyncio.Task] = None
+        # Stable across every subscription/replay of this exact detached run.
+        # The browser uses it to make local cost accounting replay-idempotent.
+        self.run_id: str = uuid.uuid4().hex
 
 
 _RUNS: Dict[str, _Run] = {}
@@ -53,13 +57,24 @@ def _publish(run: _Run, ev: str) -> None:
             pass
 
 
-def _schedule_evict(session_id: str) -> None:
+def _wake_run_subscribers(run: _Run) -> None:
+    """Close subscribers even when the drain task never reached its body."""
+    for q in list(run.subscribers):
+        try:
+            q.put_nowait((None, None))
+        except Exception:
+            pass
+
+
+def _schedule_evict(session_id: str, expected_run: Optional[_Run] = None) -> None:
     """(Re)arm a grace-period eviction for a terminal run with no subscribers.
     Identity-checked so a run that gets replaced/reused is never evicted by a
     stale timer."""
     run = _RUNS.get(session_id)
     if run is None:
         return
+    if expected_run is not None and run is not expected_run:
+        return
     if run.evict_task and not run.evict_task.done():
         run.evict_task.cancel()
 
@@ -85,25 +100,38 @@ def get_status(session_id: str) -> Optional[str]:
     return r.status if r else None
 
 
-async def _drain(session_id: str, agen: AsyncGenerator[str, None],
+def get_run_id(session_id: str) -> Optional[str]:
+    """Return the opaque identity of the current detached run, if present."""
+    r = _RUNS.get(session_id)
+    return r.run_id if r else None
+
+
+def get_active_run(session_id: str) -> Optional[_Run]:
+    """Return the exact active run currently registered for a session."""
+    r = _RUNS.get(session_id)
+    return r if r and r.status == "running" else None
+
+
+async def _drain(session_id: str, run: _Run, agen: AsyncGenerator[str, None],
                  prev_task: Optional[asyncio.Task] = None) -> None:
     """Pull every event from the wrapped generator into the run buffer, fanning
     each out to live subscribers. Runs to completion regardless of subscribers."""
-    run = _RUNS.get(session_id)
+    subscribers_woken = False
-    if run is None:
+
+    def _wake_subscribers() -> None:
+        nonlocal subscribers_woken
+        if subscribers_woken:
             return
+        subscribers_woken = True
+        _wake_run_subscribers(run)
+
     # If this run replaced an in-flight one (rapid double-send), wait for that
     # one to fully finish first. Its CancelledError handler calls aclose(), which
     # persists its partial response — letting it complete before we start writing
     # keeps the two runs' session saves sequential instead of interleaved.
+    try:
         if prev_task is not None and not prev_task.done():
-        try:
             await asyncio.wait({prev_task})
-        except asyncio.CancelledError:
-            raise            # our own cancellation — propagate
-        except Exception:
-            pass
-    try:
         async for ev in agen:
             _publish(run, ev)
         if run.status == "running":
@@ -116,6 +144,16 @@ async def _drain(session_id: str, agen: AsyncGenerator[str, None],
             await agen.aclose()
         except Exception:
             pass
+        # A rapid third replacement can cancel this task while it is still
+        # waiting for its predecessor. Close this run's subscribers promptly,
+        # but keep the task alive until the predecessor finishes so the next
+        # run still observes the transitive session-save ordering barrier.
+        _wake_subscribers()
+        if prev_task is not None and not prev_task.done():
+            try:
+                await asyncio.shield(prev_task)
+            except (asyncio.CancelledError, Exception):
+                pass
     except Exception as e:
         logger.error("[agent-run] %s failed: %s", session_id, e, exc_info=True)
         run.status = "error"
@@ -127,15 +165,11 @@ async def _drain(session_id: str, agen: AsyncGenerator[str, None],
         _publish(run, "data: [DONE]\n\n")
     finally:
         # Wake every subscriber with the end sentinel so their SSE closes.
-        for q in list(run.subscribers):
+        _wake_subscribers()
-            try:
-                q.put_nowait((None, None))
-            except Exception:
-                pass
         # Run is terminal — arm the grace timer so it (and its buffer) is
         # eventually freed even if nobody ever reconnects. subscribe() cancels
         # this on connect and re-arms on disconnect.
-        _schedule_evict(session_id)
+        _schedule_evict(session_id, run)
 
 
 def start(session_id: str, agen: AsyncGenerator[str, None]) -> _Run:
@@ -145,20 +179,37 @@ def start(session_id: str, agen: AsyncGenerator[str, None]) -> _Run:
     prev_task: Optional[asyncio.Task] = None
     if prev:
         if prev.task and not prev.task.done():
+            # A task cancelled before its first instruction never enters
+            # _drain(), so its except/finally blocks cannot update status or
+            # wake a response already bound to this exact run. Terminalize it
+            # synchronously before cancelling; _drain's cleanup is idempotent
+            # when the task had already started.
+            if prev.status == "running":
+                prev.status = "stopped"
+                _wake_run_subscribers(prev)
             prev.task.cancel()
             prev_task = prev.task   # new run awaits this before it starts writing
         if prev.evict_task and not prev.evict_task.done():
             prev.evict_task.cancel()
     run = _Run()
     _RUNS[session_id] = run
-    run.task = asyncio.create_task(_drain(session_id, agen, prev_task))
+    run.task = asyncio.create_task(_drain(session_id, run, agen, prev_task))
     return run
 
 
-async def subscribe(session_id: str) -> AsyncGenerator[str, None]:
+async def subscribe(
+    session_id: str,
+    expected_run: Optional[_Run] = None,
+) -> AsyncGenerator[str, None]:
     """Replay the run's buffer from the start, then stream live until it ends.
-    Safe to call repeatedly (reconnect) and from multiple clients at once."""
+    Safe to call repeatedly (reconnect) and from multiple clients at once.
-    run = _RUNS.get(session_id)
+
+    ``expected_run`` binds a lazy StreamingResponse body to the same run whose
+    identity was put in its response headers. Without that binding, a rapid
+    replacement between response construction and body iteration could replay
+    the replacement run under the prior run's identity.
+    """
+    run = expected_run or _RUNS.get(session_id)
     if run is None:
         return
     q: asyncio.Queue = asyncio.Queue()
@@ -201,12 +252,19 @@ async def subscribe(session_id: str) -> AsyncGenerator[str, None]:
         # Last subscriber gone on a finished run — (re)arm eviction so the
         # buffer doesn't linger indefinitely.
         if not run.subscribers and run.status != "running":
-            _schedule_evict(session_id)
+            _schedule_evict(session_id, run)
 
 
-def stop(session_id: str) -> bool:
+def stop(session_id: str, expected_run_id: Optional[str] = None) -> bool:
-    """Cancel an in-flight run (the wrapped generator saves its partial)."""
+    """Cancel the matching in-flight run (which saves its partial output).
+
+    A stale browser may issue Stop after another tab has replaced the session's
+    run. Once the caller knows its opaque run identity, fail closed rather than
+    cancelling that newer run.
+    """
     run = _RUNS.get(session_id)
+    if not expected_run_id or run is None or run.run_id != expected_run_id:
+        return False
     if run and run.task and not run.task.done():
         run.task.cancel()
         return True

src/agent_tools/admin_tools.py

@@ -510,7 +510,12 @@ async def do_manage_settings(content: str, owner: Optional[str] = None) -> Dict:
         # set/get/list/delete operate on the REAL app settings (the same store
         # the Settings panel writes), so changing a model / voice / search
         # engine / reminder channel from chat actually takes effect.
-        from src.settings import load_settings, save_settings, DEFAULT_SETTINGS
+        from src.settings import (
+            DEFAULT_SETTINGS,
+            RETIRED_SETTING_KEYS,
+            load_settings,
+            save_settings,
+        )
 
         # Secrets/credentials the agent must NOT write: kept read-only (masked)
         # so API keys never flow through chat. User sets these in the panel.
@@ -562,6 +567,9 @@ async def do_manage_settings(content: str, owner: Optional[str] = None) -> Dict:
                 return k2
             return _ALIASES_SET.get(k2, (k or "").strip())
 
+        def _is_managed_key(key):
+            return key in DEFAULT_SETTINGS and key not in RETIRED_SETTING_KEYS
+
         _ENUMS = {
             "image_quality": ["low", "medium", "high"],
             "reminder_channel": ["browser", "email", "ntfy", "webhook"],
@@ -624,14 +632,18 @@ async def do_manage_settings(content: str, owner: Optional[str] = None) -> Dict:
 
         if action == "list":
             s = load_settings()
-            shown = {k: _mask(k, v) for k, v in s.items() if k in DEFAULT_SETTINGS and not isinstance(v, dict)}
+            shown = {
+                k: _mask(k, v)
+                for k, v in s.items()
+                if _is_managed_key(k) and not isinstance(v, dict)
+            }
             return {"response": f"{len(shown)} settings (use get/set with a key)", "settings": shown, "exit_code": 0}
 
         elif action == "get":
             key = _resolve(args.get("key", ""))
             if not key:
                 return {"error": "key is required", "exit_code": 1}
-            if key not in DEFAULT_SETTINGS:
+            if not _is_managed_key(key):
                 return {"error": f"Unknown setting '{args.get('key')}'. Use action='list' to see them.", "exit_code": 1}
             val = load_settings().get(key, DEFAULT_SETTINGS.get(key))
             return {"response": f"{key} = {_mask(key, val)}", "value": _mask(key, val), "exit_code": 0}
@@ -642,11 +654,11 @@ async def do_manage_settings(content: str, owner: Optional[str] = None) -> Dict:
             if not raw:
                 return {"error": "key is required", "exit_code": 1}
             key = _resolve(raw)
-            if key not in DEFAULT_SETTINGS:
+            if not _is_managed_key(key):
                 return {"error": f"Unknown setting '{raw}'. Use action='list' to see available settings.", "exit_code": 1}
             if _is_secret(key):
                 return {"response": f"'{key}' is a credential/secret. For security I can't set it from chat. Open Settings and set it there.", "exit_code": 0}
-            # Structured settings (dicts/lists like keybinds, default_model_fallbacks)
+            # Structured settings (dicts/lists like keybinds or vision fallbacks)
             # have no safe scalar coercion; _coerce would pass a bare string
             # straight through and clobber the structure. Refuse them here; they're
             # edited in their dedicated panels. (reset/delete still restore the
@@ -675,7 +687,7 @@ async def do_manage_settings(content: str, owner: Optional[str] = None) -> Dict:
 
         elif action == "delete" or action == "reset":
             key = _resolve(args.get("key", ""))
-            if key not in DEFAULT_SETTINGS:
+            if not _is_managed_key(key):
                 return {"error": f"Unknown setting '{args.get('key')}'.", "exit_code": 1}
             if _is_secret(key):
                 return {"response": f"'{key}' is a credential. Reset it in the panel.", "exit_code": 0}

src/context_compactor.py

@@ -282,7 +282,9 @@ def trim_for_context(messages: List[Dict], context_length: int, reserve_tokens:
     if essential_system:
         sys_text = essential_system[0].get("content", "")
         if len(sys_text) > 2000:
-            essential_system[0] = {"role": "system", "content": sys_text[:2000] + "\n[System prompt truncated for context limits]"}
+            truncated_system = dict(essential_system[0])
+            truncated_system["content"] = sys_text[:2000] + "\n[System prompt truncated for context limits]"
+            essential_system[0] = truncated_system
             trimmed = essential_system + convo_msgs
             if estimate_tokens(trimmed) <= budget:
                 return _sanitize_tool_messages(essential_system + protected_msgs + convo_msgs)
@@ -325,6 +327,9 @@ async def maybe_compact(
     messages: List[Dict],
     headers: Optional[Dict] = None,
     owner: Optional[str] = None,
+    *,
+    persist: bool = True,
+    compaction_state: Optional[Dict[str, Any]] = None,
 ) -> tuple:
     """Check context usage and compact if above threshold.
 
@@ -416,7 +421,17 @@ async def maybe_compact(
     # offset — session.history INCLUDES the system messages, but
     # split_point is indexed against convo_msgs which does NOT. Without
     # this, the slice drops the leading system message(s).
+    if compaction_state is not None:
+        compaction_state.update({
+            "split_point": split_point,
+            "summary": summary,
+            "system_msg_count": len(system_msgs),
+            "applied": False,
+        })
+    if persist:
         _update_session_history(session, split_point, summary, system_msg_count=len(system_msgs))
+        if compaction_state is not None:
+            compaction_state["applied"] = True
 
     new_used = estimate_tokens(compacted)
     logger.info(
@@ -427,6 +442,51 @@ async def maybe_compact(
     return compacted, context_length, True
 
 
+def apply_compaction_state(session, compaction_state: Optional[Dict[str, Any]]) -> bool:
+    """Persist a route-specific compaction after that route commits output.
+
+    Candidate prompts may be compacted speculatively while an explicit
+    foreground fallback chain is being tried.  Persisting at construction time
+    would let an unavailable route rewrite history before another route answers,
+    so callers hold this small plan and apply only the winning route's plan.
+    """
+
+    state = compaction_state if isinstance(compaction_state, dict) else None
+    if not state or state.get("applied"):
+        return False
+    summary = state.get("summary")
+    split_point = state.get("split_point")
+    system_msg_count = state.get("system_msg_count", 0)
+    if not isinstance(summary, str) or not isinstance(split_point, int):
+        return False
+    _update_session_history(
+        session,
+        split_point,
+        summary,
+        system_msg_count=system_msg_count if isinstance(system_msg_count, int) else 0,
+    )
+    state["applied"] = True
+    return True
+
+
+def apply_compaction_state_for_session(
+    session_id: Optional[str],
+    compaction_state: Optional[Dict[str, Any]],
+) -> bool:
+    """Resolve an in-memory session and apply a deferred compaction plan."""
+
+    if not session_id:
+        return False
+    try:
+        from core.models import get_session_manager_instance
+
+        manager = get_session_manager_instance()
+        session = manager.get_session(session_id) if manager else None
+    except Exception:
+        session = None
+    return apply_compaction_state(session, compaction_state) if session else False
+
+
 def _update_session_history(session, split_point: int, summary: str,
                             system_msg_count: int = 0):
     """Update the in-memory session history after compaction.

src/endpoint_resolver.py

@@ -5,6 +5,7 @@ Consolidates the 4+ copies of normalize_base / resolve_endpoint logic into one p
 """
 
 import json
+import ipaddress
 import logging
 import socket
 import subprocess
@@ -27,6 +28,43 @@ _NON_CHAT_MODEL = (
 )
 
 
+def endpoint_cost_tracked(url: str, endpoint_kind: Optional[str] = None) -> bool:
+    """Return whether token cost should be tracked for a concrete route.
+
+    This is intentionally a non-secret route classification.  It mirrors the
+    frontend's local/subscription exclusions without exposing endpoint URLs to
+    message metadata.
+    """
+
+    try:
+        parsed = urlparse(url or "")
+        host = (parsed.hostname or "").lower().rstrip(".")
+        path = (parsed.path or "").rstrip("/")
+    except Exception:
+        return False
+    if not host:
+        return False
+    if host == "chatgpt.com" and (
+        path == "/backend-api/codex" or path.startswith("/backend-api/codex/")
+    ):
+        return False
+    kind = str(endpoint_kind or "auto").strip().lower()
+    if kind == "local":
+        return False
+    if kind in {"api", "proxy"}:
+        return True
+    if host in {"localhost", "0.0.0.0", "host.docker.internal"} or host.endswith(".local"):
+        return False
+    try:
+        ip = ipaddress.ip_address(host)
+        return ip.is_global
+    except ValueError:
+        pass
+    if "." not in host:
+        return False
+    return True
+
+
 def _first_chat_model(models) -> Optional[str]:
     """First model that isn't an embedding/tts/etc.; falls back to models[0]."""
     for m in (models or []):
@@ -396,10 +434,14 @@ def resolve_endpoint(
         db.close()
 
 
-def resolve_endpoint_by_id(
+def _resolve_endpoint_by_id_with_descriptor(
-    ep_id: str, model: Optional[str] = None, owner: Optional[str] = None
+    ep_id: str,
-) -> Optional[Tuple[str, str, Dict]]:
+    model: Optional[str] = None,
-    """Resolve a specific endpoint id (+ optional model) to (chat_url, model, headers).
+    owner: Optional[str] = None,
+    *,
+    require_exact_model: bool = False,
+) -> Optional[Tuple[Tuple[str, str, Dict], dict]]:
+    """Resolve a concrete endpoint/model plus its non-secret descriptor.
 
     Returns None if the endpoint doesn't exist or is disabled. Used to turn
     a configured fallback entry ({endpoint_id, model}) into a dispatch target.
@@ -426,15 +468,34 @@ def resolve_endpoint_by_id(
         chat_url = build_chat_url(base)
         headers = build_headers(api_key, base)
         m = (model or "").strip()
-        # Drop a model the user disabled on the endpoint, then pick the first
+        enabled_models = _endpoint_enabled_models(ep)
-        # enabled chat model rather than a hidden one.
+        if require_exact_model:
+            # Explicit foreground fallback entries are concrete choices. A
+            # hidden or known-missing model must disable the entry instead of
+            # silently substituting another model from the endpoint.
+            if not m or m in _endpoint_hidden_models(ep):
+                return None
+            if enabled_models and m not in enabled_models:
+                return None
+        else:
+            # Legacy Utility/Vision chains retain their model-repair behavior.
             if m and m in _endpoint_hidden_models(ep):
                 m = ""
             if not m:
-            m = _first_chat_model(_endpoint_enabled_models(ep)) or ""
+                m = _first_chat_model(enabled_models) or ""
         if not m:
             return None
-        return chat_url, m, headers
+        return (
+            (chat_url, m, headers),
+            {
+                "endpoint_id": ep.id,
+                "endpoint_label": getattr(ep, "name", None) or ep.id,
+                "endpoint_cost_tracked": endpoint_cost_tracked(
+                    chat_url,
+                    getattr(ep, "endpoint_kind", None),
+                ),
+            },
+        )
     except Exception as e:
         logger.debug(f"Could not resolve endpoint {ep_id}: {e}")
         return None
@@ -442,11 +503,101 @@ def resolve_endpoint_by_id(
         db.close()
 
 
-def resolve_chat_fallback_candidates(owner: Optional[str] = None) -> list:
+def resolve_endpoint_by_id(
-    """Compatibility shim for the retired default-chat fallback chain."""
+    ep_id: str,
+    model: Optional[str] = None,
+    owner: Optional[str] = None,
+    *,
+    require_exact_model: bool = False,
+) -> Optional[Tuple[str, str, Dict]]:
+    """Resolve a specific endpoint id (+ optional model) to its runtime route."""
 
-    del owner
+    resolved = _resolve_endpoint_by_id_with_descriptor(
-    return []
+        ep_id,
+        model,
+        owner=owner,
+        require_exact_model=require_exact_model,
+    )
+    return resolved[0] if resolved else None
+
+
+def resolve_route_descriptor(
+    endpoint_url: str,
+    model: str,
+    headers: Optional[Dict] = None,
+    owner: Optional[str] = None,
+) -> dict:
+    """Return the visible endpoint identity for an already-resolved route.
+
+    Headers are compared only inside the process so two endpoints using the
+    same provider URL/model but different credentials remain distinguishable.
+    No credential material is returned or logged.
+    """
+
+    if not endpoint_url or not model:
+        return {
+            "endpoint_id": None,
+            "endpoint_label": "Selected route",
+            "endpoint_cost_tracked": endpoint_cost_tracked(endpoint_url),
+        }
+    db = SessionLocal()
+    try:
+        q = db.query(ModelEndpoint).filter(ModelEndpoint.is_enabled == True)
+        if owner:
+            from src.auth_helpers import owner_filter
+            q = owner_filter(q, ModelEndpoint, owner)
+        expected = (endpoint_url.rstrip("/"), model, headers or {})
+        for ep in q.all():
+            resolved = _resolve_endpoint_by_id_with_descriptor(
+                ep.id,
+                model,
+                owner=owner,
+                require_exact_model=True,
+            )
+            if not resolved:
+                continue
+            candidate, descriptor = resolved
+            actual = (candidate[0].rstrip("/"), candidate[1], candidate[2] or {})
+            if actual == expected:
+                return descriptor
+    except Exception as e:
+        logger.debug("Could not identify selected endpoint route: %s", e)
+    finally:
+        db.close()
+    return {
+        "endpoint_id": None,
+        "endpoint_label": "Selected route",
+        "endpoint_cost_tracked": endpoint_cost_tracked(endpoint_url),
+    }
+
+
+def resolve_route_descriptor_by_id(
+    endpoint_id: str,
+    endpoint_url: str,
+    model: str,
+    headers: Optional[Dict] = None,
+    owner: Optional[str] = None,
+) -> Optional[dict]:
+    """Resolve a selected route's identity without relying on row order.
+
+    The explicit endpoint id is still verified against the resolved runtime
+    route. This prevents stale or mismatched request metadata from being used
+    for attribution while disambiguating endpoints whose routes are otherwise
+    identical.
+    """
+
+    resolved = _resolve_endpoint_by_id_with_descriptor(
+        endpoint_id,
+        model,
+        owner=owner,
+        require_exact_model=True,
+    )
+    if not resolved:
+        return None
+    candidate, descriptor = resolved
+    expected = ((endpoint_url or "").rstrip("/"), model, headers or {})
+    actual = (candidate[0].rstrip("/"), candidate[1], candidate[2] or {})
+    return descriptor if actual == expected else None
 
 
 def resolve_utility_fallback_candidates(owner: Optional[str] = None) -> list:
@@ -460,17 +611,62 @@ def resolve_vision_fallback_candidates(owner: Optional[str] = None) -> list:
 
 
 def _resolve_fallback_candidates(setting_key: str, owner: Optional[str] = None) -> list:
-    out = []
     try:
         from src.settings import get_user_setting, load_settings
         settings = load_settings()
         chain = get_user_setting(setting_key, owner or "", settings.get(setting_key) or []) or []
     except Exception:
-        return out
+        return []
-    for entry in chain:
+    return resolve_fallback_entries(chain, owner=owner)
+
+
+def resolve_fallback_entries(
+    entries,
+    owner: Optional[str] = None,
+    *,
+    require_exact_model: bool = False,
+) -> list:
+    """Resolve ordered endpoint/model entries within the caller's owner scope."""
+
+    out = []
+    for entry in entries or []:
         if not isinstance(entry, dict):
             continue
-        resolved = resolve_endpoint_by_id(entry.get("endpoint_id", ""), entry.get("model", ""), owner=owner)
+        resolved = resolve_endpoint_by_id(
-        if resolved:
+            entry.get("endpoint_id", ""),
+            entry.get("model", ""),
+            owner=owner,
+            require_exact_model=require_exact_model,
+        )
+        if resolved and resolved not in out:
             out.append(resolved)
     return out
+
+
+def resolve_fallback_entries_with_descriptors(
+    entries,
+    owner: Optional[str] = None,
+    *,
+    require_exact_model: bool = False,
+) -> list:
+    """Resolve ordered entries while retaining safe endpoint provenance."""
+
+    out = []
+    seen = []
+    for entry in entries or []:
+        if not isinstance(entry, dict):
+            continue
+        resolved = _resolve_endpoint_by_id_with_descriptor(
+            entry.get("endpoint_id", ""),
+            entry.get("model", ""),
+            owner=owner,
+            require_exact_model=require_exact_model,
+        )
+        if not resolved:
+            continue
+        candidate, descriptor = resolved
+        if any(candidate == prior for prior in seen):
+            continue
+        seen.append(candidate)
+        out.append((candidate, descriptor))
+    return out

src/foreground_model_routing.py

@@ -1,22 +1,155 @@
-"""Foreground Chat and Agent model-routing policy.
+"""Explicit foreground Chat and Agent model-routing policy."""
 
-The selected session model is strict by default. Historical
+from dataclasses import dataclass
-``default_model_fallbacks`` values remain stored for compatibility, but this
+from typing import Any, Collection, Dict, FrozenSet, Optional, Tuple
-policy intentionally does not read or migrate them.
+
+from src.endpoint_resolver import (
+    endpoint_cost_tracked,
+    resolve_fallback_entries,
+    resolve_fallback_entries_with_descriptors,
+    resolve_route_descriptor,
+    resolve_route_descriptor_by_id,
+)
+
+_DEFAULT_FALLBACK_ENTRY_RESOLVER = resolve_fallback_entries
+
+
+FOREGROUND_FALLBACK_ENABLED_KEY = "foreground_fallback_enabled"
+FOREGROUND_FALLBACK_LIST_KEY = "foreground_model_fallbacks"
+FOREGROUND_AVAILABILITY_STATUSES: FrozenSet[int] = frozenset({
+    408, 425, 429, 500, 502, 503, 504, 507, 508, 529,
+})
+MAX_FOREGROUND_FALLBACKS = 10
+
+
+@dataclass(frozen=True)
+class ForegroundModelPolicy:
+    """Resolved per-user foreground fallback policy."""
+
+    enabled: bool = False
+    fallback_candidates: Tuple[tuple, ...] = ()
+    fallback_descriptors: Tuple[dict, ...] = ()
+    eligible_statuses: FrozenSet[int] = FOREGROUND_AVAILABILITY_STATUSES
+    fallback_on_empty: bool = False
+
+
+def _load_policy_preferences(owner: Optional[str]) -> dict:
+    """Load only preferences that explicitly belong to ``owner``.
+
+    The generic preferences loader intentionally treats a legacy flat store as
+    the single-user preferences object.  That compatibility must not cross an
+    authentication transition: once a named owner is present, foreground
+    fallback consent exists only in an actual ``_users[owner]`` dictionary.
     """
 
-from typing import Any, Dict, Optional
+    from routes import prefs_routes
+
+    if owner is None:
+        prefs = prefs_routes._load_for_user(None)
+        return dict(prefs) if isinstance(prefs, dict) else {}
+
+    raw = prefs_routes._load()
+    users = raw.get("_users") if isinstance(raw, dict) else None
+    if not isinstance(users, dict):
+        return {}
+    prefs = users.get(owner)
+    return dict(prefs) if isinstance(prefs, dict) else {}
+
+
+def resolve_foreground_model_policy(
+    owner: Optional[str] = None,
+    allowed_models: Optional[Collection[str]] = None,
+) -> ForegroundModelPolicy:
+    """Resolve an explicit owner-scoped policy, failing closed to strict mode.
+
+    The policy is stored in user preferences even when authentication is
+    disabled. Historical ``default_model_fallbacks`` values are deliberately
+    unrelated and are never read or migrated.
+    """
+
+    try:
+        prefs = _load_policy_preferences(owner)
+    except Exception:
+        return ForegroundModelPolicy()
+
+    if prefs.get(FOREGROUND_FALLBACK_ENABLED_KEY) is not True:
+        return ForegroundModelPolicy()
+
+    entries = prefs.get(FOREGROUND_FALLBACK_LIST_KEY)
+    if not isinstance(entries, list) or not entries:
+        return ForegroundModelPolicy()
+    if allowed_models is not None:
+        allowed = frozenset(allowed_models)
+        entries = [
+            entry for entry in entries
+            if (
+                isinstance(entry, dict)
+                and isinstance(entry.get("model"), str)
+                and entry.get("model") in allowed
+            )
+        ]
+        if not entries:
+            return ForegroundModelPolicy()
+    entries = entries[:MAX_FOREGROUND_FALLBACKS]
+
+    if resolve_fallback_entries is not _DEFAULT_FALLBACK_ENTRY_RESOLVER:
+        # Preserve the long-standing resolver seam used by downstream tests and
+        # integrations. Production uses the descriptor-aware resolver below.
+        compatibility_candidates = resolve_fallback_entries(
+            entries,
+            owner=owner,
+            require_exact_model=True,
+        )
+        # Known limitation of this test-only seam: alignment matches on model
+        # alone, so when two entries share a model and the resolver skips the
+        # first, the surviving candidate inherits the skipped entry's
+        # endpoint_id. Production uses the descriptor-aware branch below,
+        # which is unaffected.
+        resolved_routes = []
+        remaining_entries = list(entries)
+        for candidate in compatibility_candidates:
+            matching_index = next(
+                (
+                    index for index, entry in enumerate(remaining_entries)
+                    if isinstance(entry, dict)
+                    and entry.get("model") == candidate[1]
+                ),
+                None,
+            )
+            matching_entry = (
+                remaining_entries.pop(matching_index)
+                if matching_index is not None
+                else {}
+            )
+            descriptor = {
+                "endpoint_id": matching_entry.get("endpoint_id"),
+                "endpoint_label": matching_entry.get("endpoint_id") or "Fallback route",
+                "endpoint_cost_tracked": endpoint_cost_tracked(candidate[0]),
+            }
+            resolved_routes.append((candidate, descriptor))
+    else:
+        resolved_routes = resolve_fallback_entries_with_descriptors(
+            entries,
+            owner=owner,
+            require_exact_model=True,
+        )
+    candidates = [candidate for candidate, _descriptor in resolved_routes]
+    if not candidates:
+        return ForegroundModelPolicy()
+
+    return ForegroundModelPolicy(
+        enabled=True,
+        fallback_candidates=tuple(candidates),
+        fallback_descriptors=tuple(
+            dict(descriptor) for _candidate, descriptor in resolved_routes
+        ),
+    )
 
 
 def resolve_foreground_fallback_candidates(owner: Optional[str] = None) -> list:
-    """Return fallback candidates for a foreground Chat or Agent request.
+    """Return only candidates explicitly enabled by the current user."""
 
-    Foreground routing is strict, so no alternate endpoint/model is eligible.
+    return list(resolve_foreground_model_policy(owner).fallback_candidates)
-    ``owner`` is accepted to keep this policy boundary owner-aware.
-    """
-
-    del owner
-    return []
 
 
 def build_foreground_model_candidates(
@@ -24,8 +157,50 @@ def build_foreground_model_candidates(
     model: str,
     headers: Optional[Dict[str, Any]] = None,
     owner: Optional[str] = None,
+    policy: Optional[ForegroundModelPolicy] = None,
 ) -> list:
     """Build the ordered candidate list for a foreground request."""
 
+    policy = policy or resolve_foreground_model_policy(owner)
     primary = (endpoint_url, model, headers or {})
-    return [primary] + resolve_foreground_fallback_candidates(owner=owner)
+    candidates = [primary]
+    for candidate in policy.fallback_candidates:
+        if candidate not in candidates:
+            candidates.append(candidate)
+    return candidates
+
+
+def build_foreground_route_descriptors(
+    endpoint_url: str,
+    model: str,
+    headers: Optional[Dict[str, Any]] = None,
+    owner: Optional[str] = None,
+    policy: Optional[ForegroundModelPolicy] = None,
+    selected_endpoint_id: Optional[str] = None,
+) -> list:
+    """Build safe route metadata parallel to foreground candidates."""
+
+    policy = policy or resolve_foreground_model_policy(owner)
+    selected = None
+    if selected_endpoint_id:
+        selected = resolve_route_descriptor_by_id(
+            selected_endpoint_id,
+            endpoint_url,
+            model,
+            headers or {},
+            owner=owner,
+        )
+    if selected is None:
+        selected = resolve_route_descriptor(endpoint_url, model, headers or {}, owner=owner)
+    primary = (endpoint_url, model, headers or {})
+    candidates = [primary]
+    descriptors = [selected]
+    for candidate, descriptor in zip(
+        policy.fallback_candidates,
+        policy.fallback_descriptors,
+    ):
+        if candidate in candidates:
+            continue
+        candidates.append(candidate)
+        descriptors.append(dict(descriptor))
+    return descriptors

src/request_models.py

@@ -12,6 +12,7 @@ class ChatRequest(BaseModel):
     use_research: Optional[bool] = Field(default=False, description="Enable deep research")
     time_filter: Optional[str] = Field(default=None, description="Time filter for search")
     preset_id: Optional[str] = Field(default=None, description="Preset identifier")
+    selected_endpoint_id: Optional[str] = Field(default=None, description="Selected model endpoint ID")
     
     @field_validator('message')
     @classmethod

src/settings.py

@@ -14,6 +14,13 @@ from src.constants import SETTINGS_FILE, FEATURES_FILE
 
 logger = logging.getLogger(__name__)
 
+# Keys retained in the raw settings store for compatibility and rollback, but
+# deliberately unavailable through generic settings APIs or agent tools.  They
+# must stay in ``DEFAULT_SETTINGS`` so old files continue to load without data
+# loss; callers that present or mutate settings should use this set as a
+# tombstone boundary.
+RETIRED_SETTING_KEYS = frozenset({"default_model_fallbacks"})
+
 # Tiny TTL cache for settings/features. get_setting() is called on hot paths
 # (every chat, every preprocess); without this it re-parses the JSON each call.
 # Picks up edits within _CACHE_TTL seconds, which is fine for human-edited config.
@@ -197,6 +204,17 @@ DEFAULT_SETTINGS = {
     },
 }
 
+
+def without_retired_settings(settings: dict) -> dict:
+    """Return a shallow copy suitable for generic settings interfaces."""
+    if not isinstance(settings, dict):
+        return {}
+    return {
+        key: value
+        for key, value in settings.items()
+        if key not in RETIRED_SETTING_KEYS
+    }
+
 DEFAULT_FEATURES = {
     "web_search": True,
     "web_fetch": True,
@@ -269,7 +287,7 @@ _PER_USER_KEYS = {
     # Default chat endpoint / model — without per-user resolution every new
     # account inherited whatever the most-recent admin picked, which then
     # got injected into the chat composer on first open.
-    "default_endpoint_id", "default_model", "default_model_fallbacks",
+    "default_endpoint_id", "default_model",
     "utility_endpoint_id", "utility_model", "utility_model_fallbacks",
     "research_endpoint_id", "research_model",
 }

src/task_endpoint.py

@@ -1,7 +1,6 @@
 """Shared resolver for background-task AI endpoints."""
 
 from src.endpoint_resolver import (
-    resolve_chat_fallback_candidates,
     resolve_endpoint,
     resolve_utility_fallback_candidates,
 )
@@ -32,7 +31,6 @@ def resolve_task_candidates(
     2. Utility endpoint/model
     3. Default endpoint/model
     4. Utility fallback chain
-    5. Retired default-fallback compatibility hook (currently empty)
     """
     candidates = []
 
@@ -49,9 +47,6 @@ def resolve_task_candidates(
     _append(*resolve_endpoint("default", owner=owner))
     for url, model, headers in resolve_utility_fallback_candidates(owner=owner):
         _append(url, model, headers)
-    for url, model, headers in resolve_chat_fallback_candidates(owner=owner):
-        _append(url, model, headers)
-
     return candidates
 
 

static/index.html

@@ -1504,13 +1504,6 @@
                 <span class="adm-model-logo" id="set-defaultModelSelect-logo" style="display:inline-flex;align-items:center;justify-content:center;width:18px;height:18px;flex-shrink:0;opacity:0.9;color:var(--fg);"></span>
                 <select id="set-defaultModelSelect" class="settings-select"></select>
               </div>
-              <div class="settings-row" style="align-items:flex-start;" hidden>
-                <label class="settings-label" style="margin-top:6px;">Fallbacks</label>
-                <div style="flex:1;display:flex;flex-direction:column;gap:6px;">
-                  <div id="set-defaultFallbacks" class="settings-fallbacks"></div>
-                  <button type="button" class="settings-fallback-add" id="set-defaultAddFallback" title="Add a model to try if the one above fails">+ Add fallback</button>
-                </div>
-              </div>
               <div id="set-defaultChatMsg" style="font-size:11px;color:color-mix(in srgb, var(--fg) 45%, transparent);"></div>
             </div>
           </div>

static/js/chat.js

@@ -29,9 +29,16 @@ import {
   createThinkingAnalysisGate,
   stripLiveThinkingTags,
 } from './liveThinkingThrottle.js';
+import {
+  applyModelMetricsState,
+  applyModelRouteEventState,
+  inheritModelRouteState,
+} from './chatModelProvenance.js';
+import { createTerminalStreamError, isRecoverableStreamError } from './chatStreamErrors.js';
 
   const RESEARCH_TIMEOUT_MS = 360000;
   const DEFAULT_TIMEOUT_MS = 120000;
+  const RUN_ID_ABORT_GRACE_MS = 2000; // timeout waits this long for a run-id header before hard-aborting
   const RESEARCH_SVG = '<svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><circle cx="11" cy="11" r="8"/><path d="M21 21l-4.35-4.35"/></svg>';
 
   let API_BASE = '';
@@ -394,13 +401,27 @@ import {
     const tsSpan = roleEl.querySelector('.role-timestamp');
     const req = requestedModel || actualModel || '';
     const actual = actualModel || requestedModel || '';
-    let label = _modelRouteLabel(req, actual);
+    let label = _modelRouteLabel(
+      req,
+      actual,
+      opts.requestedEndpointLabel,
+      opts.actualEndpointLabel,
+      opts.requestedEndpointId,
+      opts.actualEndpointId,
+    );
     if (opts.suffix) label += ' (' + opts.suffix + ')';
     if (opts.characterName) label = opts.characterName;
     roleEl.textContent = label + ' ';
     _applyModelColor(roleEl, actual || req);
-    if (req && actual && !_sameModelName(req, actual)) {
+    const endpointChanged = Boolean(
-      roleEl.title = req + ' -> ' + actual + (opts.reason ? ': ' + opts.reason : '');
+      opts.requestedEndpointId
+      && opts.actualEndpointId
+      && opts.requestedEndpointId !== opts.actualEndpointId
+    );
+    if (req && actual && (!_sameModelName(req, actual) || endpointChanged)) {
+      roleEl.title = req + ' -> ' + actual
+        + (endpointChanged ? ' (' + opts.requestedEndpointLabel + ' -> ' + opts.actualEndpointLabel + ')' : '')
+        + (opts.reason ? ': ' + opts.reason : '');
     } else if (!opts.reason) {
       roleEl.removeAttribute('title');
     }
@@ -570,6 +591,11 @@ import {
   const _backgroundStreams = new Map(); // sessionId -> { status, accumulated, sourcesHtml, abortCtrl, query, metrics }
   const _activeStreams = new Map();     // sessionId -> { abortCtrl, holder, query, startedAt, cancelViewWork, finalizeView }
   const _resumingStreams = new Set();   // sessionId -> a resumeStream() reader is live (re-attach lock)
+  const _terminalSavedStreams = new Set(); // sessionId -> canonical terminal event seen by active reader
+  const _streamRunIds = new Map();      // sessionId -> opaque identity of the current send's detached run
+  const _streamGenerations = new Map(); // sessionId -> generation of the current (latest) send
+  const _sendStates = new Map();        // sessionId -> { generation, abortCtrl } of the current send, installed synchronously at send commit so Stop never has to borrow an older send's controller
+  const _pendingRunStops = new Map();   // 'sessionId:generation' -> abortCtrl|null; Stop queued for that send while it awaits headers. Keyed per send so concurrent sends' cancellation intents never displace each other.
   let _streamSessionId = null; // Session ID for the currently active reader loop
   let _lastReaderActivity = 0; // Timestamp of last reader.read() success — used to detect frozen streams
   let _webLockRelease = null;  // Function to release the Web Lock held during streaming
@@ -608,6 +634,60 @@ import {
     return now;
   }
 
+  /** Stable cost identity for one logical metrics segment within a run. */
+  function _metricsCostRecordId(runId, event) {
+    if (!runId) return '';
+    return `${runId}:${event && event.teacher ? 'teacher' : 'primary'}`;
+  }
+
+  /** POST the exact Stop for one observed run identity. */
+  function _postExactStop(sessionId, runId) {
+    fetch(`/api/chat/stop/${encodeURIComponent(sessionId)}`, {
+      method: 'POST',
+      credentials: 'same-origin',
+      headers: { 'X-Odysseus-Run-Id': runId },
+    }).catch(() => {});
+  }
+
+  /** Stop only the exact detached run whose identity this browser observed. */
+  function _stopExactRun(sessionId, abortCtrl = null) {
+    if (!sessionId) return false;
+    const runId = _streamRunIds.get(sessionId);
+    if (!runId) {
+      // Queue against the CURRENT send's generation: its POST is the only
+      // identity channel that can name the run, so the Stop fires from that
+      // send's own header arrival even if a replacement starts meanwhile.
+      const generation = _streamGenerations.get(sessionId) || 0;
+      const pendingKey = sessionId + ':' + generation;
+      if (abortCtrl || !_pendingRunStops.has(pendingKey)) {
+        _pendingRunStops.set(pendingKey, abortCtrl);
+      }
+      return false;
+    }
+    _postExactStop(sessionId, runId);
+    return true;
+  }
+
+  function _rememberStreamRunId(sessionId, runId, generation) {
+    if (!sessionId || !runId) return;
+    // A superseded send must not record its run id as the session's current
+    // identity, but it must still flush its own queued Stop: this is the only
+    // channel that can cancel that run when the replacement dies before its
+    // own POST reaches the server.
+    if (_streamGenerations.get(sessionId) === generation) {
+      _streamRunIds.set(sessionId, runId);
+    }
+    const pendingKey = sessionId + ':' + generation;
+    if (!_pendingRunStops.has(pendingKey)) return;
+    const pendingAbort = _pendingRunStops.get(pendingKey);
+    _pendingRunStops.delete(pendingKey);
+    _postExactStop(sessionId, runId);
+    if (pendingAbort && !pendingAbort.signal.aborted) {
+      pendingAbort._reason = 'user-stop';
+      pendingAbort.abort();
+    }
+  }
+
   // Sources box builder and toggleSources are now in chatRenderer.js
   var _buildSourcesBox = chatRenderer.buildSourcesBox;
 
@@ -1342,6 +1422,26 @@ import {
     if (messageInput) messageInput.disabled = false;
     updateSubmitButton('streaming', submitBtn);
     if (submitBtn) submitBtn.classList.remove('send-pending');
+    // Per-send generation, reserved SYNCHRONOUSLY before the send gate clears
+    // and before the first await: from this instant the superseded send may
+    // not clean session state, register, or POST (each checked at its own
+    // await boundaries). Session-keyed state (run id, queued Stop, cleanup
+    // rights) belongs to the latest generation only. A queued Stop from the
+    // superseded send is deliberately left in place, tagged with ITS
+    // generation: that send's still-alive POST is the only identity channel
+    // able to name its run, so the Stop fires from its own header arrival
+    // (see _rememberStreamRunId) even if this replacement dies before fetch.
+    const streamSessionId = sessionModule.getCurrentSessionId();
+    const streamGeneration = (_streamGenerations.get(streamSessionId) || 0) + 1;
+    _streamGenerations.set(streamSessionId, streamGeneration);
+    const _sendState = { generation: streamGeneration, abortCtrl: null };
+    _sendStates.set(streamSessionId, _sendState);
+    // The previous send's run identity dies with its ownership: a Stop after
+    // this instant must queue for THIS send, not fire against the old run.
+    // (The old send's own queued Stop still works — its flush carries the run
+    // id from its header, and its stale generation cannot repopulate this map.)
+    _streamRunIds.delete(streamSessionId);
+    _streamSessionId = streamSessionId;
     _sendInFlight = false;
 
     try {
@@ -1350,10 +1450,12 @@ import {
         await pendingSwitch;
       }
     } catch (_) {}
+    // Superseded while awaiting the model switch: the replacement owns the
+    // session now, and everything below (state resets, registration, POST)
+    // is its business alone.
+    if (_streamGenerations.get(streamSessionId) !== streamGeneration) return;
 
-    // Capture session ID for background stream detection
+    _terminalSavedStreams.delete(streamSessionId);
-    const streamSessionId = sessionModule.getCurrentSessionId();
-    _streamSessionId = streamSessionId;
     const streamQuery = msg;
     _touchStreamActivity(streamSessionId);
 
@@ -1373,6 +1475,7 @@ import {
     let _thinkOpen = false;
     let holder = null;
     let finalMeta = null;
+    let _canonicalTerminalSaved = false;
     let spinner = null;
     let timedOut = false;
     let processingProbeTimer = null;
@@ -1742,8 +1845,26 @@ import {
       }
 
 
+      // Superseded during preflight (uploads, document saves): a newer send
+      // owns the session. Bailing here — before registration and before the
+      // POST — keeps this stale send from overwriting the replacement's
+      // stream entry or reaching the server last, where agent_runs.start
+      // would cancel the newer run in favor of this old one.
+      if (_streamGenerations.get(streamSessionId) !== streamGeneration) {
+        // The optimistic user bubble is already in the DOM looking sent, but
+        // this message never reaches the server. Say so instead of leaving a
+        // ghost that vanishes on refresh.
+        if (_userMsgEl && _userMsgEl.parentNode) {
+          const _notSentNote = document.createElement('div');
+          _notSentNote.style.cssText = 'color: var(--color-error); font-style: italic; font-size: 0.85em; padding: 2px 0;';
+          _notSentNote.textContent = '[Not sent — superseded by a newer message]';
+          _userMsgEl.appendChild(_notSentNote);
+        }
+        return;
+      }
       abortCtrl = new AbortController();
       abortCtrl._reason = '';
+      _sendState.abortCtrl = abortCtrl;
       currentAbort = abortCtrl;
 
 	      const _tState = Storage.loadToggleState();
@@ -1755,15 +1876,28 @@ import {
         if (!abortCtrl.signal.aborted) {
           timedOut = true;
           abortCtrl._reason = 'timeout';
-          try {
+          if (_streamGenerations.get(streamSessionId) !== streamGeneration) {
-            if (streamSessionId) {
+            // Superseded send: the session's run id and Stop queue belong to
-              fetch(`/api/chat/stop/${encodeURIComponent(streamSessionId)}`, {
+            // the replacement now. Just kill this hung POST.
-                method: 'POST',
-                credentials: 'same-origin',
-              }).catch(() => {});
-            }
-          } catch (_) {}
             abortCtrl.abort();
+            return;
+          }
+          let abortNow = true;
+          try {
+            abortNow = _streamRunIds.has(streamSessionId)
+              ? _stopExactRun(streamSessionId)
+              : _stopExactRun(streamSessionId, abortCtrl);
+          } catch (_) {}
+          if (abortNow) {
+            abortCtrl.abort();
+          } else {
+            // The Stop is queued on the run-id header, but a request this
+            // stalled may never send one. Hard-abort after a short grace so
+            // the timeout still guarantees cancellation.
+            setTimeout(() => {
+              if (!abortCtrl.signal.aborted) abortCtrl.abort();
+            }, RUN_ID_ABORT_GRACE_MS);
+          }
         }
       }, timeoutMs);
       clearResponseTimeout = () => {
@@ -1912,6 +2046,8 @@ import {
         enableResearchBtn();
         return;
       }
+      const streamRunId = res.headers.get('X-Odysseus-Run-Id') || '';
+      if (streamRunId) _rememberStreamRunId(streamSessionId, streamRunId, streamGeneration);
 
       // Mark the chat log busy while streaming so screen readers wait for the
       // settled response instead of announcing every token. Cleared in finally.
@@ -1986,9 +2122,17 @@ import {
         const newRole = document.createElement('div');
         newRole.className = 'role';
         const metaS = sessionModule.getSessions().find(s => s.id === streamSessionId);
-        const requested = holder?._requestedModel || metaS?.model || modelName;
+        inheritModelRouteState(holder, roundHolder, newWrap, metaS?.model || modelName);
-        const actual = holder?._actualModel || requested;
+        const requested = newWrap._requestedModel;
-        newRole.textContent = _modelRouteLabel(requested, actual) || '';
+        const actual = newWrap._actualModel;
+        newRole.textContent = _modelRouteLabel(
+          requested,
+          actual,
+          newWrap._requestedEndpointLabel,
+          newWrap._actualEndpointLabel,
+          newWrap._requestedEndpointId,
+          newWrap._actualEndpointId,
+        ) || '';
         _applyModelColor(newRole, actual);
         newWrap.appendChild(newRole);
         const newBody = document.createElement('div');
@@ -2514,6 +2658,7 @@ import {
 
       let _nextIsError = false;
       let _streamSawDone = false;
+      let _streamTerminalError = null;
       let _firstVisibleOutputSeen = false;
       const markFirstVisibleOutput = () => {
         if (_firstVisibleOutputSeen) return;
@@ -2638,10 +2783,9 @@ import {
               // Handle SSE error events (e.g. HTTP 404 from provider)
               if (_nextIsError || json.status >= 400) {
                 _nextIsError = false;
-                const errMsg = json.text || json.error?.message || `Error ${json.status || 'unknown'}`;
+                _streamTerminalError = createTerminalStreamError(json);
-                console.error('Stream error:', errMsg);
+                console.error('Stream error:', _streamTerminalError.message);
                 if (spinner && spinner.element) spinner.destroy();
-                typewriterInto(roundHolder.querySelector('.body'), errMsg);
                 break;
               }
               if (json.delta || json.type === 'agent_prep' || json.type === 'generated_image' || json.type === 'tool_start' || json.type === 'tool_output' || json.type === 'tool_progress' || json.type === 'agent_step' || json.type === 'loop_breaker_triggered' || json.type === 'intent_nudge_exhausted' || json.type === 'doc_stream_open' || json.type === 'doc_stream_delta' || json.type === 'research_progress') {
@@ -3040,18 +3184,6 @@ import {
                   6000
                 );
                 continue;
-              } else if (json.type === 'model_fallback') {
-                // Model went offline — switched to fallback
-                var _fbData = json.data || {};
-                uiModule.showToast(
-                  `Model ${_fbData.old_model || '?'} offline — switched to ${_fbData.new_model || '?'}`,
-                  5000
-                );
-                // Update the model picker to reflect the new model
-                if (sessionModule && sessionModule.updateModelPicker) {
-                  sessionModule.updateModelPicker();
-                }
-                continue;
               } else if (json.type === 'model_info') {
                 // Update role label with model name as soon as we know it
                 if (!_isBg && holder) {
@@ -3059,6 +3191,10 @@ import {
                   if (roleEl) {
                     holder._requestedModel = json.requested_model || json.model || holder._requestedModel;
                     holder._actualModel = json.model || holder._actualModel || holder._requestedModel;
+                    holder._requestedEndpointId = json.requested_endpoint_id || json.endpoint_id || holder._requestedEndpointId || null;
+                    holder._requestedEndpointLabel = json.requested_endpoint_label || json.endpoint_label || holder._requestedEndpointLabel || 'Selected route';
+                    holder._actualEndpointId = json.endpoint_id || holder._actualEndpointId || holder._requestedEndpointId;
+                    holder._actualEndpointLabel = json.endpoint_label || holder._actualEndpointLabel || holder._requestedEndpointLabel;
                     if (json.suffix) holder._roleSuffix = json.suffix;
                     // Prepend character name if sent by server or set locally
                     var _charName = json.character_name || (presetsModule.getCharacterName ? presetsModule.getCharacterName() : '');
@@ -3066,6 +3202,10 @@ import {
                     _setRoleModelLabel(roleEl, holder._requestedModel, holder._actualModel, {
                       suffix: holder._roleSuffix,
                       characterName: holder._characterName,
+                      requestedEndpointId: holder._requestedEndpointId,
+                      requestedEndpointLabel: holder._requestedEndpointLabel,
+                      actualEndpointId: holder._actualEndpointId,
+                      actualEndpointLabel: holder._actualEndpointLabel,
                     });
                   }
                 }
@@ -3076,9 +3216,10 @@ import {
                 if (!_isBg) {
                   var _selM = _shortModel(json.selected_model || '');
                   var _ansM = _shortModel(json.answered_by || '');
-                  uiModule.showToast('⚠ ' + _selM + ' failed — answered by ' + _ansM, 6000);
+                  uiModule.showToast('Fallback: ' + _selM + ' failed — answered by ' + _ansM, 6000);
-                  if (holder) {
+                  var _fallbackHolder = applyModelRouteEventState(json, holder, roundHolder, modelName);
-                    var _rEl = holder.querySelector('.role');
+                  if (_fallbackHolder) {
+                    var _rEl = _fallbackHolder.querySelector('.role');
                     if (_rEl) {
                       var _tsS = _rEl.querySelector('.role-timestamp');
                       _rEl.textContent = _ansM + ' (fallback) ';
@@ -3086,13 +3227,14 @@ import {
                         (json.reason ? ': ' + json.reason : '') + ' — answered by ' + (json.answered_by || '');
                       _applyModelColor(_rEl, json.answered_by);
                       if (_tsS) _rEl.appendChild(_tsS);
-                      holder._requestedModel = json.selected_model || holder._requestedModel || modelName;
+                      _setRoleModelLabel(_rEl, _fallbackHolder._requestedModel, _fallbackHolder._actualModel, {
-                      const _hasResolvedActual = holder._actualModel && !_sameModelName(holder._actualModel, holder._requestedModel);
+                        suffix: _fallbackHolder._roleSuffix,
-                      holder._actualModel = _hasResolvedActual ? holder._actualModel : (json.answered_by || holder._actualModel || holder._requestedModel);
+                        characterName: _fallbackHolder._characterName,
-                      _setRoleModelLabel(_rEl, holder._requestedModel, holder._actualModel, {
-                        suffix: holder._roleSuffix,
-                        characterName: holder._characterName,
                         reason: json.reason,
+                        requestedEndpointId: _fallbackHolder._requestedEndpointId,
+                        requestedEndpointLabel: _fallbackHolder._requestedEndpointLabel,
+                        actualEndpointId: _fallbackHolder._actualEndpointId,
+                        actualEndpointLabel: _fallbackHolder._actualEndpointLabel,
                       });
                     }
                   }
@@ -3136,12 +3278,15 @@ import {
                   try { note.scrollIntoView({ block: 'end', behavior: 'smooth' }); } catch (_) { uiModule.scrollHistory && uiModule.scrollHistory(); }
                 }
               } else if (json.type === 'model_actual') {
-                if (!_isBg && holder) {
+                if (!_isBg) {
-                  holder._requestedModel = json.requested_model || holder._requestedModel || modelName;
+                  var _modelHolder = applyModelRouteEventState(json, holder, roundHolder, modelName);
-                  holder._actualModel = json.model || holder._actualModel || holder._requestedModel;
+                  if (_modelHolder) _setRoleModelLabel(_modelHolder.querySelector('.role'), _modelHolder._requestedModel, _modelHolder._actualModel, {
-                  _setRoleModelLabel(holder.querySelector('.role'), holder._requestedModel, holder._actualModel, {
+                    suffix: _modelHolder._roleSuffix,
-                    suffix: holder._roleSuffix,
+                    characterName: _modelHolder._characterName,
-                    characterName: holder._characterName,
+                    requestedEndpointId: _modelHolder._requestedEndpointId,
+                    requestedEndpointLabel: _modelHolder._requestedEndpointLabel,
+                    actualEndpointId: _modelHolder._actualEndpointId,
+                    actualEndpointLabel: _modelHolder._actualEndpointLabel,
                   });
                 }
               } else if (json.type === 'attachments') {
@@ -3227,15 +3372,60 @@ import {
                   const detail = before && after && before > after ? ` (${after}/${before} messages sent)` : '';
                   uiModule.showToast(`Context trimmed for this model${detail}`);
                 }
+              } else if (json.type === 'agent_terminal' || json.type === 'chat_terminal') {
+                // The backend persisted canonical partial output, sanitized
+                // failure metadata, and actual-route provenance before this
+                // event. The terminal catch below reloads that exact record.
+                _canonicalTerminalSaved = true;
+                _terminalSavedStreams.add(streamSessionId);
+                const priorMetrics = metrics;
+                metrics = json.data || metrics;
+                if (metrics && streamRunId) {
+                  metrics._costRecordId = _metricsCostRecordId(streamRunId, json);
+                }
+                // Direct Chat may have emitted provider usage before its
+                // terminal event. Carry that already-recorded state onto the
+                // canonical terminal metadata instead of billing it twice.
+                if (priorMetrics && priorMetrics._costRecorded && metrics) {
+                  metrics._costRecorded = true;
+                }
+                if (_isBg) {
+                  var bgTerminal = _backgroundStreams.get(streamSessionId);
+                  if (bgTerminal) {
+                    if (
+                      bgTerminal.metrics
+                      && bgTerminal.metrics._costRecorded
+                      && metrics
+                    ) {
+                      metrics._costRecorded = true;
+                    }
+                    bgTerminal.metrics = metrics;
+                    bgTerminal.status = 'completed';
+                    if (metrics) {
+                      chatRenderer.recordSessionMetricsCost(metrics, streamSessionId);
+                    }
+                  }
+                  continue;
+                }
+                if (holder && metrics) {
+                  applyModelMetricsState(metrics, holder, roundHolder, modelName);
+                  const terminalMetricsTarget = _metricsTargetForTurn();
+                  if (terminalMetricsTarget) displayMetrics(terminalMetricsTarget, metrics);
+                }
               } else if (json.type === 'metrics') {
                 metrics = json.data;
+                if (metrics && streamRunId) {
+                  metrics._costRecordId = _metricsCostRecordId(streamRunId, json);
+                }
                 if (!_isBg && holder && metrics) {
-                  holder._requestedModel = metrics.requested_model || holder._requestedModel || modelName;
+                  applyModelMetricsState(metrics, holder, roundHolder, modelName);
-                  holder._actualModel = metrics.model || holder._actualModel || holder._requestedModel;
                 }
                 if (_isBg) {
                   var bgM = _backgroundStreams.get(streamSessionId);
-                  if (bgM) bgM.metrics = json.data;
+                  if (bgM) {
+                    bgM.metrics = json.data;
+                    chatRenderer.recordSessionMetricsCost(bgM.metrics, streamSessionId);
+                  }
                   continue;
                 }
                 if (metrics) {
@@ -3616,9 +3806,17 @@ import {
                 const newRole = document.createElement('div');
                 newRole.className = 'role';
                 const metaS = sessionModule.getSessions().find(s => s.id === streamSessionId);
-                const _roundRequested = holder?._requestedModel || metaS?.model;
+                inheritModelRouteState(holder, roundHolder, newWrap, metaS?.model || modelName);
-                const _roundActual = holder?._actualModel || _roundRequested;
+                const _roundRequested = newWrap._requestedModel;
-                newRole.textContent = _modelRouteLabel(_roundRequested, _roundActual) || '';
+                const _roundActual = newWrap._actualModel;
+                newRole.textContent = _modelRouteLabel(
+                  _roundRequested,
+                  _roundActual,
+                  newWrap._requestedEndpointLabel,
+                  newWrap._actualEndpointLabel,
+                  newWrap._requestedEndpointId,
+                  newWrap._actualEndpointId,
+                ) || '';
                 _applyModelColor(newRole, _roundActual);
                 newWrap.appendChild(newRole);
                 const newBody = document.createElement('div');
@@ -3725,9 +3923,22 @@ import {
         }
       }
 
+      if (_streamTerminalError) {
+        throw _streamTerminalError;
+      }
       if (!_streamSawDone) {
+        if (!_canonicalTerminalSaved) {
           throw new Error('Stream closed before completion');
         }
+        // The backend persisted a canonical terminal record (partial output +
+        // failure metadata) before the connection died. Route through the
+        // terminal-error path so that record is reloaded; falling through to
+        // the success renderer would present the partial output as a clean
+        // completion.
+        throw createTerminalStreamError({
+          text: 'Stream closed after canonical terminal event',
+        });
+      }
 
       // The final foreground render below is authoritative. Cancel any delayed
       // live-view work instead of parsing and rendering the full round once
@@ -3746,15 +3957,25 @@ import {
       const _isBgFinal = (sessionModule.getCurrentSessionId() !== streamSessionId) || _backgroundStreams.has(streamSessionId);
       if (!_isBgFinal) {
         finalMeta = sessionModule.getSessions().find(s => s.id === sessionModule.getCurrentSessionId());
-        const _finalActualModel = metrics?.model || holder._actualModel || finalMeta?.model;
+        const _finalModelHolder = applyModelMetricsState(
-        const _finalRequestedModel = metrics?.requested_model || holder._requestedModel || finalMeta?.model || _finalActualModel;
+          metrics,
+          holder,
+          roundHolder,
+          finalMeta?.model || modelName,
+        ) || holder;
+        const _finalActualModel = _finalModelHolder._actualModel || finalMeta?.model;
+        const _finalRequestedModel = _finalModelHolder._requestedModel || finalMeta?.model || _finalActualModel;
         // Prepend character name if set
         var _charNameFinal = presetsModule.getCharacterName ? presetsModule.getCharacterName() : '';
-        const roleEl = holder.querySelector('.role');
+        const roleEl = _finalModelHolder.querySelector('.role');
         if (roleEl) {
           _setRoleModelLabel(roleEl, _finalRequestedModel, _finalActualModel, {
-            suffix: holder._roleSuffix,
+            suffix: _finalModelHolder._roleSuffix,
-            characterName: _charNameFinal || holder._characterName,
+            characterName: _charNameFinal || _finalModelHolder._characterName,
+            requestedEndpointId: _finalModelHolder._requestedEndpointId,
+            requestedEndpointLabel: _finalModelHolder._requestedEndpointLabel,
+            actualEndpointId: _finalModelHolder._actualEndpointId,
+            actualEndpointLabel: _finalModelHolder._actualEndpointLabel,
           });
         }
         holder.dataset.raw = accumulated;
@@ -4013,6 +4234,21 @@ import {
       } // end if (!_isBgFinal)
 
     } catch (err) {
+      // If a Stop or timeout was waiting for an identity header and the POST
+      // failed before producing one, keep this on the cancellation path. There
+      // is no safe headerless server cancel to send, but it must not be turned
+      // into an automatic recovery attempt either. Only this send's own
+      // queued Stop counts; a replacement's queued Stop is not ours to spend.
+      const _pendingCatchKey = streamSessionId + ':' + streamGeneration;
+      if (
+        _pendingRunStops.has(_pendingCatchKey)
+        && abortCtrl
+        && !abortCtrl.signal.aborted
+      ) {
+        _pendingRunStops.delete(_pendingCatchKey);
+        abortCtrl._reason = 'user-stop';
+        abortCtrl.abort();
+      }
       // Check if this stream was running in background — needed before any
       // stop-state write, so an errored background stream can't clobber the
       // foreground session's text.
@@ -4021,6 +4257,18 @@ import {
       _closeOpenThinkingMarkup(_isBgCatch);
       if (_isBgCatch) {
         _cancelLiveThinkingWork();
+
+        // A canonical terminal event may have been persisted immediately
+        // before the stream moved into the background. Preserve that terminal
+        // state instead of allowing the catch path to turn it back into a
+        // running/error stream.
+        const bgTerminal = _backgroundStreams.get(streamSessionId);
+        if (bgTerminal && _terminalSavedStreams.has(streamSessionId)) {
+          bgTerminal.status = 'completed';
+          if (sessionModule && sessionModule.clearStreaming) {
+            sessionModule.clearStreaming(streamSessionId);
+          }
+        }
       } else if (accumulated) {
         _catchTerminalView = _finalizeInterruptedView();
       } else {
@@ -4039,7 +4287,10 @@ import {
         // Error happened while backgrounded — update map, don't touch DOM
         console.error('Background stream error:', err);
         var bgErr = _backgroundStreams.get(streamSessionId);
-        if (bgErr && bgErr.status === 'completed') {
+        if (bgErr && (
+          bgErr.status === 'completed' || _terminalSavedStreams.has(streamSessionId)
+        )) {
+          bgErr.status = 'completed';
           // [DONE] was already processed — this error is benign (e.g. reader.read() after close)
           // Don't override the completed status; just ensure the completed dot stays
           if (sessionModule && sessionModule.clearStreaming) {
@@ -4191,8 +4442,36 @@ import {
           // cap. Only auto-recover from connection-class failures; deterministic
           // errors (unsupported tools, 4xx/5xx, parse failures) surface right away
           // instead of burning the nudge budget on a guaranteed-to-fail retry.
-          if (!(_isRecoverableStreamErr(err) && _tryAutoRecover(_catchViewHolder, accumulated, streamSessionId))) {
+          if (!(isRecoverableStreamError(err) && _tryAutoRecover(_catchViewHolder, accumulated, streamSessionId))) {
-            const errorHolder = _catchViewHolder?.querySelector('.body') || document.querySelector('.msg-ai:last-of-type .body');
+            if (err.terminalStreamError) {
+              if (_canonicalTerminalSaved || accumulated.trim()) {
+                // Let this stream's finally block clear foreground state before
+                // reselecting; otherwise selectSession would detach the already
+                // terminal reader and leave a stale background-stream marker.
+                setTimeout(async () => {
+                  if (sessionModule.getCurrentSessionId() === streamSessionId) {
+                    await sessionModule.selectSession(streamSessionId, { showLoading: false });
+                  } else {
+                    await sessionModule.loadSessions();
+                  }
+                }, 0);
+              } else {
+                const terminalBody =
+                  _catchViewHolder?.querySelector('.body')
+                  || roundHolder?.querySelector('.body')
+                  || document.querySelector('.msg-ai:last-of-type .body');
+                if (terminalBody) {
+                  const terminalNote = document.createElement('div');
+                  terminalNote.style.cssText = 'color: var(--color-error); font-style: italic; padding: 4px 0;';
+                  terminalNote.textContent = `[Error: ${err.message}]`;
+                  terminalBody.appendChild(terminalNote);
+                }
+              }
+              return;
+            }
+            const errorHolder =
+              _catchViewHolder?.querySelector('.body')
+              || document.querySelector('.msg-ai:last-of-type .body');
             if (errorHolder) {
               let errMsg = `Error: ${err.message}`;
               // Add hint for tool-call errors
@@ -4209,23 +4488,52 @@ import {
       clearResponseTimeout();
       clearProcessingProbe();
       clearFirstTokenWaitTimers();
+      // A replacement send bumps the session's generation the moment it
+      // starts, before it registers or reaches the server, so cleanup rights
+      // are decided by generation: a superseded send may remove only what it
+      // itself owns (its stream registration by controller identity, its own
+      // generation's queued Stop) and must leave session-level state — the
+      // reader session id, research marker, UI — to the replacement.
+      const _ownsStreamState =
+        _streamGenerations.get(streamSessionId) === streamGeneration;
+      const _finallyRegistered = _activeStreams.get(streamSessionId);
+      if (!_finallyRegistered || _finallyRegistered.abortCtrl === abortCtrl) {
         _activeStreams.delete(streamSessionId);
+      }
+      _pendingRunStops.delete(streamSessionId + ':' + streamGeneration);
+      if (_ownsStreamState) {
         if (_streamSessionId === streamSessionId) _streamSessionId = null;
+        if (_sendStates.get(streamSessionId) === _sendState) {
+          _sendStates.delete(streamSessionId);
+        }
+        // Superseded sends must not resync: with the replacement not yet
+        // registered, a stale sync would set isStreaming false and drop
+        // currentAbort while _sendInFlight is already false, reopening the
+        // send gate mid-preflight. The replacement syncs when it registers
+        // or finishes.
         _syncForegroundStreamGlobals();
+      }
       // Streaming done — let screen readers announce the settled response.
+      if (_ownsStreamState) {
         const _chatLogDone = document.getElementById('chat-history');
         if (_chatLogDone) _chatLogDone.setAttribute('aria-busy', 'false');
-      // Always clean up research tracking regardless of background state
+      }
-      _researchingStreamIds.delete(streamSessionId);
+      // Research markers gate /api/research/cancel in the Stop handler, so a
+      // superseded send must not strip a replacement research run's marker.
+      if (_ownsStreamState) _researchingStreamIds.delete(streamSessionId);
       if (_researchingStreamIds.size === 0) {
         var _rToggleCleanup = document.getElementById('research-toggle-btn');
         if (_rToggleCleanup) _rToggleCleanup.classList.remove('research-running');
       }
 
-      // Only reset UI state if still on the stream's session and was never backgrounded
+      // Only reset UI state if still on the stream's session, never
+      // backgrounded, and no replacement stream owns the session now — the
+      // replacement disabled the composer for its own send, so re-enabling
+      // it here would hand input back mid-stream.
       const _isBgFinally = (sessionModule.getCurrentSessionId() !== streamSessionId) || _backgroundStreams.has(streamSessionId);
+      if (_ownsStreamState) _terminalSavedStreams.delete(streamSessionId);
 
-      if (!_isBgFinally) {
+      if (!_isBgFinally && _ownsStreamState) {
         // Reset button to idle state
         updateSubmitButton('idle', submitBtn);
 
@@ -4320,69 +4628,64 @@ import {
   // the server run — otherwise closing the tab would kill the background task,
   // defeating the whole point. Only the Stop button cancels the server run.
   export function abortCurrentRequest(stopServer = false) {
-    const active = _getForegroundStreamState();
-    const abortCtrl = active ? active.abortCtrl : currentAbort;
-    if (abortCtrl) {
-      abortCtrl.abort();
-      // Don't set to null here - let catch block handle it
-    }
-    if (stopServer) {
-      try {
     const _sid = (sessionModule && sessionModule.getCurrentSessionId && sessionModule.getCurrentSessionId())
       || _streamSessionId
       || (window.sessionModule && window.sessionModule.getCurrentSessionId && window.sessionModule.getCurrentSessionId());
+    // The CURRENT send's controller comes from its send state, installed at
+    // send commit — never borrowed from the stream registry, which during the
+    // replacement's preflight still holds the superseded send's entry.
+    // Aborting that older controller here would sever the only identity
+    // channel able to name the old run. A send committed but pre-POST has a
+    // null controller: the Stop queues and there is nothing to abort yet.
+    const _sendStateNow = _sid ? _sendStates.get(_sid) : null;
+    const active = _getForegroundStreamState();
+    const abortCtrl = _sendStateNow
+      ? _sendStateNow.abortCtrl
+      : (active ? active.abortCtrl : currentAbort);
+    let abortNow = true;
+    if (stopServer) {
+      try {
         if (_sid) {
-          fetch(`/api/chat/stop/${encodeURIComponent(_sid)}`, { method: 'POST', credentials: 'same-origin' }).catch(() => {});
+          // Before response headers arrive there is no safe server-side stop
+          // identity yet. Keep the POST alive just long enough to receive that
+          // opaque id, then _rememberStreamRunId sends the exact Stop and aborts
+          // this reader. Never fall back to a headerless session-wide cancel.
+          abortNow = _stopExactRun(_sid, abortCtrl);
         }
       } catch (_) {}
     }
+    if (abortCtrl && abortNow) {
+      abortCtrl.abort();
+      // Don't set to null here - let catch block handle it
+    }
   }
 
   // ── Stall watchdog ──────────────────────────────────────────────
-  // Auto-recover a turn whose stream died (connection drop) or went silent:
+  // Auto-recover a turn whose browser stream died by reconnecting to the exact
-  // preserve the partial, then re-submit a completion handshake by reusing the
+  // detached server run. Returns false at the cap so the caller can surface
-  // existing continue/resume path. Returns false at the cap so the caller can
+  // the failure instead of retrying forever.
-  // surface the failure instead of nudging forever.
   // Only auto-recover from connection-class failures (the genuine "silently
   // died" case). Deterministic errors — unsupported tools, HTTP 4xx/5xx, JSON
   // parse failures — will fail identically on retry, so surfacing them
   // immediately is both more honest and avoids wasting the nudge budget.
-  function _isRecoverableStreamErr(err) {
-    if (!err) return false;
-    if (err.name === 'TypeError') return true;   // fetch/reader network failure
-    const m = (err.message || '').toLowerCase();
-    if (/\btool\b|unsupported|json|parse|\b4\d\d\b|\b5\d\d\b/.test(m)) return false;
-    return /network|fetch|connection|reset|closed|aborted|stream|tim(?:e|ed)\s?out|econn|eof/.test(m);
-  }
-
   function _tryAutoRecover(holder, accumulated, sessionId) {
     if (_autoNudges >= _AUTO_NUDGE_CAP) return false;
     _autoNudges++;
     if (holder && accumulated) {
       holder.dataset.raw = accumulated;
     }
-    _pendingContinue = holder || null;   // merge the continuation into the same bubble
+    // The server run is detached and keeps its exact pinned model/tool state.
-    _hideUserBubble = true;              // no user bubble for the handshake
+    // Reconnect to that run instead of submitting a new user turn, which would
-    _autoContinuePending = true;         // don't reset the counter on this submit
+    // cancel it, retry the selected model, and risk duplicating side effects.
-    const _abandon = () => {             // clear the pending flags so they can't
+    setTimeout(async () => {
-      _pendingContinue = null;           // leak into whatever chat is now open
-      _hideUserBubble = false;
-      _autoContinuePending = false;
-    };
-    // Defer so the stream's finally resets state first — otherwise the send
-    // button is still in "stop" mode and clicking it would toggle, not send.
-    setTimeout(() => {
       // The stream that died may not be the chat the user is now looking at —
-      // never inject the recovery handshake into the wrong conversation.
+      // never attach the recovery reader to the wrong conversation.
-      if (sessionId && sessionModule.getCurrentSessionId() !== sessionId) { _abandon(); return; }
+      if (sessionId && sessionModule.getCurrentSessionId() !== sessionId) return;
-      const msgInput = uiModule.el('message');
+      const resumed = await resumeStream(sessionId, holder || null);
-      const sb = document.querySelector('.send-btn');
+      if (!resumed && holder && holder.isConnected) {
-      if (!msgInput || !sb) { _abandon(); return; }
+        const body = holder.querySelector('.body');
-      const tail = (accumulated || '').slice(-400);
+        if (body) typewriterInto(body, 'Connection lost. The existing run could not be resumed.');
-      msgInput.value = tail
+      }
-        ? `The stream dropped before you finished. It ended with:\n\n${tail}\n\nIf the task is fully complete, reply with just: DONE. Otherwise continue exactly where you left off and finish it — do not repeat what you already wrote.`
-        : `The stream dropped before you produced anything. If the task is already done, reply with just: DONE. Otherwise complete it now.`;
-      sb.click();
     }, 200);
     return true;
   }
@@ -4545,9 +4848,13 @@ import {
     // view must stop all delayed rendering immediately. The reader loop may not
     // receive another SSE line for an arbitrary amount of time.
     if (active.cancelViewWork) active.cancelViewWork();
-    // Store background stream state
+
+    const terminalSaved = _terminalSavedStreams.has(sessionId);
+    // Store background stream state. A canonical terminal event can precede
+    // its SSE error event; preserve completion if the user switches sessions
+    // during that gap instead of creating a fresh running/error marker.
     _backgroundStreams.set(sessionId, {
-      status: 'running',
+      status: terminalSaved ? 'completed' : 'running',
       accumulated: currentAccumulated,
       sourcesHtml: '',
       findingsData: null,
@@ -4556,8 +4863,10 @@ import {
       metrics: null,
     });
     // Mark session with pulsing dot in sidebar
-    if (sessionModule && sessionModule.markStreaming) {
+    if (!terminalSaved && sessionModule && sessionModule.markStreaming) {
       sessionModule.markStreaming(sessionId);
+    } else if (terminalSaved && sessionModule && sessionModule.clearStreaming) {
+      sessionModule.clearStreaming(sessionId);
     }
     // Clear local state WITHOUT aborting the fetch
     if (currentAbort === active.abortCtrl) currentAbort = null;
@@ -4584,7 +4893,7 @@ import {
    * reloaded from the DB so its full render stays faithful. Returns true if it
    * attached, false to let the caller fall back to spinner+poll.
    */
-  export async function resumeStream(sessionId) {
+  export async function resumeStream(sessionId, replaceHolder = null) {
     if (!sessionId) return false;
     if (hasActiveStream(sessionId)) return false;
 
@@ -4595,9 +4904,12 @@ import {
       return false;
     }
     if (!res.ok || !res.body) return false;
+    const resumeRunId = res.headers.get('X-Odysseus-Run-Id') || '';
+    if (resumeRunId) _streamRunIds.set(sessionId, resumeRunId);
 
     const box = document.getElementById('chat-history');
     if (!box) return false;
+    if (replaceHolder && replaceHolder.parentNode) replaceHolder.remove();
 
     // Block duplicate re-attach attempts while this reader is live. A dedicated
     // set (not _backgroundStreams) so checkBackgroundStream doesn't mistake this
@@ -4612,6 +4924,8 @@ import {
     holder.innerHTML = '<div class="role">' + uiModule.esc(roleLabel) +
       ' <span class="role-timestamp">' + roleTs + '</span></div>' +
       '<div class="body"><div class="stream-content"></div></div>';
+    holder._requestedModel = meta && meta.model;
+    holder._actualModel = holder._requestedModel;
     _applyModelColor(holder.querySelector('.role'), meta && meta.model);
     const contentDiv = holder.querySelector('.stream-content');
     box.appendChild(holder);
@@ -4629,6 +4943,8 @@ import {
     let gotDelta = false;
     let leftSession = false;
     let metricsData = null;
+    let replayError = null;
+    let canonicalTerminalSeen = false;
     // "Rich" responses (tool calls, sources, doc streaming, multi-round) need the
     // full canonical render, which is rebuilt from the saved DB record on reload.
     // Plain text replies can be finalized in place without a reload.
@@ -4665,6 +4981,8 @@ import {
         const parts = buffer.split('\n\n');
         buffer = parts.pop();
         for (const part of parts) {
+          const eventIsError = part.split('\n').some(l => l.trim() === 'event: error');
+          if (eventIsError) rich = true;
           const line = part.split('\n').find(l => l.startsWith('data: '));
           if (!line) continue;
           const payload = line.slice(6);
@@ -4674,7 +4992,9 @@ import {
           }
           let json;
           try { json = JSON.parse(payload); } catch (_) { continue; }
-          if (json.delta) {
+          if (eventIsError) {
+            replayError = createTerminalStreamError(json);
+          } else if (json.delta) {
             roundText += json.delta;
             if (!docFenceOpened && (roundText.includes('```create_document\n') || roundText.includes('```document\n') || roundText.includes('```documen\n'))) {
               docFenceOpened = true;
@@ -4690,6 +5010,64 @@ import {
             if (documentModule) documentModule.streamDocDelta(json.content || json.delta || '');
           } else if (json.type === 'metrics') {
             metricsData = json.data || metricsData;
+            if (metricsData && resumeRunId) {
+              metricsData._costRecordId = _metricsCostRecordId(resumeRunId, json);
+            }
+            if (metricsData) {
+              chatRenderer.recordSessionMetricsCost(metricsData, sessionId);
+            }
+          } else if (json.type === 'fallback') {
+            // Replay can attach after the selected route has already failed.
+            // Reflect the fallback immediately, then reload the canonical
+            // multi-round record when the detached run completes.
+            rich = true;
+            const fallbackHolder = applyModelRouteEventState(json, holder, null, meta && meta.model);
+            if (fallbackHolder) {
+              _setRoleModelLabel(
+                fallbackHolder.querySelector('.role'),
+                fallbackHolder._requestedModel,
+                fallbackHolder._actualModel,
+                {
+                  reason: json.reason,
+                  requestedEndpointId: fallbackHolder._requestedEndpointId,
+                  requestedEndpointLabel: fallbackHolder._requestedEndpointLabel,
+                  actualEndpointId: fallbackHolder._actualEndpointId,
+                  actualEndpointLabel: fallbackHolder._actualEndpointLabel,
+                },
+              );
+            }
+            uiModule.showToast(
+              'Fallback: ' + _shortModel(json.selected_model || '') + ' failed — answered by ' +
+              _shortModel(json.answered_by || ''),
+              6000,
+            );
+          } else if (json.type === 'model_actual') {
+            rich = true;
+            const modelHolder = applyModelRouteEventState(json, holder, null, meta && meta.model);
+            if (modelHolder) {
+              _setRoleModelLabel(
+                modelHolder.querySelector('.role'),
+                modelHolder._requestedModel,
+                modelHolder._actualModel,
+                {
+                  requestedEndpointId: modelHolder._requestedEndpointId,
+                  requestedEndpointLabel: modelHolder._requestedEndpointLabel,
+                  actualEndpointId: modelHolder._actualEndpointId,
+                  actualEndpointLabel: modelHolder._actualEndpointLabel,
+                },
+              );
+            }
+          } else if (json.type === 'agent_terminal' || json.type === 'chat_terminal') {
+            // The server has already persisted canonical partial content plus
+            // a sanitized failure note and actual route provenance.  Do not
+            // finalize replayed deltas as a successful local-only answer.
+            rich = true;
+            canonicalTerminalSeen = true;
+            metricsData = json.data || metricsData;
+            if (metricsData && resumeRunId) {
+              metricsData._costRecordId = _metricsCostRecordId(resumeRunId, json);
+            }
+            if (metricsData) displayMetrics(holder, metricsData);
           } else if (json.type === 'tool_start' || json.type === 'tool_output' ||
                      json.type === 'tool_progress' || json.type === 'agent_step' ||
                      json.type === 'web_sources' || json.type === 'rag_sources' ||
@@ -4700,7 +5078,8 @@ import {
         }
       }
     } catch (e) {
-      // Network drop or parse failure: fall through to the reload below.
+      // Network drop or parse failure: fall through to the canonical reload.
+      rich = true;
     }
 
     cleanup();
@@ -4710,6 +5089,18 @@ import {
     const onThisSession = sessionModule.getCurrentSessionId &&
                           sessionModule.getCurrentSessionId() === sessionId;
 
+    // A failure before substantive output has no persisted assistant record to
+    // recover through a canonical reload. Keep its sanitized provider/request
+    // error visible in the replay holder instead of deleting the only evidence.
+    if (onThisSession && replayError && !canonicalTerminalSeen) {
+      const errorDiv = document.createElement('div');
+      errorDiv.style.cssText = 'color: var(--color-error); font-style: italic; padding: 4px 0;';
+      errorDiv.textContent = `[Error: ${replayError.message}]`;
+      contentDiv.appendChild(errorDiv);
+      uiModule.scrollHistory();
+      return true;
+    }
+
     // Plain text reply: finalize in place. Replace the live bubble with a
     // canonical single message (markdown + footer actions + metrics) using the
     // same renderer history does. No history refetch, no end-of-stream flicker.
@@ -4726,6 +5117,9 @@ import {
     // reload from the DB for the full canonical render.
     if (holder._docWritingThread && holder._docWritingThread.parentNode) holder._docWritingThread.remove();
     if (holder.parentNode) holder.remove();
+    if (metricsData) {
+      chatRenderer.recordSessionMetricsCost(metricsData, sessionId);
+    }
     if (onThisSession) sessionModule.selectSession(sessionId);
     else sessionModule.loadSessions();
     return true;

static/js/chatModelProvenance.js

@@ -0,0 +1,104 @@
+/** Select and update the response holder for a route-provenance event. */
+export function applyModelRouteEventState(event, holder, roundHolder, defaultModel = '') {
+  const target = event && event.round && roundHolder ? roundHolder : holder;
+  if (!target) return null;
+
+  target._requestedModel = (
+    event.requested_model
+    || event.selected_model
+    || target._requestedModel
+    || defaultModel
+  );
+  target._actualModel = (
+    event.model
+    || event.answered_by
+    || target._actualModel
+    || target._requestedModel
+  );
+  const hasEndpointRoute = Boolean(
+    event.requested_endpoint_id
+    || event.selected_endpoint_id
+    || event.endpoint_id
+    || event.answered_by_endpoint_id
+    || event.requested_endpoint_label
+    || event.selected_endpoint_label
+    || event.endpoint_label
+    || event.answered_by_endpoint_label
+    || target._requestedEndpointLabel
+  );
+  if (hasEndpointRoute) {
+    target._requestedEndpointId = (
+      event.requested_endpoint_id
+      || event.selected_endpoint_id
+      || target._requestedEndpointId
+      || null
+    );
+    target._requestedEndpointLabel = (
+      event.requested_endpoint_label
+      || event.selected_endpoint_label
+      || target._requestedEndpointLabel
+      || 'Selected route'
+    );
+    target._actualEndpointId = (
+      event.endpoint_id
+      || event.answered_by_endpoint_id
+      || target._actualEndpointId
+      || target._requestedEndpointId
+      || null
+    );
+    target._actualEndpointLabel = (
+      event.endpoint_label
+      || event.answered_by_endpoint_label
+      || target._actualEndpointLabel
+      || target._requestedEndpointLabel
+    );
+  }
+  return target;
+}
+
+/** Copy the active route into the bubble created for the next Agent round. */
+export function inheritModelRouteState(holder, roundHolder, target, defaultModel = '') {
+  if (!target) return null;
+  const source = roundHolder || holder;
+  target._requestedModel = source?._requestedModel || defaultModel;
+  target._actualModel = source?._actualModel || target._requestedModel;
+  if (source?._requestedEndpointLabel || source?._actualEndpointLabel) {
+    target._requestedEndpointId = source?._requestedEndpointId || null;
+    target._requestedEndpointLabel = source?._requestedEndpointLabel || 'Selected route';
+    target._actualEndpointId = source?._actualEndpointId || target._requestedEndpointId;
+    target._actualEndpointLabel = source?._actualEndpointLabel || target._requestedEndpointLabel;
+  }
+  return target;
+}
+
+/** Apply final/metrics provenance to the active round, not the first bubble. */
+export function applyModelMetricsState(metrics, holder, roundHolder, defaultModel = '') {
+  const target = roundHolder || holder;
+  if (!target || !metrics) return target || null;
+  const roundModels = Array.isArray(metrics.round_models) ? metrics.round_models : [];
+  const roundModel = roundHolder && roundModels.length
+    ? roundModels[roundModels.length - 1]
+    : null;
+  target._requestedModel = metrics.requested_model || target._requestedModel || defaultModel;
+  target._actualModel = roundModel || metrics.model || target._actualModel || target._requestedModel;
+  const roundEndpointIds = Array.isArray(metrics.round_endpoint_ids) ? metrics.round_endpoint_ids : [];
+  const roundEndpointLabels = Array.isArray(metrics.round_endpoint_labels) ? metrics.round_endpoint_labels : [];
+  if (
+    metrics.requested_endpoint_label
+    || metrics.endpoint_label
+    || roundEndpointLabels.length
+    || target._requestedEndpointLabel
+  ) {
+    target._requestedEndpointId = metrics.requested_endpoint_id || target._requestedEndpointId || null;
+    target._requestedEndpointLabel = metrics.requested_endpoint_label || target._requestedEndpointLabel || 'Selected route';
+    const hasRoundEndpointId = Boolean(roundHolder && roundEndpointIds.length);
+    const hasRoundEndpointLabel = Boolean(roundHolder && roundEndpointLabels.length);
+    target._actualEndpointId = hasRoundEndpointId
+      ? roundEndpointIds[roundEndpointIds.length - 1]
+      : (metrics.endpoint_id || target._actualEndpointId || target._requestedEndpointId);
+    target._actualEndpointLabel = hasRoundEndpointLabel
+      ? roundEndpointLabels[roundEndpointLabels.length - 1]
+      : (metrics.endpoint_label || target._actualEndpointLabel || target._requestedEndpointLabel);
+  }
+  return target;
+}

static/js/chatRenderer.js

@@ -615,10 +615,36 @@ export function sameModelName(left, right) {
     || shortModel(a).toLowerCase() === shortModel(b).toLowerCase();
 }
 
-export function modelRouteLabel(requestedModel, actualModel) {
+function shortEndpointLabel(label) {
+  const value = modelValue(label);
+  if (!value) return '';
+  return value.length > 18 ? value.slice(0, 17) + '…' : value;
+}
+
+export function modelRouteLabel(
+  requestedModel,
+  actualModel,
+  requestedEndpointLabel = '',
+  actualEndpointLabel = '',
+  requestedEndpointId = '',
+  actualEndpointId = '',
+) {
   const requested = modelValue(requestedModel);
   const actual = modelValue(actualModel) || requested;
-  if (!requested || sameModelName(requested, actual)) return shortModel(actual || requested);
+  const requestedRoute = modelValue(requestedEndpointId || requestedEndpointLabel);
+  const actualRoute = modelValue(actualEndpointId || actualEndpointLabel);
+  const routeChanged = Boolean(
+    actualRoute
+    && requestedRoute
+    && actualRoute !== requestedRoute
+  );
+  if (!requested || sameModelName(requested, actual)) {
+    const model = shortModel(actual || requested);
+    if (!routeChanged) return model;
+    const from = shortEndpointLabel(requestedEndpointLabel || 'Selected route');
+    const to = shortEndpointLabel(actualEndpointLabel || actualEndpointId);
+    return model + ' (' + from + ' -> ' + to + ')';
+  }
   return shortModel(requested) + ' -> ' + shortModel(actual);
 }
 
@@ -629,10 +655,24 @@ export function replyModelPair(modelName, metadata) {
   if (actualFromMeta || requestedFromMeta) {
     const actual = actualFromMeta || requestedFromMeta || modelValue(modelName);
     const requested = requestedFromMeta || actual;
-    return { requestedModel: requested, actualModel: actual };
+    return {
+      requestedModel: requested,
+      actualModel: actual,
+      requestedEndpointId: meta.requested_endpoint_id || null,
+      requestedEndpointLabel: meta.requested_endpoint_label || 'Selected route',
+      actualEndpointId: meta.endpoint_id || null,
+      actualEndpointLabel: meta.endpoint_label || meta.requested_endpoint_label || 'Selected route',
+    };
   }
   const fallback = modelValue(modelName);
-  return { requestedModel: fallback, actualModel: fallback };
+  return {
+    requestedModel: fallback,
+    actualModel: fallback,
+    requestedEndpointId: null,
+    requestedEndpointLabel: 'Selected route',
+    actualEndpointId: null,
+    actualEndpointLabel: 'Selected route',
+  };
 }
 
 /**
@@ -824,12 +864,50 @@ export function isCostTrackedEndpoint(url) {
 }
 
 /** Cost for the current turn, returning null for non-billable endpoints. */
-function _billableCost(model, inputTokens, outputTokens) {
+function _billableCost(model, inputTokens, outputTokens, endpointCostTracked, selectedEndpointUrl) {
-  const url = _currentEndpointUrl();
+  // Foreground fallback can answer on a different endpoint than the session's
-  if (!isCostTrackedEndpoint(url)) return null;
+  // selected route. Prefer the backend's non-secret actual-route
+  // classification; retain the selected-endpoint check for older history.
+  if (endpointCostTracked === false) return null;
+  const selectedUrl = selectedEndpointUrl === undefined
+    ? _currentEndpointUrl()
+    : selectedEndpointUrl;
+  if (endpointCostTracked !== true && !isCostTrackedEndpoint(selectedUrl)) {
+    return null;
+  }
   return getModelCost(model, inputTokens, outputTokens);
 }
 
+/** Sum cost using the route/model that produced each Agent round. */
+function _metricsBillableCost(metrics, model, inputTokens, outputTokens, selectedEndpointUrl) {
+  const buckets = Array.isArray(metrics.usage_buckets) ? metrics.usage_buckets : [];
+  if (!buckets.length) {
+    return _billableCost(
+      model,
+      inputTokens,
+      outputTokens,
+      metrics.endpoint_cost_tracked,
+      selectedEndpointUrl,
+    );
+  }
+  let total = 0;
+  let hasPricedUsage = false;
+  for (const bucket of buckets) {
+    if (!bucket || typeof bucket !== 'object') continue;
+    const bucketCost = _billableCost(
+      bucket.model || model,
+      Number(bucket.input_tokens) || 0,
+      Number(bucket.output_tokens) || 0,
+      bucket.endpoint_cost_tracked,
+      selectedEndpointUrl,
+    );
+    if (bucketCost === null) continue;
+    total += bucketCost;
+    hasPricedUsage = true;
+  }
+  return hasPricedUsage ? total : null;
+}
+
 export function getImageCost(model, quality, size) {
   if (!model) return null;
   const m = model.toLowerCase();
@@ -844,6 +922,9 @@ export function getImageCost(model, quality, size) {
 
 /* ── Session cost helpers ─────────────────────────────────────────── */
 const _COST_KEY = 'ody-session-cost';
+const _COST_RUNS_KEY = 'ody-session-cost-runs';
+const _MAX_COST_RUNS_PER_SESSION = 256;
+const _COST_LEDGER_LOCK = 'odysseus-session-cost-ledger';
 
 /** Return the accumulated cost for the current (or given) session. */
 export function getSessionCost(sessionId) {
@@ -851,7 +932,14 @@ export function getSessionCost(sessionId) {
   if (!sid) return 0;
   try {
     const costs = JSON.parse(localStorage.getItem(_COST_KEY) || '{}');
-    return costs[sid] || 0;
+    const runCosts = JSON.parse(localStorage.getItem(_COST_RUNS_KEY) || '{}');
+    const recordedRuns = runCosts[sid] && typeof runCosts[sid] === 'object'
+      ? Object.values(runCosts[sid])
+      : [];
+    return (costs[sid] || 0) + recordedRuns.reduce(
+      (total, value) => total + (Number(value) || 0),
+      0,
+    );
   } catch (_e) { return 0; }
 }
 
@@ -863,6 +951,9 @@ export function resetSessionCost(sessionId) {
     const costs = JSON.parse(localStorage.getItem(_COST_KEY) || '{}');
     delete costs[sid];
     localStorage.setItem(_COST_KEY, JSON.stringify(costs));
+    const runCosts = JSON.parse(localStorage.getItem(_COST_RUNS_KEY) || '{}');
+    delete runCosts[sid];
+    localStorage.setItem(_COST_RUNS_KEY, JSON.stringify(runCosts));
   } catch (_e) { /* ignore */ }
   updateSessionCostUI();
 }
@@ -871,21 +962,8 @@ export function resetSessionCost(sessionId) {
 export function updateSessionCostUI() {
   const el = document.getElementById('session-cost-display');
   if (!el) return;
-  // Non-billable endpoint? Hide the badge and clear stale cost that a previous
+  // The ledger records billable work already performed in this session. A
-  // cloud-rate calculation may have left in localStorage for this session.
+  // selected local endpoint does not erase cost from a paid fallback route.
-  const _url = _currentEndpointUrl();
-  if (!isCostTrackedEndpoint(_url)) {
-    const sid = window.sessionModule && window.sessionModule.getCurrentSessionId();
-    if (sid && getSessionCost(sid) > 0) {
-      try {
-        const costs = JSON.parse(localStorage.getItem(_COST_KEY) || '{}');
-        delete costs[sid];
-        localStorage.setItem(_COST_KEY, JSON.stringify(costs));
-      } catch (_e) { /* ignore */ }
-    }
-    el.style.display = 'none';
-    return;
-  }
   const cost = getSessionCost();
   if (cost > 0) {
     el.textContent = '$' + (cost < 0.01 ? cost.toFixed(4) : cost < 1 ? cost.toFixed(3) : cost.toFixed(2));
@@ -895,6 +973,94 @@ export function updateSessionCostUI() {
   }
 }
 
+/** Record one metrics payload in a session ledger at most once. */
+export function recordSessionMetricsCost(metrics, sessionId, selectedEndpointUrl) {
+  if (!metrics || typeof metrics !== 'object') return null;
+  const cost = _metricsBillableCost(
+    metrics,
+    metrics.model || 'Unknown',
+    metrics.input_tokens || 0,
+    metrics.output_tokens || 0,
+    selectedEndpointUrl,
+  );
+  if (metrics._fromHistory) return cost;
+  const sid = sessionId || (
+    window.sessionModule && window.sessionModule.getCurrentSessionId()
+  );
+  if (!sid || cost === null) return cost;
+  const runId = typeof metrics._costRecordId === 'string'
+    ? metrics._costRecordId.trim()
+    : '';
+  if ((metrics._costRecorded || metrics._costRecordPending) && !runId) return cost;
+  // Recorded is only set once the write actually runs; pending covers the
+  // window while the write waits on the cross-tab lock, so a replay in that
+  // window cannot double-add and a tab closed mid-queue never claims recorded.
+  metrics._costRecordPending = true;
+  const writeCost = () => {
+    if (runId) {
+      try {
+        const runCosts = JSON.parse(localStorage.getItem(_COST_RUNS_KEY) || '{}');
+        const sessionRuns = runCosts[sid] && typeof runCosts[sid] === 'object'
+          ? runCosts[sid]
+          : {};
+        // Assigning by detached-run identity is replay-idempotent even when a
+        // refresh produces a fresh metrics object. The Web Lock around this
+        // read/modify/write also keeps distinct runs from two tabs from
+        // overwriting one another's stale snapshot.
+        sessionRuns[runId] = cost;
+        const entries = Object.entries(sessionRuns);
+        if (entries.length > _MAX_COST_RUNS_PER_SESSION) {
+          const overflow = entries.slice(0, entries.length - _MAX_COST_RUNS_PER_SESSION);
+          const costs = JSON.parse(localStorage.getItem(_COST_KEY) || '{}');
+          costs[sid] = (costs[sid] || 0) + overflow.reduce(
+            (total, entry) => total + (Number(entry[1]) || 0),
+            0,
+          );
+          overflow.forEach(([oldRunId]) => delete sessionRuns[oldRunId]);
+          localStorage.setItem(_COST_KEY, JSON.stringify(costs));
+        }
+        runCosts[sid] = sessionRuns;
+        localStorage.setItem(_COST_RUNS_KEY, JSON.stringify(runCosts));
+      } catch (_e) { /* ignore */ }
+    } else {
+      try {
+        const costs = JSON.parse(localStorage.getItem(_COST_KEY) || '{}');
+        costs[sid] = (costs[sid] || 0) + cost;
+        localStorage.setItem(_COST_KEY, JSON.stringify(costs));
+      } catch (_e) { /* ignore */ }
+    }
+    metrics._costRecorded = true;
+    metrics._costRecordPending = false;
+    const currentSid = window.sessionModule && window.sessionModule.getCurrentSessionId();
+    if (currentSid === sid) updateSessionCostUI();
+  };
+
+  let writeStarted = false;
+  const guardedWrite = () => {
+    writeStarted = true;
+    writeCost();
+  };
+  try {
+    if (
+      typeof navigator !== 'undefined'
+      && navigator.locks
+      && typeof navigator.locks.request === 'function'
+    ) {
+      const pendingWrite = navigator.locks.request(_COST_LEDGER_LOCK, guardedWrite);
+      if (pendingWrite && typeof pendingWrite.catch === 'function') {
+        pendingWrite.catch(() => {
+          if (!writeStarted) guardedWrite();
+        });
+      }
+    } else {
+      guardedWrite();
+    }
+  } catch (_e) {
+    if (!writeStarted) guardedWrite();
+  }
+  return cost;
+}
+
 /** Create a timestamp span for role labels.
  * Pass an ISO string / Date / epoch-ms to render the message's own time
  * (used when replaying history). Falls back to "now" when no value is given. */
@@ -1874,23 +2040,19 @@ export function displayMetrics(messageElement, metrics) {
   const isReal = metrics.usage_source === 'real';
   const ctxPct = metrics.context_percent;
   const model = metrics.model || 'Unknown';
-  const cost = _billableCost(model, inputTokens, outputTokens);
+  const cost = _metricsBillableCost(
+    metrics,
+    model,
+    inputTokens,
+    outputTokens,
+  );
 
   // Nothing useful to show — bail out (only if ALL metrics are missing)
   if (!responseTime && !inputTokens && !outputTokens && tps == null && !ctxPct) return;
 
-  // Accumulate session cost (only on fresh metrics, not history reload)
+  // Rendering can occur when metrics arrive and again after [DONE]. The
-  if (!metrics._fromHistory) {
+  // ledger mutation is idempotent for that shared payload.
-    const _sid = window.sessionModule && window.sessionModule.getCurrentSessionId();
+  recordSessionMetricsCost(metrics);
-    if (_sid && cost !== null) {
-      try {
-        const _costs = JSON.parse(localStorage.getItem(_COST_KEY) || '{}');
-        _costs[_sid] = (_costs[_sid] || 0) + cost;
-        localStorage.setItem(_COST_KEY, JSON.stringify(_costs));
-      } catch (_e) { /* ignore */ }
-      updateSessionCostUI();
-    }
-  }
 
   // Keep token counts in the Message Stats popup; the footer should stay slim.
   const costStr0 = cost !== null ? `$${cost < 0.01 ? cost.toFixed(4) : cost.toFixed(3)}` : null;
@@ -2307,9 +2469,19 @@ export function addMessage(role, content, modelName, metadata) {
     const textRaw = Array.isArray(content) ? markdownModule.renderContent(content) : content;
 
     // --- Agent multi-bubble reconstruction from saved metadata ---
-    if (role === 'assistant' && metadata && metadata.tool_events && metadata.tool_events.length > 0) {
+    if (
+      role === 'assistant'
+      && metadata
+      && (
+        (Array.isArray(metadata.tool_events) && metadata.tool_events.length > 0)
+        || (Array.isArray(metadata.round_texts) && metadata.round_texts.length > 1)
+      )
+    ) {
       const roundTexts = metadata.round_texts || [];
-      const toolEvents = metadata.tool_events;
+      const roundModels = metadata.round_models || [];
+      const roundEndpointIds = metadata.round_endpoint_ids || [];
+      const roundEndpointLabels = metadata.round_endpoint_labels || [];
+      const toolEvents = metadata.tool_events || [];
       let pendingAskUser = null;
       let lastWrap = null;
       let firstMsgAi = null;
@@ -2322,7 +2494,8 @@ export function addMessage(role, content, modelName, metadata) {
         toolsByRound[r].push(ev);
       }
 
-      const maxRound = Math.max(...Object.keys(toolsByRound).map(Number), roundTexts.length);
+      const toolRounds = Object.keys(toolsByRound).map(Number);
+      const maxRound = Math.max(toolRounds.length ? Math.max(...toolRounds) : 0, roundTexts.length);
 
       for (let r = 0; r < maxRound; r++) {
         const roundNum = r + 1;
@@ -2334,10 +2507,31 @@ export function addMessage(role, content, modelName, metadata) {
           const roleEl = document.createElement('div');
           roleEl.className = 'role';
           const pair = replyModelPair(modelName, metadata);
-          const contModel = pair.actualModel || pair.requestedModel;
+          const contModel = roundModels[r] || pair.actualModel || pair.requestedModel;
-          roleEl.textContent = modelRouteLabel(pair.requestedModel, contModel);
+          const contEndpointId = r < roundEndpointIds.length
-          if (pair.requestedModel && contModel && !sameModelName(pair.requestedModel, contModel)) {
+            ? roundEndpointIds[r]
-            roleEl.title = pair.requestedModel + ' -> ' + contModel;
+            : pair.actualEndpointId;
+          const contEndpointLabel = r < roundEndpointLabels.length
+            ? roundEndpointLabels[r]
+            : pair.actualEndpointLabel;
+          roleEl.textContent = modelRouteLabel(
+            pair.requestedModel,
+            contModel,
+            pair.requestedEndpointLabel,
+            contEndpointLabel,
+            pair.requestedEndpointId,
+            contEndpointId,
+          );
+          if (
+            pair.requestedModel
+            && contModel
+            && (
+              !sameModelName(pair.requestedModel, contModel)
+              || (pair.requestedEndpointId && contEndpointId && pair.requestedEndpointId !== contEndpointId)
+            )
+          ) {
+            roleEl.title = pair.requestedModel + ' -> ' + contModel
+              + ' (' + pair.requestedEndpointLabel + ' -> ' + contEndpointLabel + ')';
           }
           applyModelColor(roleEl, contModel);
           if (r === 0) roleEl.appendChild(roleTimestamp(metadata?.timestamp));
@@ -2492,7 +2686,14 @@ export function addMessage(role, content, modelName, metadata) {
     const isCompacted = metadata?.compacted;
     const replyModels = replyModelPair(modelName, metadata);
     const resolvedModel = replyModels.actualModel || replyModels.requestedModel;
-    var _roleText = role === 'user' ? 'You' : (isSlash || isCompacted) ? 'Odysseus' : modelRouteLabel(replyModels.requestedModel, resolvedModel);
+    var _roleText = role === 'user' ? 'You' : (isSlash || isCompacted) ? 'Odysseus' : modelRouteLabel(
+      replyModels.requestedModel,
+      resolvedModel,
+      replyModels.requestedEndpointLabel,
+      replyModels.actualEndpointLabel,
+      replyModels.requestedEndpointId,
+      replyModels.actualEndpointId,
+    );
     if (role === 'assistant' && (metadata?.research || metadata?.research_clarification)) {
       _roleText += ' (Research)';
     }
@@ -2503,8 +2704,14 @@ export function addMessage(role, content, modelName, metadata) {
     }
     r.textContent = _roleText;
     if (role !== 'user') {
-      if (!isSlash && !isCompacted && replyModels.requestedModel && resolvedModel && !sameModelName(replyModels.requestedModel, resolvedModel)) {
+      const endpointChanged = Boolean(
-        r.title = replyModels.requestedModel + ' -> ' + resolvedModel;
+        replyModels.requestedEndpointId
+        && replyModels.actualEndpointId
+        && replyModels.requestedEndpointId !== replyModels.actualEndpointId
+      );
+      if (!isSlash && !isCompacted && replyModels.requestedModel && resolvedModel && (!sameModelName(replyModels.requestedModel, resolvedModel) || endpointChanged)) {
+        r.title = replyModels.requestedModel + ' -> ' + resolvedModel
+          + ' (' + replyModels.requestedEndpointLabel + ' -> ' + replyModels.actualEndpointLabel + ')';
       }
       if (!isSlash && !isCompacted) applyModelColor(r, resolvedModel);
       r.appendChild(roleTimestamp(metadata?.timestamp));
@@ -2788,6 +2995,7 @@ const chatRenderer = {
   getSessionCost,
   resetSessionCost,
   updateSessionCostUI,
+  recordSessionMetricsCost,
   roleTimestamp,
   stripToolBlocks,
   copyMessageText,

static/js/chatStreamErrors.js

@@ -0,0 +1,23 @@
+/** Build a terminal stream error while preserving provider-supplied text. */
+export function createTerminalStreamError(payload = {}) {
+  const rawError = payload.error;
+  const message = (
+    payload.text
+    || (typeof rawError === 'string' ? rawError : rawError?.message)
+    || `Error ${payload.status || 'unknown'}`
+  );
+  const error = new Error(message);
+  error.name = 'TerminalStreamError';
+  error.terminalStreamError = true;
+  error.status = payload.status;
+  return error;
+}
+
+/** Only connection-class stream failures are safe to resubmit automatically. */
+export function isRecoverableStreamError(error) {
+  if (!error || error.terminalStreamError || error.name === 'TerminalStreamError') return false;
+  if (error.name === 'TypeError') return true;
+  const message = (error.message || '').toLowerCase();
+  if (/\btool\b|unsupported|json|parse|\b4\d\d\b|\b5\d\d\b/.test(message)) return false;
+  return /network|fetch|connection|reset|closed|aborted|stream|tim(?:e|ed)\s?out|econn|eof/.test(message);
+}

static/js/settings.js

@@ -445,14 +445,7 @@ async function initDefaultChat() {
   var epSel = el('set-defaultEpSelect');
   var modelSel = el('set-defaultModelSelect');
   var msg = el('set-defaultChatMsg');
-  var fbContainer = el('set-defaultFallbacks');
-  var addFbBtn = el('set-defaultAddFallback');
   var _endpoints = [];
-  var _fallbacks = []; // Hidden legacy DOM hook; stored values are not loaded or saved.
-
-  function enabledEndpoints() {
-    return _endpoints.filter(function(e) { return e.is_enabled; });
-  }
 
   // Fill any <select> with the models for a given endpoint id.
   function fillModels(selectEl, epId, selected) {
@@ -469,64 +462,6 @@ async function initDefaultChat() {
   function refreshEndpointOptions(selectedEndpoint, selectedModel) {
     _fillEndpointSelect(epSel, _endpoints, selectedEndpoint !== undefined ? selectedEndpoint : epSel.value, false);
     refreshModels(selectedModel !== undefined ? selectedModel : modelSel.value);
-    renderFallbacks();
-  }
-
-  // Render the fallback chain. Each row is endpoint + model + remove.
-  function renderFallbacks() {
-    fbContainer.innerHTML = '';
-    _fallbacks.forEach(function(fb, idx) {
-      var row = document.createElement('div');
-      row.className = 'settings-fallback-row';
-
-      var num = document.createElement('span');
-      num.className = 'settings-fallback-num';
-      num.textContent = (idx + 1) + '.';
-
-      var epS = document.createElement('select');
-      epS.className = 'settings-select';
-      enabledEndpoints().forEach(function(ep) {
-        var o = document.createElement('option');
-        o.value = ep.id;
-        o.textContent = ep.name + (ep.online ? '' : ' (offline)');
-        epS.appendChild(o);
-      });
-      var first = enabledEndpoints()[0];
-      epS.value = fb.endpoint_id || (first ? first.id : '');
-
-      var mS = document.createElement('select');
-      mS.className = 'settings-select';
-      fillModels(mS, epS.value, fb.model);
-
-      // Keep the model in sync with the values actually shown.
-      fb.endpoint_id = epS.value;
-      fb.model = mS.value;
-
-      epS.addEventListener('change', function() {
-        fb.endpoint_id = epS.value;
-        fillModels(mS, epS.value, '');
-        fb.model = mS.value;
-        saveDefault();
-      });
-      mS.addEventListener('change', function() { fb.model = mS.value; saveDefault(); });
-
-      var rm = document.createElement('button');
-      rm.type = 'button';
-      rm.className = 'settings-fallback-remove';
-      rm.title = 'Remove fallback';
-      rm.innerHTML = '<svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><polyline points="3 6 5 6 21 6"/><path d="M19 6l-1 14a2 2 0 0 1-2 2H8a2 2 0 0 1-2-2L5 6"/><path d="M10 11v6"/><path d="M14 11v6"/><path d="M9 6V4a1 1 0 0 1 1-1h4a1 1 0 0 1 1 1v2"/></svg>';
-      rm.addEventListener('click', function() {
-        _fallbacks.splice(idx, 1);
-        renderFallbacks();
-        saveDefault();
-      });
-
-      row.appendChild(num);
-      row.appendChild(epS);
-      row.appendChild(mS);
-      row.appendChild(rm);
-      fbContainer.appendChild(row);
-    });
   }
 
   try {
@@ -534,7 +469,6 @@ async function initDefaultChat() {
     var settings = await res.json();
     if (settings.default_endpoint_id) epSel.value = settings.default_endpoint_id;
     refreshModels(settings.default_model || '');
-    renderFallbacks();
   } catch (e) { console.warn('Failed to load default chat settings', e); }
 
   epSel.addEventListener('change', function() { refreshModels(''); saveDefault(); });
@@ -554,13 +488,6 @@ async function initDefaultChat() {
     } catch (e) { msg.textContent = 'Failed to save'; msg.style.color = 'var(--red)'; }
   }
 
-  if (addFbBtn) addFbBtn.addEventListener('click', function() {
-    var first = enabledEndpoints()[0];
-    _fallbacks.push({ endpoint_id: first ? first.id : '', model: '' });
-    renderFallbacks();
-    saveDefault();
-  });
-
   _registerAiEndpointRefresh(function(endpoints) {
     _endpoints = endpoints;
     refreshEndpointOptions(epSel.value, modelSel.value);

static/js/slashCommands.js

@@ -2027,12 +2027,12 @@ async function _cmdUsage(args, ctx) {
   const messageCount = Number(session?.message_count || 0);
   const totalTokens = Number(session?.total_tokens || 0);
   const costTracked = chatRenderer.isCostTrackedEndpoint ? chatRenderer.isCostTrackedEndpoint(endpointUrl) : true;
-  const cost = costTracked && chatRenderer.getSessionCost ? Number(chatRenderer.getSessionCost(sid) || 0) : 0;
+  const cost = chatRenderer.getSessionCost ? Number(chatRenderer.getSessionCost(sid) || 0) : 0;
-  const costLine = costTracked
+  const costLine = cost > 0
-    ? (cost > 0
     ? `Estimated local cost: $${cost < 0.01 ? cost.toFixed(4) : cost.toFixed(3)}`
-      : 'Estimated local cost: unavailable or zero')
+    : costTracked
-    : 'Estimated local cost: not tracked for this endpoint';
+      ? 'Estimated local cost: unavailable or zero'
+      : 'Estimated local cost: no billable usage recorded';
 
   slashReply(`<pre>${[
     `Session: ${ctx.esc(session?.name || 'Current chat')}`,

tests/test_agent_loop.py

@@ -314,17 +314,21 @@ class TestComputeFinalMetrics:
     def test_tool_events_included(self):
         events = [{"tool": "bash", "duration": 1.0}]
         texts = ["round 1 text"]
+        models = ["round-1-model"]
         m = _compute_final_metrics(**self._base_args(
             tool_events=events,
             round_texts=texts,
+            round_models=models,
         ))
         assert m["tool_events"] == events
         assert m["round_texts"] == texts
+        assert m["round_models"] == models
 
     def test_no_tool_events_excluded(self):
         m = _compute_final_metrics(**self._base_args(tool_events=[], round_texts=[]))
         assert "tool_events" not in m
         assert "round_texts" not in m
+        assert "round_models" not in m
 
 
 # ---------------------------------------------------------------------------

tests/test_agent_round_model_provenance_ui.py

@@ -0,0 +1,237 @@
+"""Saved Agent rounds must render and bill with actual per-round provenance."""
+
+import json
+from pathlib import Path
+import re
+import shutil
+import subprocess
+
+import pytest
+
+
+_SOURCE = (
+    Path(__file__).resolve().parents[1] / "static" / "js" / "chatRenderer.js"
+).read_text(encoding="utf-8")
+_CHAT_SOURCE = (
+    Path(__file__).resolve().parents[1] / "static" / "js" / "chat.js"
+).read_text(encoding="utf-8")
+_SLASH_SOURCE = (
+    Path(__file__).resolve().parents[1] / "static" / "js" / "slashCommands.js"
+).read_text(encoding="utf-8")
+_HAS_NODE = shutil.which("node") is not None
+
+
+def _function_source(name):
+    match = re.search(
+        rf"^(?:export )?function {name}\(.*?^\}}",
+        _SOURCE,
+        re.MULTILINE | re.DOTALL,
+    )
+    assert match, f"{name} not found"
+    return match.group(0).replace("export function", "function", 1)
+
+
+def _run_node(source):
+    proc = subprocess.run(
+        ["node", "--input-type=module"],
+        input=source,
+        capture_output=True,
+        text=True,
+        timeout=30,
+    )
+    assert proc.returncode == 0, proc.stderr
+    return json.loads(proc.stdout.strip())
+
+
+def test_saved_agent_rounds_prefer_round_model_provenance():
+    assert "const roundModels = metadata.round_models || [];" in _SOURCE
+    assert "const contModel = roundModels[r] || pair.actualModel || pair.requestedModel;" in _SOURCE
+    assert "Array.isArray(metadata.round_texts) && metadata.round_texts.length > 1" in _SOURCE
+    assert "const roundEndpointIds = metadata.round_endpoint_ids || [];" in _SOURCE
+    assert "const roundEndpointLabels = metadata.round_endpoint_labels || [];" in _SOURCE
+    assert "r < roundEndpointIds.length" in _SOURCE
+    assert "r < roundEndpointLabels.length" in _SOURCE
+    assert "roundEndpointIds[r] || pair.actualEndpointId" not in _SOURCE
+
+
+def test_metrics_cost_uses_actual_fallback_endpoint_classification():
+    assert "metrics.endpoint_cost_tracked" in _SOURCE
+    assert "endpointCostTracked === false" in _SOURCE
+    assert "endpointCostTracked !== true && !isCostTrackedEndpoint(selectedUrl)" in _SOURCE
+    assert "Array.isArray(metrics.usage_buckets)" in _SOURCE
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_agent_usage_buckets_sum_only_billable_answering_routes():
+    source = "\n".join([
+        "let currentUrl = '';",
+        "function _currentEndpointUrl() { return currentUrl; }",
+        "function isCostTrackedEndpoint(url) { return url === 'paid'; }",
+        "function getModelCost(_model, inputTokens, outputTokens) { return (inputTokens + outputTokens) / 1000; }",
+        _function_source("_billableCost"),
+        _function_source("_metricsBillableCost"),
+        "const paidSelected = {usage_buckets: [",
+        "  {model: 'selected', input_tokens: 100, output_tokens: 10, endpoint_cost_tracked: true},",
+        "  {model: 'local-fallback', input_tokens: 200, output_tokens: 20, endpoint_cost_tracked: false},",
+        "]};",
+        "const localSelected = {usage_buckets: [",
+        "  {model: 'selected', input_tokens: 100, output_tokens: 10, endpoint_cost_tracked: false},",
+        "  {model: 'paid-fallback', input_tokens: 200, output_tokens: 20, endpoint_cost_tracked: true},",
+        "]};",
+        "currentUrl = 'local';",
+        "const paidToLocal = _metricsBillableCost(paidSelected, 'final', 300, 30);",
+        "currentUrl = 'paid';",
+        "const localToPaid = _metricsBillableCost(localSelected, 'final', 300, 30);",
+        "console.log(JSON.stringify({paidToLocal, localToPaid}));",
+    ])
+
+    assert _run_node(source) == {"paidToLocal": 0.11, "localToPaid": 0.22}
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_force_answer_synthesis_segment_is_included_in_fallback_cost():
+    source = "\n".join([
+        "function _currentEndpointUrl() { return 'local-selected'; }",
+        "function isCostTrackedEndpoint() { return false; }",
+        "function getModelCost(_model, inputTokens, outputTokens) { return (inputTokens + outputTokens) / 1000; }",
+        _function_source("_billableCost"),
+        _function_source("_metricsBillableCost"),
+        "const metrics = {usage_buckets: [",
+        "  {round: 6, model: 'paid-fallback', input_tokens: 100, output_tokens: 0, endpoint_cost_tracked: true},",
+        "  {round: 6, model: 'paid-fallback', input_tokens: 80, output_tokens: 20, endpoint_cost_tracked: true},",
+        "]};",
+        "console.log(JSON.stringify({cost: _metricsBillableCost(metrics, 'paid-fallback', 180, 20)}));",
+    ])
+
+    assert _run_node(source) == {"cost": 0.2}
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_repeated_live_metrics_render_records_session_cost_once():
+    source = "\n".join([
+        "const _COST_KEY = 'ody-session-cost';",
+        "const state = {};",
+        "const localStorage = {",
+        "  getItem(key) { return state[key] || null; },",
+        "  setItem(key, value) { state[key] = value; },",
+        "};",
+        "const window = {sessionModule: {getCurrentSessionId() { return 'session'; }}};",
+        "function updateSessionCostUI() {}",
+        "function _currentEndpointUrl() { return 'local'; }",
+        "function isCostTrackedEndpoint(url) { return url === 'paid'; }",
+        "function getModelCost(_model, inputTokens, outputTokens) { return (inputTokens + outputTokens) / 1000; }",
+        _function_source("_billableCost"),
+        _function_source("_metricsBillableCost"),
+        _function_source("recordSessionMetricsCost"),
+        "const metrics = {model: 'paid-model', input_tokens: 100, output_tokens: 10, endpoint_cost_tracked: true};",
+        "recordSessionMetricsCost(metrics);",
+        "recordSessionMetricsCost(metrics);",
+        "console.log(JSON.stringify({cost: JSON.parse(state[_COST_KEY]).session, recorded: metrics._costRecorded}));",
+    ])
+
+    assert _run_node(source) == {"cost": 0.11, "recorded": True}
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_replayed_metrics_use_run_identity_for_durable_cost_deduplication():
+    source = "\n".join([
+        "const _COST_KEY = 'ody-session-cost';",
+        "const _COST_RUNS_KEY = 'ody-session-cost-runs';",
+        "const _MAX_COST_RUNS_PER_SESSION = 256;",
+        "const state = {};",
+        "const localStorage = {",
+        "  getItem(key) { return state[key] || null; },",
+        "  setItem(key, value) { state[key] = value; },",
+        "};",
+        "const window = {sessionModule: {getCurrentSessionId() { return 'session'; }}};",
+        "function updateSessionCostUI() {}",
+        "function _currentEndpointUrl() { return 'local'; }",
+        "function isCostTrackedEndpoint(url) { return url === 'paid'; }",
+        "function getModelCost(_model, inputTokens, outputTokens) { return (inputTokens + outputTokens) / 1000; }",
+        _function_source("_billableCost"),
+        _function_source("_metricsBillableCost"),
+        _function_source("recordSessionMetricsCost"),
+        _function_source("getSessionCost"),
+        "const firstObject = {model: 'paid-model', input_tokens: 100, output_tokens: 10, endpoint_cost_tracked: true, _costRecordId: 'run-1'};",
+        "const replayedObject = {...firstObject};",
+        "recordSessionMetricsCost(firstObject);",
+        "recordSessionMetricsCost(replayedObject);",
+        "console.log(JSON.stringify({cost: getSessionCost('session'), runs: JSON.parse(state[_COST_RUNS_KEY]).session}));",
+    ])
+
+    assert _run_node(source) == {"cost": 0.11, "runs": {"run-1": 0.11}}
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_run_cost_ledger_sums_segments_and_updates_repeated_segment_metrics():
+    source = "\n".join([
+        "const _COST_KEY = 'ody-session-cost';",
+        "const _COST_RUNS_KEY = 'ody-session-cost-runs';",
+        "const _MAX_COST_RUNS_PER_SESSION = 256;",
+        "const state = {};",
+        "const localStorage = {",
+        "  getItem(key) { return state[key] || null; },",
+        "  setItem(key, value) { state[key] = value; },",
+        "};",
+        "const window = {sessionModule: {getCurrentSessionId() { return 'session'; }}};",
+        "function updateSessionCostUI() {}",
+        "function _currentEndpointUrl() { return 'paid'; }",
+        "function isCostTrackedEndpoint() { return true; }",
+        "function getModelCost(_model, inputTokens, outputTokens) { return (inputTokens + outputTokens) / 1000; }",
+        _function_source("_billableCost"),
+        _function_source("_metricsBillableCost"),
+        _function_source("recordSessionMetricsCost"),
+        _function_source("getSessionCost"),
+        "recordSessionMetricsCost({model: 'student', input_tokens: 100, output_tokens: 10, _costRecordId: 'run:primary'});",
+        "recordSessionMetricsCost({model: 'student', input_tokens: 120, output_tokens: 20, _costRecordId: 'run:primary'});",
+        "recordSessionMetricsCost({model: 'teacher', input_tokens: 200, output_tokens: 30, _costRecordId: 'run:teacher'});",
+        "console.log(JSON.stringify({cost: getSessionCost('session'), runs: JSON.parse(state[_COST_RUNS_KEY]).session}));",
+    ])
+
+    assert _run_node(source) == {
+        "cost": 0.37,
+        "runs": {"run:primary": 0.14, "run:teacher": 0.23},
+    }
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_local_selected_endpoint_does_not_erase_paid_fallback_ledger():
+    source = "\n".join([
+        "const _COST_KEY = 'ody-session-cost';",
+        "const _COST_RUNS_KEY = 'ody-session-cost-runs';",
+        "const state = {'ody-session-cost': JSON.stringify({session: 0.125})};",
+        "const localStorage = {",
+        "  getItem(key) { return state[key] || null; },",
+        "  setItem(key, value) { state[key] = value; },",
+        "};",
+        "const badge = {style: {}, textContent: ''};",
+        "const document = {getElementById() { return badge; }};",
+        "const window = {sessionModule: {getCurrentSessionId() { return 'session'; }, getCurrentEndpointUrl() { return 'local'; }}};",
+        _function_source("getSessionCost"),
+        _function_source("updateSessionCostUI"),
+        "updateSessionCostUI();",
+        "console.log(JSON.stringify({stored: JSON.parse(state[_COST_KEY]).session, display: badge.style.display, text: badge.textContent}));",
+    ])
+
+    assert _run_node(source) == {
+        "stored": 0.125,
+        "display": "",
+        "text": "$0.125",
+    }
+
+
+def test_live_and_resumed_terminal_events_apply_usage_metrics_before_reload():
+    assert "metrics = json.data || metrics;" in _CHAT_SOURCE
+    assert "displayMetrics(terminalMetricsTarget, metrics);" in _CHAT_SOURCE
+    assert "metricsData = json.data || metricsData;" in _CHAT_SOURCE
+    assert "displayMetrics(holder, metricsData);" in _CHAT_SOURCE
+    assert "json.type === 'agent_terminal' || json.type === 'chat_terminal'" in _CHAT_SOURCE
+    assert "chatRenderer.recordSessionMetricsCost(metrics, streamSessionId);" in _CHAT_SOURCE
+    assert "chatRenderer.recordSessionMetricsCost(metricsData, sessionId);" in _CHAT_SOURCE
+    assert "metricsData._costRecordId = _metricsCostRecordId(resumeRunId, json);" in _CHAT_SOURCE
+    assert "bgTerminal.status = 'completed';" in _CHAT_SOURCE
+
+
+def test_usage_command_does_not_hide_existing_fallback_cost_for_local_selection():
+    assert "const cost = chatRenderer.getSessionCost" in _SLASH_SOURCE
+    assert "const cost = costTracked && chatRenderer.getSessionCost" not in _SLASH_SOURCE

tests/test_chat_model_provenance_js.py

@@ -0,0 +1,203 @@
+"""Execute the round-aware live model-provenance state helper under Node."""
+
+import json
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+
+_REPO = Path(__file__).resolve().parents[1]
+_MODULE = (_REPO / "static" / "js" / "chatModelProvenance.js").as_uri()
+
+
+def test_round_two_fallback_then_provider_alias_does_not_relabel_round_one():
+    if not shutil.which("node"):
+        pytest.skip("node is not installed")
+
+    script = f"""
+      import {{ applyModelRouteEventState }} from {json.dumps(_MODULE)};
+      const round1 = {{ _requestedModel: 'selected-model', _actualModel: 'selected-model' }};
+      const round2 = {{ _requestedModel: 'selected-model', _actualModel: 'selected-model' }};
+
+      const fallbackTarget = applyModelRouteEventState({{
+        type: 'fallback', round: 2,
+        selected_model: 'selected-model', answered_by: 'backup-model'
+      }}, round1, round2, 'selected-model');
+      const aliasTarget = applyModelRouteEventState({{
+        type: 'model_actual', round: 2,
+        requested_model: 'selected-model', model: 'provider-backup-alias'
+      }}, round1, round2, 'selected-model');
+
+      console.log(JSON.stringify({{
+        fallbackIsRound2: fallbackTarget === round2,
+        aliasIsRound2: aliasTarget === round2,
+        round1,
+        round2,
+      }}));
+    """
+    result = subprocess.run(
+        ["node", "--input-type=module"],
+        input=script,
+        capture_output=True,
+        text=True,
+        cwd=_REPO,
+        timeout=30,
+    )
+    assert result.returncode == 0, result.stderr
+    state = json.loads(result.stdout)
+    assert state == {
+        "fallbackIsRound2": True,
+        "aliasIsRound2": True,
+        "round1": {
+            "_requestedModel": "selected-model",
+            "_actualModel": "selected-model",
+        },
+        "round2": {
+            "_requestedModel": "selected-model",
+            "_actualModel": "provider-backup-alias",
+        },
+    }
+
+
+def test_next_round_and_final_metrics_preserve_each_agent_round_route():
+    if not shutil.which("node"):
+        pytest.skip("node is not installed")
+
+    script = f"""
+      import {{
+        applyModelMetricsState,
+        applyModelRouteEventState,
+        inheritModelRouteState,
+      }} from {json.dumps(_MODULE)};
+      const round1 = {{ _requestedModel: 'selected-model', _actualModel: 'selected-model' }};
+      const round2 = {{}};
+      inheritModelRouteState(round1, round1, round2, 'selected-model');
+      applyModelRouteEventState({{
+        type: 'fallback', round: 2,
+        selected_model: 'selected-model', answered_by: 'backup-model'
+      }}, round1, round2, 'selected-model');
+      applyModelRouteEventState({{
+        type: 'model_actual', round: 2,
+        requested_model: 'selected-model', model: 'provider-backup-alias'
+      }}, round1, round2, 'selected-model');
+
+      const round3 = {{}};
+      inheritModelRouteState(round1, round2, round3, 'selected-model');
+      const metricsTarget = applyModelMetricsState({{
+        requested_model: 'selected-model',
+        model: 'provider-backup-alias',
+        round_models: ['selected-model', 'provider-backup-alias', 'backup-model'],
+      }}, round1, round3, 'selected-model');
+
+      console.log(JSON.stringify({{
+        metricsIsRound3: metricsTarget === round3,
+        round1,
+        round2,
+        round3,
+      }}));
+    """
+    result = subprocess.run(
+        ["node", "--input-type=module"],
+        input=script,
+        capture_output=True,
+        text=True,
+        cwd=_REPO,
+        timeout=30,
+    )
+    assert result.returncode == 0, result.stderr
+    assert json.loads(result.stdout) == {
+        "metricsIsRound3": True,
+        "round1": {
+            "_requestedModel": "selected-model",
+            "_actualModel": "selected-model",
+        },
+        "round2": {
+            "_requestedModel": "selected-model",
+            "_actualModel": "provider-backup-alias",
+        },
+        "round3": {
+            "_requestedModel": "selected-model",
+            "_actualModel": "backup-model",
+        },
+    }
+
+
+def test_same_model_fallback_preserves_distinct_endpoint_route_state():
+    if not shutil.which("node"):
+        pytest.skip("node is not installed")
+
+    script = f"""
+      import {{ applyModelMetricsState, applyModelRouteEventState }} from {json.dumps(_MODULE)};
+      const holder = {{ _requestedModel: 'same-model', _actualModel: 'same-model' }};
+      applyModelRouteEventState({{
+        type: 'fallback',
+        selected_model: 'same-model', answered_by: 'same-model',
+        selected_endpoint_id: 'account-one', selected_endpoint_label: 'Account one',
+        answered_by_endpoint_id: 'account-two', answered_by_endpoint_label: 'Account two',
+      }}, holder, null, 'same-model');
+      applyModelMetricsState({{
+        requested_model: 'same-model', model: 'same-model',
+        requested_endpoint_id: 'account-one', requested_endpoint_label: 'Account one',
+        endpoint_id: 'account-two', endpoint_label: 'Account two',
+      }}, holder, null, 'same-model');
+      console.log(JSON.stringify(holder));
+    """
+    result = subprocess.run(
+        ["node", "--input-type=module"],
+        input=script,
+        capture_output=True,
+        text=True,
+        cwd=_REPO,
+        timeout=30,
+    )
+    assert result.returncode == 0, result.stderr
+    assert json.loads(result.stdout) == {
+        "_requestedModel": "same-model",
+        "_actualModel": "same-model",
+        "_requestedEndpointId": "account-one",
+        "_requestedEndpointLabel": "Account one",
+        "_actualEndpointId": "account-two",
+        "_actualEndpointLabel": "Account two",
+    }
+
+
+def test_metrics_preserve_explicitly_unknown_round_endpoint():
+    if not shutil.which("node"):
+        pytest.skip("node is not installed")
+
+    script = f"""
+      import {{ applyModelMetricsState }} from {json.dumps(_MODULE)};
+      const holder = {{
+        _requestedModel: 'same-model',
+        _actualModel: 'same-model',
+        _requestedEndpointId: 'account-one',
+        _requestedEndpointLabel: 'Account one',
+      }};
+      const roundHolder = {{}};
+      applyModelMetricsState({{
+        requested_model: 'same-model', model: 'same-model',
+        requested_endpoint_id: 'account-one', requested_endpoint_label: 'Account one',
+        endpoint_id: 'account-two', endpoint_label: 'Account two',
+        round_endpoint_ids: [null], round_endpoint_labels: [null],
+      }}, holder, roundHolder, 'same-model');
+      console.log(JSON.stringify(roundHolder));
+    """
+    result = subprocess.run(
+        ["node", "--input-type=module"],
+        input=script,
+        capture_output=True,
+        text=True,
+        cwd=_REPO,
+        timeout=30,
+    )
+    assert result.returncode == 0, result.stderr
+    assert json.loads(result.stdout) == {
+        "_requestedModel": "same-model",
+        "_actualModel": "same-model",
+        "_requestedEndpointId": "account-one",
+        "_requestedEndpointLabel": "Account one",
+        "_actualEndpointId": None,
+        "_actualEndpointLabel": None,
+    }

tests/test_chat_stream_errors_js.py

@@ -0,0 +1,47 @@
+"""Execute terminal stream-error classification under Node."""
+
+import json
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+
+_REPO = Path(__file__).resolve().parents[1]
+_MODULE = (_REPO / "static" / "js" / "chatStreamErrors.js").as_uri()
+
+
+def test_terminal_provider_errors_preserve_text_and_never_auto_retry():
+    if not shutil.which("node"):
+        pytest.skip("node is not installed")
+
+    script = f"""
+      import {{ createTerminalStreamError, isRecoverableStreamError }} from {json.dumps(_MODULE)};
+      const stringError = createTerminalStreamError({{ status: 401, error: 'invalid key' }});
+      const objectError = createTerminalStreamError({{ status: 404, error: {{ message: 'model missing' }} }});
+      console.log(JSON.stringify({{
+        stringMessage: stringError.message,
+        objectMessage: objectError.message,
+        terminalRecoverable: isRecoverableStreamError(stringError),
+        eofRecoverable: isRecoverableStreamError(new Error('Stream closed before completion')),
+        networkRecoverable: isRecoverableStreamError(new TypeError('fetch failed')),
+      }}));
+    """
+    result = subprocess.run(
+        ["node", "--input-type=module"],
+        input=script,
+        capture_output=True,
+        text=True,
+        cwd=_REPO,
+        timeout=30,
+    )
+
+    assert result.returncode == 0, result.stderr
+    assert json.loads(result.stdout) == {
+        "stringMessage": "invalid key",
+        "objectMessage": "model missing",
+        "terminalRecoverable": False,
+        "eofRecoverable": True,
+        "networkRecoverable": True,
+    }

tests/test_compare_stop_disconnect_poll.py

@@ -81,6 +81,13 @@ def _make_stream_with_save(sink, chunks, *, hang_after=None):
     return gen()
 
 
+async def _collect_subscription(session_id, expected_run=None):
+    return [
+        event
+        async for event in agent_runs.subscribe(session_id, expected_run)
+    ]
+
+
 # --------------------------------------------------------------------------- #
 # agent_runs: detached-run semantics (what NORMAL chat/agent streams use)
 # --------------------------------------------------------------------------- #
@@ -136,7 +143,7 @@ async def test_stop_cancels_detached_run_and_saves_partial_exactly_once():
             break
     await sub.aclose()
 
-    stopped = agent_runs.stop(session_id)
+    stopped = agent_runs.stop(session_id, run.run_id)
     assert stopped is True
 
     await run.task  # propagates promptly — not stuck on the hung await
@@ -165,6 +172,172 @@ async def test_normal_completion_saves_exactly_once_not_partial():
     assert sink.saves == []
 
 
+@pytest.mark.asyncio
+async def test_detached_run_identity_is_stable_for_replay_and_unique_per_run():
+    session_id = "sess-detached-run-identity"
+    agent_runs._RUNS.pop(session_id, None)
+
+    first = agent_runs.start(session_id, _make_stream_with_save(_FakeSaveSink(), ["one"]))
+    first_id = first.run_id
+    assert agent_runs.get_run_id(session_id) == first_id
+    await first.task
+    assert agent_runs.get_run_id(session_id) == first_id
+
+    second = agent_runs.start(session_id, _make_stream_with_save(_FakeSaveSink(), ["two"]))
+    assert second.run_id != first_id
+    assert agent_runs.get_run_id(session_id) == second.run_id
+    await second.task
+
+
+@pytest.mark.asyncio
+async def test_lazy_subscription_stays_bound_to_header_run_after_replacement():
+    session_id = "sess-detached-lazy-subscription"
+    agent_runs._RUNS.pop(session_id, None)
+
+    async def stream(label):
+        yield f'data: {{"delta":"{label}"}}\n\n'
+
+    first = agent_runs.start(session_id, stream("first"))
+    await first.task
+    # StreamingResponse does not iterate its body until after construction.
+    # Capture the same exact run object used for its identity header.
+    lazy_body = agent_runs.subscribe(session_id, first)
+
+    second = agent_runs.start(session_id, stream("second"))
+    await second.task
+
+    replayed = [event async for event in lazy_body]
+    assert replayed == ['data: {"delta":"first"}\n\n']
+    assert agent_runs.get_run_id(session_id) == second.run_id
+
+
+@pytest.mark.asyncio
+async def test_stale_run_identity_cannot_stop_replacement_run():
+    session_id = "sess-detached-stale-stop"
+    agent_runs._RUNS.pop(session_id, None)
+    release = asyncio.Event()
+
+    async def finished():
+        yield 'data: {"delta":"old"}\n\n'
+
+    async def replacement():
+        yield 'data: {"delta":"new"}\n\n'
+        await release.wait()
+
+    first = agent_runs.start(session_id, finished())
+    await first.task
+    second = agent_runs.start(session_id, replacement())
+    await asyncio.sleep(0)
+
+    assert agent_runs.stop(session_id) is False
+    assert agent_runs.stop(session_id, first.run_id) is False
+    assert second.task is not None and not second.task.done()
+    assert agent_runs.stop(session_id, second.run_id) is True
+    await second.task
+
+
+@pytest.mark.asyncio
+async def test_triple_replacement_closes_middle_subscriber_and_preserves_save_order():
+    session_id = "sess-detached-triple-replacement"
+    agent_runs._RUNS.pop(session_id, None)
+    first_closing = asyncio.Event()
+    release_first = asyncio.Event()
+    third_started = asyncio.Event()
+
+    async def first_stream():
+        try:
+            yield 'data: {"delta":"first"}\n\n'
+            await asyncio.Event().wait()
+        finally:
+            first_closing.set()
+            await release_first.wait()
+
+    async def middle_stream():
+        yield 'data: {"delta":"middle"}\n\n'
+
+    async def third_stream():
+        third_started.set()
+        yield 'data: {"delta":"third"}\n\n'
+
+    first = agent_runs.start(session_id, first_stream())
+    while not first.buffer:
+        await asyncio.sleep(0)
+
+    middle = agent_runs.start(session_id, middle_stream())
+    await first_closing.wait()
+    assert middle.task is not None and not middle.task.done()
+
+    middle_events_task = asyncio.create_task(
+        _collect_subscription(session_id, middle)
+    )
+    while not middle.subscribers:
+        await asyncio.sleep(0)
+
+    third = agent_runs.start(session_id, third_stream())
+
+    # The superseded middle response closes immediately even though its task
+    # remains as the transitive barrier for the first run's partial save.
+    assert await asyncio.wait_for(middle_events_task, timeout=1) == []
+    assert middle.status == "stopped"
+    assert middle.task is not None and not middle.task.done()
+    assert not third_started.is_set()
+
+    release_first.set()
+    await asyncio.wait_for(first.task, timeout=1)
+    await asyncio.wait_for(middle.task, timeout=1)
+    await asyncio.wait_for(third.task, timeout=1)
+
+    assert first.status == "stopped"
+    assert middle.status == "stopped"
+    assert third.status == "done"
+    assert third_started.is_set()
+
+
+@pytest.mark.asyncio
+async def test_reconnect_replays_pinned_fallback_run_without_restarting_tools():
+    session_id = "sess-detached-fallback-resume"
+    agent_runs._RUNS.pop(session_id, None)
+    release = asyncio.Event()
+    tool_executions = 0
+    fallback = 'data: {"type":"fallback","answered_by":"backup","candidate_index":1}\n\n'
+    tool = 'data: {"type":"tool_output","tool":"bash","output":"ok"}\n\n'
+
+    async def pinned_run():
+        nonlocal tool_executions
+        yield fallback
+        tool_executions += 1
+        yield tool
+        await release.wait()
+        yield 'data: {"delta":"backup finished"}\n\n'
+        yield "data: [DONE]\n\n"
+
+    run = agent_runs.start(session_id, pinned_run())
+    first = agent_runs.subscribe(session_id)
+    first_events = []
+    async for event in first:
+        first_events.append(event)
+        if len(first_events) == 2:
+            break
+    await first.aclose()
+
+    assert run.status == "running"
+    assert tool_executions == 1
+    assert agent_runs._RUNS[session_id] is run
+
+    resumed_events = []
+    resumed = agent_runs.subscribe(session_id)
+    async for event in resumed:
+        resumed_events.append(event)
+        if len(resumed_events) == 2:
+            release.set()
+    await run.task
+
+    assert resumed_events[:2] == [fallback, tool]
+    assert resumed_events[-1] == "data: [DONE]\n\n"
+    assert tool_executions == 1
+    assert agent_runs._RUNS[session_id] is run
+
+
 # --------------------------------------------------------------------------- #
 # chat_stream: Compare panes must NOT be detached, so the Stop button (closing
 # the SSE) cancels the upstream generator promptly — exercising the same

tests/test_context_compactor.py

@@ -63,6 +63,23 @@ class TestSelfSummaryPrompt:
 
 
 class TestTrimForContext:
+    def test_system_truncation_preserves_internal_route_metadata(self):
+        messages = [
+            {
+                "role": "system",
+                "content": "persona\n\n" + ("agent prompt " * 2000),
+                "_agent_injected": "merged_prompt",
+                "_agent_base_message": {"role": "system", "content": "persona"},
+            },
+            {"role": "user", "content": "latest"},
+        ]
+
+        trimmed = trim_for_context(messages, context_length=1024, reserve_tokens=256)
+
+        system = next(message for message in trimmed if message.get("role") == "system")
+        assert system["_agent_injected"] == "merged_prompt"
+        assert system["_agent_base_message"] == {"role": "system", "content": "persona"}
+
     def test_keeps_current_large_user_message_by_truncating(self):
         huge = "A" * 20000
         messages = [
@@ -194,6 +211,50 @@ class TestMaybeCompactFourthMessage:
         assert len(result) == 3 and result[2] is True
 
 
+@pytest.mark.asyncio
+async def test_deferred_compaction_persists_only_after_route_commit(monkeypatch):
+    updates = []
+    state = {}
+    messages = [
+        {"role": "system", "content": "system " * 100},
+        {"role": "user", "content": "one"},
+        {"role": "assistant", "content": "two"},
+        {"role": "user", "content": "three"},
+        {"role": "assistant", "content": "four"},
+        {"role": "user", "content": "five"},
+    ]
+
+    monkeypatch.setattr(cc, "get_context_length", lambda *args: 100)
+    monkeypatch.setattr(cc, "resolve_endpoint", lambda *args, **kwargs: (None, None, None))
+
+    async def fake_summary(*args, **kwargs):
+        return "route-specific summary"
+
+    monkeypatch.setattr(cc, "llm_call_async", fake_summary)
+    monkeypatch.setattr(
+        cc,
+        "_update_session_history",
+        lambda *args, **kwargs: updates.append((args, kwargs)),
+    )
+
+    _compacted, _context, was_compacted = await cc.maybe_compact(
+        object(),
+        "https://candidate.example/v1",
+        "candidate-model",
+        messages,
+        persist=False,
+        compaction_state=state,
+    )
+
+    assert was_compacted is True
+    assert updates == []
+    assert state["summary"] == "route-specific summary"
+    assert cc.apply_compaction_state(object(), state) is True
+    assert len(updates) == 1
+    assert cc.apply_compaction_state(object(), state) is False
+    assert len(updates) == 1
+
+
 class TestResearchPrimerPreserved:
     """A research-spinoff primer (metadata research_spinoff_from) must never be
     trimmed away — it is the Discuss chat's sole knowledge base (drift fix)."""

tests/test_legacy_default_fallback_ui.py

@@ -8,15 +8,15 @@ from bs4 import BeautifulSoup
 _REPO = Path(__file__).resolve().parents[1]
 
 
-def test_legacy_default_fallback_editor_is_hidden():
+def test_legacy_default_fallback_editor_is_absent():
     soup = BeautifulSoup(
         (_REPO / "static" / "index.html").read_text(encoding="utf-8"),
         "html.parser",
     )
     editor = soup.find(id="set-defaultFallbacks")
 
-    assert editor is not None
+    assert editor is None
-    assert editor.find_parent(class_="settings-row").has_attr("hidden")
+    assert soup.find(id="set-defaultAddFallback") is None
 
 
 def test_default_model_save_does_not_rewrite_legacy_fallbacks():
@@ -27,3 +27,5 @@ def test_default_model_save_does_not_rewrite_legacy_fallbacks():
 
     assert "settings.default_model_fallbacks" not in default_chat_source
     assert "default_model_fallbacks:" not in default_chat_source
+    assert "set-defaultFallbacks" not in default_chat_source
+    assert "set-defaultAddFallback" not in default_chat_source

tests/test_live_fallback_round_attribution.py

@@ -0,0 +1,284 @@
+"""Source contract for live multi-round fallback attribution."""
+
+import json
+from pathlib import Path
+import shutil
+import subprocess
+
+import pytest
+
+
+CHAT_JS = Path("static/js/chat.js").read_text(encoding="utf-8")
+_HAS_NODE = shutil.which("node") is not None
+
+
+def _resume_function_source():
+    body = CHAT_JS.split("export async function resumeStream", 1)[1].split(
+        "export function checkBackgroundStream", 1
+    )[0]
+    return "async function resumeStream" + body.rstrip()
+
+
+def _run_node(source):
+    proc = subprocess.run(
+        ["node", "--input-type=module"],
+        input=source,
+        capture_output=True,
+        text=True,
+        timeout=30,
+    )
+    assert proc.returncode == 0, proc.stderr
+    return json.loads(proc.stdout.strip())
+
+
+def test_live_fallback_targets_the_active_round_and_replaces_actual_model():
+    fallback_block = CHAT_JS.split("json.type === 'fallback'", 1)[1].split(
+        "json.type === 'doc_stream_open'", 1
+    )[0]
+
+    assert "applyModelRouteEventState(json, holder, roundHolder, modelName)" in fallback_block
+    assert "_fallbackHolder.querySelector('.role')" in fallback_block
+    assert "_hasResolvedActual" not in fallback_block
+
+
+def test_provider_alias_uses_the_same_round_aware_holder_selection():
+    actual_block = CHAT_JS.split("json.type === 'model_actual'", 1)[1].split(
+        "json.type === 'attachments'", 1
+    )[0]
+
+    assert "applyModelRouteEventState(json, holder, roundHolder, modelName)" in actual_block
+    assert "_modelHolder.querySelector('.role')" in actual_block
+
+
+def test_new_round_and_final_metrics_target_the_active_round():
+    agent_step_block = CHAT_JS.split("} else if (json.type === 'agent_step')", 1)[1].split(
+        "json.type === 'budget_exceeded'", 1
+    )[0]
+    metrics_block = CHAT_JS.split("json.type === 'metrics'", 1)[1].split(
+        "json.type === 'message_saved'", 1
+    )[0]
+    final_block = CHAT_JS.split("const _isBgFinal", 1)[1].split(
+        "holder.dataset.raw", 1
+    )[0]
+
+    assert "inheritModelRouteState(holder, roundHolder, newWrap" in agent_step_block
+    assert "applyModelMetricsState(metrics, holder, roundHolder, modelName)" in metrics_block
+    assert "_finalModelHolder.querySelector('.role')" in final_block
+    assert "holder.querySelector('.role')" not in final_block
+
+
+def test_terminal_sse_error_bypasses_eof_auto_recovery():
+    parser_block = CHAT_JS.split("if (_nextIsError || json.status >= 400)", 1)[1].split(
+        "if (json.delta", 1
+    )[0]
+    completion_gate = CHAT_JS.split("if (_streamTerminalError)", 1)[1].split(
+        "if (!_streamSawDone)", 1
+    )[0]
+    recovery_block = CHAT_JS.split("isRecoverableStreamError(err)", 1)[1].split(
+        "const errorHolder", 1
+    )[0]
+
+    assert "createTerminalStreamError(json)" in parser_block
+    assert "throw _streamTerminalError" in completion_gate
+    assert "if (err.terminalStreamError)" in recovery_block
+    assert "await sessionModule.selectSession(streamSessionId, { showLoading: false })" in recovery_block
+
+
+def test_connection_recovery_resumes_detached_run_without_resubmitting_selected_model():
+    recovery = CHAT_JS.split("function _tryAutoRecover", 1)[1].split(
+        "function _removeStallBanner", 1
+    )[0]
+
+    assert "await resumeStream(sessionId, holder || null)" in recovery
+    assert "/api/chat_stream" not in recovery
+    assert ".click()" not in recovery
+    assert "_pendingContinue" not in recovery
+    assert "if (_streamSessionId === streamSessionId) _streamSessionId = null" in CHAT_JS
+
+
+def test_detached_resume_reloads_canonical_terminal_failures():
+    resume = CHAT_JS.split("export async function resumeStream", 1)[1].split(
+        "export function checkBackgroundStream", 1
+    )[0]
+
+    assert "l.trim() === 'event: error'" in resume
+    assert "json.type === 'agent_terminal'" in resume
+    assert "rich = true" in resume
+    assert "Network drop or parse failure: fall through to the canonical reload" in resume
+    assert "if (onThisSession && !rich && roundText.trim())" in resume
+    assert "res.headers.get('X-Odysseus-Run-Id')" in resume
+    assert "chatRenderer.recordSessionMetricsCost(metricsData, sessionId)" in resume
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_detached_resume_surfaces_fallback_then_provider_alias_before_reload():
+    source = "\n".join([
+        "import { applyModelRouteEventState } from './static/js/chatModelProvenance.js';",
+        "class Element {",
+        "  constructor(tag = 'div') { this.tag = tag; this.children = []; this.parentNode = null; this.style = {}; this.textContent = ''; this._html = ''; }",
+        "  appendChild(child) { child.parentNode = this; this.children.push(child); return child; }",
+        "  remove() { if (!this.parentNode) return; this.parentNode.children = this.parentNode.children.filter(c => c !== this); this.parentNode = null; }",
+        "  set innerHTML(value) {",
+        "    this._html = value;",
+        "    if (value.includes('stream-content')) {",
+        "      this._role = new Element('div'); this._role.parentNode = this;",
+        "      this._body = new Element('div'); this._body.parentNode = this;",
+        "      this._content = new Element('div'); this._body.appendChild(this._content);",
+        "    }",
+        "  }",
+        "  get innerHTML() { return this._html; }",
+        "  querySelector(selector) { if (selector === '.role') return this._role || null; if (selector === '.body') return this._body || null; if (selector === '.stream-content') return this._content || null; return null; }",
+        "}",
+        "const box = new Element('main');",
+        "const document = { getElementById(id) { return id === 'chat-history' ? box : null; }, createElement(tag) { return new Element(tag); } };",
+        "const window = {};",
+        "let selectCalls = 0; const labels = []; const toasts = [];",
+        "const sessionModule = { getSessions() { return [{id: 's1', model: 'selected-model'}]; }, getCurrentSessionId() { return 's1'; }, selectSession() { selectCalls += 1; }, loadSessions() {} };",
+        "const uiModule = { esc(value) { return String(value); }, scrollHistory() {}, showToast(value) { toasts.push(value); } };",
+        "const spinnerModule = { create() { return { element: null, createElement() { this.element = new Element('spinner'); return this.element; }, start() {}, destroy() { if (this.element) this.element.remove(); } }; } };",
+        "const markdownModule = { normalizeThinkingMarkup(v) { return v; }, mdToHtml(v) { return v; }, squashOutsideCode(v) { return v; } };",
+        "const documentModule = null; const chatRenderer = { recordSessionMetricsCost() {}, addMessage() {} };",
+        "const _resumingStreams = new Set(); const _streamRunIds = new Map(); const API_BASE = '';",
+        "function hasActiveStream() { return false; } function _shortModel(v) { return v; } function _applyModelColor() {}",
+        "function _setRoleModelLabel(role, requested, actual) { labels.push({requested, actual}); role.textContent = requested + ' -> ' + actual; }",
+        "function _streamDisplayText(v) { return v; } function _showDocumentWritingStatus() {} function _finishDocumentWritingStatus() {} function _metricsCostRecordId() { return 'run'; }",
+        "const events = [",
+        "  'data: {\"type\":\"fallback\",\"selected_model\":\"selected-model\",\"answered_by\":\"fallback-model\",\"reason\":\"429\"}\\n\\n',",
+        "  'data: {\"type\":\"model_actual\",\"model\":\"provider/fallback-alias\"}\\n\\n',",
+        "  'data: {\"delta\":\"hello\"}\\n\\n',",
+        "  'data: [DONE]\\n\\n',",
+        "].join('');",
+        "const encoded = new TextEncoder().encode(events); let reads = 0;",
+        "const reader = { async read() { return reads++ === 0 ? {done:false, value:encoded} : {done:true}; }, async cancel() {} };",
+        "async function fetch() { return { ok:true, body:{getReader(){return reader;}}, headers:{get(){return 'run-1';}} }; }",
+        _resume_function_source(),
+        "await resumeStream('s1');",
+        "console.log(JSON.stringify({labels, toasts, selectCalls, holderCount: box.children.length}));",
+    ])
+
+    assert _run_node(source) == {
+        "labels": [
+            {"requested": "selected-model", "actual": "fallback-model"},
+            {"requested": "selected-model", "actual": "provider/fallback-alias"},
+        ],
+        "toasts": ["Fallback: selected-model failed — answered by fallback-model"],
+        "selectCalls": 1,
+        "holderCount": 0,
+    }
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_detached_resume_renders_preoutput_error_without_empty_reload():
+    source = "\n".join([
+        "import { createTerminalStreamError } from './static/js/chatStreamErrors.js';",
+        "class Element {",
+        "  constructor(tag = 'div') { this.tag = tag; this.children = []; this.parentNode = null; this.style = {}; this.textContent = ''; this._html = ''; }",
+        "  appendChild(child) { child.parentNode = this; this.children.push(child); return child; }",
+        "  remove() { if (!this.parentNode) return; this.parentNode.children = this.parentNode.children.filter(c => c !== this); this.parentNode = null; }",
+        "  set innerHTML(value) {",
+        "    this._html = value;",
+        "    if (value.includes('stream-content')) {",
+        "      this._role = new Element('div'); this._role.parentNode = this;",
+        "      this._body = new Element('div'); this._body.parentNode = this;",
+        "      this._content = new Element('div'); this._body.appendChild(this._content);",
+        "    }",
+        "  }",
+        "  get innerHTML() { return this._html; }",
+        "  querySelector(selector) { if (selector === '.role') return this._role || null; if (selector === '.body') return this._body || null; if (selector === '.stream-content') return this._content || null; return null; }",
+        "}",
+        "const box = new Element('main');",
+        "const document = { getElementById(id) { return id === 'chat-history' ? box : null; }, createElement(tag) { return new Element(tag); } };",
+        "const window = {};",
+        "let selectCalls = 0;",
+        "const sessionModule = { getSessions() { return [{id: 's1', model: 'selected'}]; }, getCurrentSessionId() { return 's1'; }, selectSession() { selectCalls += 1; }, loadSessions() {} };",
+        "const uiModule = { esc(value) { return String(value); }, scrollHistory() {} };",
+        "const spinnerModule = { create() { return { element: null, createElement() { this.element = new Element('spinner'); return this.element; }, start() {}, destroy() { if (this.element) this.element.remove(); } }; } };",
+        "const markdownModule = { normalizeThinkingMarkup(v) { return v; }, mdToHtml(v) { return v; }, squashOutsideCode(v) { return v; } };",
+        "const documentModule = null;",
+        "const chatRenderer = { recordSessionMetricsCost() {}, addMessage() {} };",
+        "const _resumingStreams = new Set(); const _streamRunIds = new Map(); const API_BASE = '';",
+        "function hasActiveStream() { return false; } function _shortModel(v) { return v; } function _applyModelColor() {}",
+        "function _streamDisplayText(v) { return v; } function _showDocumentWritingStatus() {} function _finishDocumentWritingStatus() {} function _metricsCostRecordId() { return 'run'; }",
+        "const encoded = new TextEncoder().encode('event: error\\ndata: {\"status\":401,\"error\":\"invalid key <img src=x>\"}\\n\\n');",
+        "let reads = 0; const reader = { async read() { return reads++ === 0 ? {done:false, value:encoded} : {done:true}; }, async cancel() {} };",
+        "async function fetch() { return { ok:true, body:{getReader(){return reader;}}, headers:{get(){return 'run-1';}} }; }",
+        _resume_function_source(),
+        "const result = await resumeStream('s1');",
+        "const holder = box.children[0]; const errorNode = holder && holder._content.children.find(node => node.textContent.startsWith('[Error:'));",
+        "console.log(JSON.stringify({result, selectCalls, holderCount: box.children.length, errorText: errorNode && errorNode.textContent}));",
+    ])
+
+    assert _run_node(source) == {
+        "result": True,
+        "selectCalls": 0,
+        "holderCount": 1,
+        "errorText": "[Error: invalid key <img src=x>]",
+    }
+
+
+def test_terminal_then_session_switch_preserves_completed_background_state():
+    terminal = CHAT_JS.split(
+        "json.type === 'agent_terminal' || json.type === 'chat_terminal'", 1
+    )[1].split("json.type === 'metrics'", 1)[0]
+    detach = CHAT_JS.split("export function detachCurrentStream", 1)[1].split(
+        "export async function resumeStream", 1
+    )[0]
+    background_catch = CHAT_JS.split("if (_isBgCatch)", 1)[1].split(
+        "} else {", 1
+    )[0]
+
+    assert "_terminalSavedStreams.add(streamSessionId)" in terminal
+    assert "terminalSaved ? 'completed' : 'running'" in detach
+    assert "!terminalSaved && sessionModule && sessionModule.markStreaming" in detach
+    assert "_terminalSavedStreams.has(streamSessionId)" in background_catch
+
+
+def test_detached_run_identity_is_attached_to_live_metrics():
+    routes = Path("routes/chat_routes.py").read_text(encoding="utf-8")
+    assert "headers={\"X-Odysseus-Run-Id\": _detached_run.run_id}" in routes
+    assert "agent_runs.subscribe(session, _detached_run)" in routes
+    assert "agent_runs.subscribe(session_id, _active_run)" in routes
+    assert "const streamRunId = res.headers.get('X-Odysseus-Run-Id')" in CHAT_JS
+    assert "metrics._costRecordId = _metricsCostRecordId(streamRunId, json)" in CHAT_JS
+    assert "'X-Odysseus-Run-Id': runId" in CHAT_JS
+    assert "agent_runs.stop(session_id, _expected_run_id)" in routes
+    assert "_stopExactRun(streamSessionId)" in CHAT_JS
+    timeout_block = CHAT_JS.split("timeoutId = setTimeout", 1)[1].split(
+        "clearResponseTimeout", 1
+    )[0]
+    assert "/api/chat/stop/" not in timeout_block
+
+
+def test_replay_cost_identity_distinguishes_primary_and_teacher_segments():
+    identity = CHAT_JS.split("function _metricsCostRecordId", 1)[1].split("\n  }", 1)[0]
+    resume = CHAT_JS.split("export async function resumeStream", 1)[1].split(
+        "export function checkBackgroundStream", 1
+    )[0]
+
+    assert "event.teacher ? 'teacher' : 'primary'" in identity
+    assert "_metricsCostRecordId(resumeRunId, json)" in resume
+    metrics_block = resume.split("json.type === 'metrics'", 1)[1].split(
+        "json.type === 'agent_terminal'", 1
+    )[0]
+    assert "chatRenderer.recordSessionMetricsCost(metricsData, sessionId)" in metrics_block
+
+    routes = Path("routes/chat_routes.py").read_text(encoding="utf-8")
+    route_metrics = routes.split('elif data.get("type") == "metrics"', 1)[1].split(
+        "except json.JSONDecodeError", 1
+    )[0]
+    assert 'if data.get("teacher") is True' in route_metrics
+    assert '_metrics_event["teacher"] = True' in route_metrics
+
+
+def test_foreground_terminal_error_reloads_saved_partial_without_typewriter_race():
+    parser = CHAT_JS.split("if (_nextIsError || json.status >= 400)", 1)[1].split(
+        "if (json.delta", 1
+    )[0]
+    terminal_catch = CHAT_JS.split("if (err.terminalStreamError)", 1)[1].split(
+        "const errorHolder", 1
+    )[0]
+
+    assert "typewriterInto" not in parser
+    assert "json.type === 'agent_terminal'" in CHAT_JS
+    assert "_canonicalTerminalSaved = true" in CHAT_JS
+    assert "await sessionModule.selectSession(streamSessionId, { showLoading: false })" in terminal_catch

tests/test_llm_core_usage_finish_delta.py

@@ -9,6 +9,8 @@ stream_llm only captured usage when the delta was exactly None / {} /
 import asyncio
 import json
 
+import pytest
+
 from src import llm_core
 
 
@@ -116,7 +118,8 @@ def test_null_choice_chunk_does_not_crash(monkeypatch):
 
 
 def test_null_choice_with_null_usage_does_not_crash(monkeypatch):
-    # Chunk with both choices:[null] and usage:null — neither field should panic.
+    # Chunk with both choices:[null] and usage:null is a keepalive, not a real
+    # zero-token accounting record.
     lines = [
         'data: ' + json.dumps({"choices": [{"delta": {"content": "Hi"}}]}),
         'data: ' + json.dumps({"choices": [None], "usage": None}),
@@ -124,6 +127,66 @@ def test_null_choice_with_null_usage_does_not_crash(monkeypatch):
     ]
     result = _drive(monkeypatch, lines)
     assert "Hi" in result
+    assert _usage_events(result) == []
+
+
+def test_empty_usage_object_is_not_reported_as_real_zero_usage(monkeypatch):
+    lines = [
+        'data: ' + json.dumps({"choices": [{"delta": {"content": "Hi"}}]}),
+        'data: ' + json.dumps({"choices": [], "usage": {}}),
+        'data: [DONE]',
+    ]
+    result = _drive(monkeypatch, lines)
+    assert "Hi" in result
+    assert _usage_events(result) == []
+
+
+def test_explicit_zero_token_usage_is_preserved(monkeypatch):
+    lines = [
+        'data: ' + json.dumps({"choices": [{"delta": {"content": "Hi"}}]}),
+        'data: ' + json.dumps({
+            "choices": [],
+            "usage": {"prompt_tokens": 0, "completion_tokens": 0},
+        }),
+        'data: [DONE]',
+    ]
+    usage = _usage_events(_drive(monkeypatch, lines))
+    assert usage == [{"input_tokens": 0, "output_tokens": 0}]
+
+
+@pytest.mark.parametrize(
+    "usage_payload",
+    [
+        {"prompt_tokens": None, "completion_tokens": 1},
+        {"prompt_tokens": "bad", "completion_tokens": 1},
+        {"prompt_tokens": -1, "completion_tokens": 1},
+        {"prompt_tokens": True, "completion_tokens": 1},
+        {"prompt_tokens": 1.5, "completion_tokens": 1},
+        {"prompt_tokens": float("inf"), "completion_tokens": 1},
+    ],
+)
+def test_malformed_token_values_do_not_emit_usage(monkeypatch, usage_payload):
+    lines = [
+        'data: ' + json.dumps({"choices": [{"delta": {"content": "Hi"}}]}),
+        'data: ' + json.dumps({"choices": [], "usage": usage_payload}),
+        'data: [DONE]',
+    ]
+    result = _drive(monkeypatch, lines)
+    assert "Hi" in result
+    assert _usage_events(result) == []
+
+
+def test_missing_usage_counterpart_defaults_to_zero(monkeypatch):
+    lines = [
+        'data: ' + json.dumps({"choices": [{"delta": {"content": "Hi"}}]}),
+        'data: ' + json.dumps({
+            "choices": [],
+            "usage": {"completion_tokens": 2},
+        }),
+        'data: [DONE]',
+    ]
+    usage = _usage_events(_drive(monkeypatch, lines))
+    assert usage == [{"input_tokens": 0, "output_tokens": 2}]
 
 
 def test_null_tool_call_in_delta_is_skipped(monkeypatch):

tests/test_model_routes.py

@@ -98,6 +98,9 @@ def test_endpoint_cleanup_preserves_legacy_default_fallback_data():
             {"endpoint_id": "dead", "model": "fallback-a"},
             {"endpoint_id": "keep", "model": "fallback-b"},
         ],
+        "foreground_model_fallbacks": [
+            {"endpoint_id": "dead", "model": "foreground"},
+        ],
         "utility_model_fallbacks": [{"endpoint_id": "dead", "model": "utility"}],
         "vision_model_fallbacks": [{"endpoint_id": "dead", "model": "vision"}],
         "stt_provider": "endpoint:dead",
@@ -106,12 +109,14 @@ def test_endpoint_cleanup_preserves_legacy_default_fallback_data():
 
     assert _endpoint_settings_using_endpoint(settings, "dead", include_speech=True) == [
         "Default Model",
+        "Foreground Model Fallbacks",
         "Utility Model Fallbacks",
         "Vision Model Fallbacks",
         "Speech to Text",
     ]
     assert _clear_endpoint_settings_for_endpoint(settings, "dead", include_speech=True) == [
         "Default Model",
+        "Foreground Model Fallbacks",
         "Utility Model Fallbacks",
         "Vision Model Fallbacks",
         "Speech to Text",
@@ -122,6 +127,7 @@ def test_endpoint_cleanup_preserves_legacy_default_fallback_data():
         {"endpoint_id": "dead", "model": "fallback-a"},
         {"endpoint_id": "keep", "model": "fallback-b"},
     ]
+    assert settings["foreground_model_fallbacks"] == []
     assert settings["utility_model_fallbacks"] == []
     assert settings["vision_model_fallbacks"] == []
     assert settings["stt_provider"] == "disabled"
@@ -130,10 +136,19 @@ def test_endpoint_cleanup_preserves_legacy_default_fallback_data():
 
 def test_endpoint_cleanup_updates_active_scoped_prefs_but_preserves_legacy_data():
     scoped = {
+        "foreground_model_fallbacks": [
+            {"endpoint_id": "dead", "model": "ownerless"},
+        ],
+        "default_model_fallbacks": [
+            {"endpoint_id": "dead", "model": "legacy-ownerless"},
+        ],
         "_users": {
             "alice": {
                 "utility_endpoint_id": "dead",
                 "utility_model": "utility",
+                "foreground_model_fallbacks": [
+                    {"endpoint_id": "dead", "model": "foreground"},
+                ],
                 "vision_model_fallbacks": [{"endpoint_id": "dead", "model": "vision"}],
             },
             "bob": {
@@ -142,10 +157,15 @@ def test_endpoint_cleanup_updates_active_scoped_prefs_but_preserves_legacy_data(
             },
         },
     }
-    assert _clear_user_pref_endpoint_refs(scoped, "dead") == 1
+    assert _clear_user_pref_endpoint_refs(scoped, "dead") == 2
+    assert scoped["foreground_model_fallbacks"] == []
+    assert scoped["default_model_fallbacks"] == [
+        {"endpoint_id": "dead", "model": "legacy-ownerless"},
+    ]
     assert scoped["_users"]["alice"] == {
         "utility_endpoint_id": "",
         "utility_model": "",
+        "foreground_model_fallbacks": [],
         "vision_model_fallbacks": [],
     }
     assert scoped["_users"]["bob"]["default_endpoint_id"] == "keep"

tests/test_pr6020_browser_review_regressions.py

@@ -0,0 +1,933 @@
+"""Executable regressions for the browser/run-lifecycle review of PR #6020.
+
+These tests intentionally exercise JavaScript under Node rather than treating
+``node --check`` or source-string presence as proof that the browser paths are
+usable.  The detached-run replacement case drives the real Python manager.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import json
+from pathlib import Path
+import re
+import shutil
+import subprocess
+
+import pytest
+
+from src import agent_runs
+
+
+_REPO = Path(__file__).resolve().parents[1]
+_CHAT_PATH = _REPO / "static" / "js" / "chat.js"
+_CHAT = _CHAT_PATH.read_text(encoding="utf-8")
+_RENDERER = (_REPO / "static" / "js" / "chatRenderer.js").read_text(
+    encoding="utf-8"
+)
+_STREAM_ERRORS_URI = (_REPO / "static" / "js" / "chatStreamErrors.js").as_uri()
+_HAS_NODE = shutil.which("node") is not None
+
+
+def _extract_source(source: str, start: str, end: str) -> str:
+    """Slice module source between two anchors, failing loudly if one moved.
+
+    The extracted region ships to Node verbatim, so the anchors must stay
+    unique strings in the module. A refactor that renames or duplicates an
+    anchor fails here with the anchor named, not with an opaque split error.
+    """
+    assert source.count(start) == 1, f"start anchor not unique in source: {start!r}"
+    tail = source.split(start, 1)[1]
+    assert end in tail, f"end anchor not found after start anchor: {end!r}"
+    return start + tail.split(end, 1)[0]
+
+
+def _run_node(source: str) -> dict:
+    proc = subprocess.run(
+        ["node", "--input-type=module"],
+        input=source,
+        capture_output=True,
+        text=True,
+        cwd=_REPO,
+        timeout=30,
+    )
+    assert proc.returncode == 0, proc.stderr
+    # A few imported browser modules log optional-service status at startup.
+    # Keep the runtime smoke honest while reading only its final JSON result.
+    return json.loads(proc.stdout.strip().splitlines()[-1])
+
+
+def _chat_smoke_source(extra_source: str) -> str:
+    """Return chat.js source with its real imports made absolute."""
+
+    def absolute_import(match: re.Match[str]) -> str:
+        relative = match.group("relative")
+        path_part, separator, query = relative.partition("?")
+        target = (_CHAT_PATH.parent / path_part).resolve().as_uri()
+        if separator:
+            target += "?" + query
+        return match.group("prefix") + target + match.group("quote")
+
+    source = re.sub(
+        r"(?P<prefix>from\s+(?P<quote>['\"]))(?P<relative>\./[^'\"]+)(?P=quote)",
+        absolute_import,
+        _CHAT,
+    )
+    source += "\n" + extra_source
+    return source
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_chat_runtime_stream_state_helpers_are_all_callable(tmp_path):
+    """Import the real module and execute all three rebased-away helpers."""
+
+    module_source = _chat_smoke_source(
+        """
+export function __pr6020StreamStateSmoke() {
+  const sid = 'pr6020-runtime-smoke';
+  const controller = { abort() {}, signal: { aborted: false } };
+  const originalGetSessionId = sessionModule.getCurrentSessionId;
+  sessionModule.getCurrentSessionId = () => sid;
+  try {
+    _activeStreams.set(sid, {
+      abortCtrl: controller,
+      holder: { id: 'holder' },
+      lastActivity: 0,
+    });
+    const active = _getForegroundStreamState();
+    const touchedAt = _touchStreamActivity(sid);
+    const synced = _syncForegroundStreamGlobals();
+    return {
+      activeController: active && active.abortCtrl === controller,
+      touched: touchedAt > 0 && _activeStreams.get(sid).lastActivity === touchedAt,
+      synced: synced === active && currentAbort === controller && isStreaming,
+    };
+  } finally {
+    _activeStreams.delete(sid);
+    sessionModule.getCurrentSessionId = originalGetSessionId;
+  }
+}
+"""
+    )
+    module_path = tmp_path / "chat-runtime-smoke.mjs"
+    module_path.write_text(module_source, encoding="utf-8")
+    module_uri = module_path.as_uri()
+    script = f"""
+      globalThis.window = globalThis;
+      globalThis.addEventListener = () => {{}};
+      globalThis.removeEventListener = () => {{}};
+      globalThis.dispatchEvent = () => {{}};
+      globalThis.requestAnimationFrame = () => 0;
+      globalThis.cancelAnimationFrame = () => {{}};
+      globalThis.fetch = async () => ({{
+        ok: false,
+        json: async () => ({{}}),
+        text: async () => '',
+        headers: {{ get() {{ return null; }} }},
+      }});
+      class Element {{
+        constructor() {{
+          this.children = [];
+          this.classList = {{
+            add() {{}}, remove() {{}}, toggle() {{}}, contains() {{ return false; }},
+          }};
+          this.style = {{ setProperty() {{}} }};
+          this.dataset = {{}};
+        }}
+        querySelector() {{ return null; }}
+        querySelectorAll() {{ return []; }}
+        appendChild(child) {{ this.children.push(child); return child; }}
+        addEventListener() {{}}
+        removeEventListener() {{}}
+      }}
+      class HTMLInputElement extends Element {{
+        get value() {{ return this._value || ''; }}
+        set value(value) {{ this._value = value; }}
+      }}
+      globalThis.HTMLInputElement = HTMLInputElement;
+      const root = new Element();
+      globalThis.document = {{
+        body: root,
+        head: root,
+        documentElement: root,
+        getElementById() {{ return null; }},
+        querySelector() {{ return null; }},
+        querySelectorAll() {{ return []; }},
+        createElement(tag) {{ return tag === 'input' ? new HTMLInputElement() : new Element(); }},
+        createTextNode(text) {{ return {{ textContent: text }}; }},
+        addEventListener() {{}},
+        removeEventListener() {{}},
+      }};
+      globalThis.localStorage = {{ getItem() {{ return null; }}, setItem() {{}}, removeItem() {{}} }};
+      globalThis.location = {{}};
+      globalThis.history = {{}};
+      globalThis.MutationObserver = class {{ observe() {{}} }};
+      globalThis.CustomEvent = class {{}};
+      globalThis.Storage = class {{}};
+      const chat = await import({json.dumps(module_uri)});
+      console.log(JSON.stringify(chat.__pr6020StreamStateSmoke()));
+      process.exit(0);
+    """
+
+    assert _run_node(script) == {
+        "activeController": True,
+        "touched": True,
+        "synced": True,
+    }
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_canonical_terminal_followed_by_eof_is_not_auto_recovered():
+    """A persisted terminal marker owns EOF; a plain premature EOF still retries."""
+
+    completion_gate = _extract_source(
+        _CHAT,
+        "if (_streamTerminalError)",
+        "// The final foreground render below is authoritative.",
+    )
+    script = f"""
+      import {{
+        createTerminalStreamError,
+        isRecoverableStreamError,
+      }} from {json.dumps(_STREAM_ERRORS_URI)};
+      function runCompletionGate(canonicalTerminalSaved) {{
+        let _streamTerminalError = null;
+        let _streamSawDone = false;
+        let _canonicalTerminalSaved = canonicalTerminalSaved;
+        try {{
+          {completion_gate}
+          return {{ recovered: false, completed: true }};
+        }} catch (error) {{
+          return {{
+            recovered: isRecoverableStreamError(error),
+            completed: false,
+            terminal: !!error.terminalStreamError,
+            message: error.message,
+          }};
+        }}
+      }}
+      console.log(JSON.stringify({{
+        savedTerminal: runCompletionGate(true),
+        plainEof: runCompletionGate(false),
+      }}));
+    """
+
+    assert _run_node(script) == {
+        # A saved canonical terminal must neither auto-recover nor render as a
+        # clean success: it takes the terminal-error path, whose catch handler
+        # reloads the persisted record.
+        "savedTerminal": {
+            "recovered": False,
+            "completed": False,
+            "terminal": True,
+            "message": "Stream closed after canonical terminal event",
+        },
+        "plainEof": {
+            "recovered": True,
+            "completed": False,
+            "terminal": False,
+            "message": "Stream closed before completion",
+        },
+    }
+
+
+@pytest.mark.asyncio
+async def test_immediate_replacement_closes_subscriber_bound_to_never_started_run():
+    """Cancellation before _drain's first instruction must still terminalize run 1."""
+
+    session_id = "pr6020-immediate-replacement"
+    agent_runs._RUNS.pop(session_id, None)
+
+    async def never_started():
+        yield 'data: {"delta":"old"}\n\n'
+
+    async def replacement():
+        yield 'data: {"delta":"new"}\n\n'
+
+    first = agent_runs.start(session_id, never_started())
+    first_subscription = asyncio.create_task(
+        _collect_run_events(session_id, first)
+    )
+    # Do not yield between starts: first.task is cancelled before _drain gets
+    # its first instruction, exactly the race a rapid double-send creates.
+    second = agent_runs.start(session_id, replacement())
+
+    assert await asyncio.wait_for(first_subscription, timeout=0.5) == []
+    await asyncio.wait_for(second.task, timeout=0.5)
+    assert first.status == "stopped"
+    assert second.status == "done"
+
+
+async def _collect_run_events(session_id: str, run: object) -> list[str]:
+    return [event async for event in agent_runs.subscribe(session_id, run)]
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_stop_before_response_headers_waits_for_exact_run_identity():
+    """Never send headerless Stop, but flush the queued Stop once headers arrive."""
+
+    state_and_stop = _extract_source(
+        _CHAT, "const _backgroundStreams", "// Sources box builder"
+    )
+    header_capture = _extract_source(
+        _CHAT,
+        "const streamRunId = res.headers.get('X-Odysseus-Run-Id')",
+        "// Mark the chat log busy",
+    )
+    script = f"""
+      const calls = [];
+      function _setForegroundChatBusy() {{}}
+      const window = {{}};
+      const sessionModule = {{ getCurrentSessionId() {{ return 'session-1'; }} }};
+      const fetch = async (url, options) => {{ calls.push({{ url, options }}); return {{ ok: true }}; }};
+      {state_and_stop}
+      {{
+        const streamSessionId = 'normal-session';
+        const streamGeneration = 1;
+        _streamGenerations.set(streamSessionId, streamGeneration);
+        const res = {{ headers: {{ get(name) {{
+          return name === 'X-Odysseus-Run-Id' ? 'normal-run' : null;
+        }} }} }};
+        {header_capture}
+      }}
+      await new Promise(resolve => setTimeout(resolve, 0));
+      const normalHeaderCalls = calls.length;
+      let beforeHeaders;
+      {{
+        const streamSessionId = 'session-1';
+        const streamGeneration = 1;
+        _streamGenerations.set(streamSessionId, streamGeneration);
+        _stopExactRun(streamSessionId);
+        beforeHeaders = calls.length;
+        const res = {{ headers: {{ get(name) {{
+          return name === 'X-Odysseus-Run-Id' ? 'run-1' : null;
+        }} }} }};
+        {header_capture}
+      }}
+      await new Promise(resolve => setTimeout(resolve, 0));
+      console.log(JSON.stringify({{
+        normalHeaderCalls,
+        beforeHeaders,
+        calls: calls.map(call => ({{
+          url: call.url,
+          method: call.options.method,
+          runId: call.options.headers['X-Odysseus-Run-Id'],
+        }})),
+      }}));
+    """
+
+    assert _run_node(script) == {
+        "normalHeaderCalls": 0,
+        "beforeHeaders": 0,
+        "calls": [
+            {
+                "url": "/api/chat/stop/session-1",
+                "method": "POST",
+                "runId": "run-1",
+            }
+        ],
+    }
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_timeout_before_response_headers_also_waits_for_exact_run_identity():
+    """The automatic timeout must preserve the POST until its run id arrives."""
+
+    script = f"""
+      {_timeout_harness_prelude()}
+      callbacks[0]();
+      const beforeHeaders = {{ aborted: abortCtrl.signal.aborted, calls: calls.length }};
+      _rememberStreamRunId(streamSessionId, 'run-1', streamGeneration);
+      await Promise.resolve();
+      console.log(JSON.stringify({{
+        beforeHeaders,
+        afterHeaders: {{
+          aborted: abortCtrl.signal.aborted,
+          runId: calls[0] && calls[0].options.headers['X-Odysseus-Run-Id'],
+        }},
+      }}));
+    """
+
+    assert _run_node(script) == {
+        "beforeHeaders": {"aborted": False, "calls": 0},
+        "afterHeaders": {"aborted": True, "runId": "run-1"},
+    }
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_resend_preserves_queued_stop_until_old_run_identity_arrives():
+    """A replacement must not sever the superseded POST's identity channel.
+
+    The queued Stop stays generation-tagged and fires from the OLD send's own
+    header arrival, so the old run is cancelled even when the replacement dies
+    before its POST reaches the server (which is what would otherwise cancel
+    it). The old run id must not leak into the replacement's identity map.
+    """
+
+    state_and_stop = _extract_source(
+        _CHAT, "const _backgroundStreams", "// Sources box builder"
+    )
+    resend_reset = _extract_source(
+        _CHAT,
+        "const streamGeneration = (_streamGenerations.get(streamSessionId) || 0) + 1;",
+        "_sendInFlight = false;",
+    )
+    header_capture = _extract_source(
+        _CHAT,
+        "const streamRunId = res.headers.get('X-Odysseus-Run-Id')",
+        "// Mark the chat log busy",
+    )
+    script = f"""
+      const calls = [];
+      function _setForegroundChatBusy() {{}}
+      const window = {{}};
+      const sessionModule = {{ getCurrentSessionId() {{ return 'session-1'; }} }};
+      const fetch = async (url, options) => {{ calls.push({{ url, options }}); return {{ ok: true }}; }};
+      {state_and_stop}
+      const oldCtrl = {{
+        _reason: '',
+        signal: {{ aborted: false }},
+        abort() {{ this.signal.aborted = true; }},
+      }};
+      // Old send (generation 1) queues a Stop before its headers arrive.
+      _streamGenerations.set('session-1', 1);
+      const oldGeneration = 1;
+      _stopExactRun('session-1', oldCtrl);
+      const queuedBefore = _pendingRunStops.has('session-1:1');
+      // Replacement send starts: bumps the generation, leaves the queued Stop.
+      {{
+        const streamSessionId = 'session-1';
+        {resend_reset}
+      }}
+      // The replacement is ALSO stopped before its headers arrive: both
+      // sends' cancellation intents must coexist, neither displacing the
+      // other (a single session-keyed slot loses the old send's Stop, and
+      // with it the only cancel for that run if this replacement dies
+      // before its own POST reaches the server).
+      const newCtrl = {{
+        _reason: '',
+        signal: {{ aborted: false }},
+        abort() {{ this.signal.aborted = true; }},
+      }};
+      _stopExactRun('session-1', newCtrl);
+      const afterResend = {{
+        oldQueuedKept: _pendingRunStops.has('session-1:1'),
+        newQueued: _pendingRunStops.has('session-1:2'),
+        oldAborted: oldCtrl.signal.aborted,
+        generation: _streamGenerations.get('session-1'),
+      }};
+      // The old POST's headers finally arrive: its queued Stop fires with its
+      // own run id, and the old controller aborts.
+      {{
+        const streamSessionId = 'session-1';
+        const streamGeneration = oldGeneration;
+        const res = {{ headers: {{ get(name) {{
+          return name === 'X-Odysseus-Run-Id' ? 'old-run' : null;
+        }} }} }};
+        {header_capture}
+      }}
+      await new Promise(resolve => setTimeout(resolve, 0));
+      console.log(JSON.stringify({{
+        queuedBefore,
+        afterResend,
+        afterOldHeaders: {{
+          oldQueued: _pendingRunStops.has('session-1:1'),
+          newQueuedKept: _pendingRunStops.has('session-1:2'),
+          oldAborted: oldCtrl.signal.aborted,
+          oldReason: oldCtrl._reason,
+          newAborted: newCtrl.signal.aborted,
+          currentRunIdPolluted: _streamRunIds.has('session-1'),
+          stopCalls: calls.map(call => ({{
+            url: call.url,
+            runId: call.options.headers['X-Odysseus-Run-Id'],
+          }})),
+        }},
+      }}));
+    """
+
+    assert _run_node(script) == {
+        "queuedBefore": True,
+        "afterResend": {
+            "oldQueuedKept": True,
+            "newQueued": True,
+            "oldAborted": False,
+            "generation": 2,
+        },
+        "afterOldHeaders": {
+            "oldQueued": False,
+            # The replacement's own queued Stop must survive the old send's
+            # flush untouched.
+            "newQueuedKept": True,
+            "oldAborted": True,
+            "oldReason": "user-stop",
+            "newAborted": False,
+            # The stale send's run id must not become the replacement's
+            # identity, but its exact Stop must still go out.
+            "currentRunIdPolluted": False,
+            "stopCalls": [
+                {"url": "/api/chat/stop/session-1", "runId": "old-run"}
+            ],
+        },
+    }
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_superseded_stream_cleanup_leaves_replacement_state_alone():
+    """A stale send's finally must not clear state the replacement owns.
+
+    Ownership is decided by generation, which the replacement bumps at its
+    very first synchronous step — so the guard holds even in the window
+    BEFORE the replacement registers its own stream entry (where the old
+    finally still sees its own registration and controller identity alone
+    would call it the owner).
+    """
+
+    state_and_stop = _extract_source(
+        _CHAT, "const _backgroundStreams", "// Sources box builder"
+    )
+    finally_cleanup = _extract_source(
+        _CHAT,
+        "const _ownsStreamState =",
+        "// Streaming done — let screen readers announce",
+    )
+    script = f"""
+      let currentAbort = null;
+      let isStreaming = false;
+      let currentHolder = null;
+      let _sendInFlight = false;
+      function _setForegroundChatBusy() {{}}
+      const window = {{}};
+      const sessionModule = {{ getCurrentSessionId() {{ return 'session-1'; }} }};
+      {state_and_stop}
+      function runCleanup(abortCtrl, streamGeneration) {{
+        const streamSessionId = 'session-1';
+        const _sendState = {{ generation: streamGeneration, abortCtrl }};
+        {finally_cleanup}
+        return _ownsStreamState;
+      }}
+      const oldCtrl = {{ signal: {{ aborted: true }}, abort() {{}} }};
+      const newCtrl = {{ signal: {{ aborted: false }}, abort() {{}} }};
+      // Pre-registration supersession: the replacement bumped the generation
+      // and set the session id, but has NOT registered its stream entry yet —
+      // the old send's own entry is still the one in the map.
+      _streamGenerations.set('session-1', 2);
+      _streamSessionId = 'session-1';
+      _activeStreams.set('session-1', {{ abortCtrl: oldCtrl, holder: null, lastActivity: 1 }});
+      _pendingRunStops.set('session-1:2', newCtrl);
+      const preRegOwns = runCleanup(oldCtrl, 1);
+      const afterPreReg = {{
+        ownEntryRemoved: !_activeStreams.has('session-1'),
+        replacementPendingKept: _pendingRunStops.has('session-1:2'),
+        sessionKept: _streamSessionId === 'session-1',
+      }};
+      // Post-registration supersession: the replacement's entry is in the map.
+      _activeStreams.set('session-1', {{ abortCtrl: newCtrl, holder: null, lastActivity: 2 }});
+      const postRegOwns = runCleanup(oldCtrl, 1);
+      const afterPostReg = {{
+        replacementRegistrationKept: _activeStreams.has('session-1'),
+        replacementPendingKept: _pendingRunStops.has('session-1:2'),
+        sessionKept: _streamSessionId === 'session-1',
+      }};
+      // Owner: the current-generation send cleans up normally.
+      const ownerOwns = runCleanup(newCtrl, 2);
+      const afterOwner = {{
+        registered: _activeStreams.has('session-1'),
+        pendingKept: _pendingRunStops.has('session-1:2'),
+        sessionCleared: _streamSessionId === null,
+      }};
+      console.log(JSON.stringify({{
+        preRegOwns, afterPreReg, postRegOwns, afterPostReg, ownerOwns, afterOwner,
+      }}));
+    """
+
+    assert _run_node(script) == {
+        "preRegOwns": False,
+        "afterPreReg": {
+            "ownEntryRemoved": True,
+            "replacementPendingKept": True,
+            "sessionKept": True,
+        },
+        "postRegOwns": False,
+        "afterPostReg": {
+            "replacementRegistrationKept": True,
+            "replacementPendingKept": True,
+            "sessionKept": True,
+        },
+        "ownerOwns": True,
+        "afterOwner": {
+            "registered": False,
+            "pendingKept": False,
+            "sessionCleared": True,
+        },
+    }
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_real_reservation_supersedes_and_stale_cleanup_keeps_gate_closed():
+    """Drive the REAL send-commit reservation, then a stale send's cleanup.
+
+    The reservation is synchronous, so the previous send is superseded before
+    any await runs; its cleanup must then neither clear session state nor
+    resync the foreground globals (a stale sync would set isStreaming false
+    while _sendInFlight is already false, reopening the send gate before the
+    replacement registers).
+    """
+
+    state_and_stop = _extract_source(
+        _CHAT, "const _backgroundStreams", "// Sources box builder"
+    )
+    reservation = _extract_source(
+        _CHAT,
+        "const streamGeneration = (_streamGenerations.get(streamSessionId) || 0) + 1;",
+        "_sendInFlight = false;",
+    )
+    finally_cleanup = _extract_source(
+        _CHAT,
+        "const _ownsStreamState =",
+        "// Streaming done — let screen readers announce",
+    )
+    script = f"""
+      let currentAbort = null;
+      let isStreaming = true;
+      let currentHolder = null;
+      let _sendInFlight = false;
+      function _setForegroundChatBusy() {{}}
+      const window = {{}};
+      const sessionModule = {{ getCurrentSessionId() {{ return 'session-1'; }} }};
+      {state_and_stop}
+      const oldCtrl = {{ signal: {{ aborted: false }}, abort() {{ this.signal.aborted = true; }} }};
+      // Old send (generation 1) is mid-stream and registered.
+      _streamGenerations.set('session-1', 1);
+      _streamSessionId = 'session-1';
+      _activeStreams.set('session-1', {{ abortCtrl: oldCtrl, holder: null, lastActivity: 1 }});
+      // Replacement commits: run the REAL reservation block synchronously.
+      let installed;
+      {{
+        const streamSessionId = 'session-1';
+        {reservation}
+        installed = {{ generation: streamGeneration, sendState: _sendState }};
+      }}
+      const afterReservation = {{
+        generation: _streamGenerations.get('session-1'),
+        sendStateInstalled: _sendStates.get('session-1') === installed.sendState,
+        controllerPending: installed.sendState.abortCtrl === null,
+      }};
+      // Old send's cleanup runs mid-preflight (before the replacement
+      // registers): it must treat itself as superseded.
+      let staleOwns;
+      {{
+        const streamSessionId = 'session-1';
+        const streamGeneration = 1;
+        const abortCtrl = oldCtrl;
+        const _sendState = {{ generation: 1, abortCtrl: oldCtrl }};
+        {finally_cleanup}
+        staleOwns = _ownsStreamState;
+      }}
+      console.log(JSON.stringify({{
+        afterReservation,
+        staleOwns,
+        afterStaleCleanup: {{
+          sessionKept: _streamSessionId === 'session-1',
+          sendStateKept: _sendStates.get('session-1') === installed.sendState,
+          gateStillClosed: isStreaming === true,
+        }},
+      }}));
+    """
+
+    assert _run_node(script) == {
+        "afterReservation": {
+            "generation": 2,
+            "sendStateInstalled": True,
+            "controllerPending": True,
+        },
+        "staleOwns": False,
+        "afterStaleCleanup": {
+            "sessionKept": True,
+            "sendStateKept": True,
+            # isStreaming untouched because the superseded send skipped the
+            # foreground resync entirely.
+            "gateStillClosed": True,
+        },
+    }
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_stale_preflight_bails_before_creating_controller():
+    """A send superseded during preflight must not proceed to register/POST."""
+
+    state_and_stop = _extract_source(
+        _CHAT, "const _backgroundStreams", "// Sources box builder"
+    )
+    preflight_gate = _extract_source(
+        _CHAT, "// Superseded during preflight", "currentAbort = abortCtrl;"
+    ) + "currentAbort = abortCtrl;"
+    script = f"""
+      let currentAbort = null;
+      let isStreaming = false;
+      let currentHolder = null;
+      let _sendInFlight = false;
+      function _setForegroundChatBusy() {{}}
+      const window = {{}};
+      const document = {{
+        createElement() {{ return {{ style: {{}}, textContent: '' }}; }},
+      }};
+      const sessionModule = {{ getCurrentSessionId() {{ return 'session-1'; }} }};
+      {state_and_stop}
+      function runPreflightGate(streamGeneration, _sendState, _userMsgEl) {{
+        const streamSessionId = 'session-1';
+        let abortCtrl = null;
+        {preflight_gate}
+        return abortCtrl;
+      }}
+      // Stale: generation 1 resumes after generation 2 reserved the session.
+      // Its optimistic user bubble must be marked undelivered, not left as a
+      // ghost that looks sent.
+      _streamGenerations.set('session-1', 2);
+      const staleState = {{ generation: 1, abortCtrl: null }};
+      const staleBubble = {{
+        parentNode: {{}},
+        notes: [],
+        appendChild(node) {{ this.notes.push(node.textContent); }},
+      }};
+      const staleResult = runPreflightGate(1, staleState, staleBubble);
+      // Current: generation 2 proceeds and wires its controller.
+      const currentState = {{ generation: 2, abortCtrl: null }};
+      const currentBubble = {{
+        parentNode: {{}},
+        notes: [],
+        appendChild(node) {{ this.notes.push(node.textContent); }},
+      }};
+      const currentResult = runPreflightGate(2, currentState, currentBubble);
+      console.log(JSON.stringify({{
+        staleBailed: staleResult === undefined,
+        staleControllerNever: staleState.abortCtrl === null,
+        staleBubbleNotes: staleBubble.notes,
+        currentProceeded: !!currentResult,
+        currentWired: currentState.abortCtrl === currentResult && currentAbort === currentResult,
+        currentBubbleNotes: currentBubble.notes,
+      }}));
+    """
+
+    assert _run_node(script) == {
+        "staleBailed": True,
+        "staleControllerNever": True,
+        "staleBubbleNotes": ["[Not sent — superseded by a newer message]"],
+        "currentProceeded": True,
+        "currentWired": True,
+        "currentBubbleNotes": [],
+    }
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_stop_during_replacement_preflight_never_borrows_old_controller():
+    """Stop must take the current send's controller from its send state.
+
+    During the replacement's preflight the stream registry still holds the
+    superseded send's entry; borrowing that controller would abort the only
+    identity channel able to name the old run while queueing a Stop for the
+    new one. A committed-but-pre-POST send has a null controller: the Stop
+    queues under the new generation and nothing is aborted yet.
+    """
+
+    state_and_stop = _extract_source(
+        _CHAT, "const _backgroundStreams", "// Sources box builder"
+    )
+    abort_current = _extract_source(
+        _CHAT, "export function abortCurrentRequest", "// ── Stall watchdog"
+    ).replace("export function", "function")
+    reservation = _extract_source(
+        _CHAT,
+        "const streamGeneration = (_streamGenerations.get(streamSessionId) || 0) + 1;",
+        "_sendInFlight = false;",
+    )
+    script = f"""
+      let currentAbort = null;
+      let isStreaming = false;
+      let currentHolder = null;
+      let _sendInFlight = false;
+      function _setForegroundChatBusy() {{}}
+      const calls = [];
+      const fetch = async (url, options) => {{ calls.push({{ url, options }}); return {{ ok: true }}; }};
+      const window = {{}};
+      const sessionModule = {{ getCurrentSessionId() {{ return 'session-1'; }} }};
+      {state_and_stop}
+      {abort_current}
+      const oldCtrl = {{ signal: {{ aborted: false }}, abort() {{ this.signal.aborted = true; }} }};
+      // Generation 1 is registered, streaming, and its run id is KNOWN — the
+      // exact window daybreak probed: a Stop right after the replacement
+      // commits must not consume the old run identity.
+      _streamGenerations.set('session-1', 1);
+      _streamRunIds.set('session-1', 'old-run');
+      _activeStreams.set('session-1', {{ abortCtrl: oldCtrl, holder: null, lastActivity: 1 }});
+      currentAbort = oldCtrl;
+      // Replacement (generation 2) commits via the REAL reservation block; no
+      // controller exists yet and the model-switch await has not resolved.
+      {{
+        const streamSessionId = 'session-1';
+        {reservation}
+      }}
+      abortCurrentRequest(true);
+      const preRegistration = {{
+        oldRunIdCleared: !_streamRunIds.has('session-1'),
+        queuedForNew: _pendingRunStops.has('session-1:2'),
+        queuedController: _pendingRunStops.get('session-1:2') || null,
+        oldAborted: oldCtrl.signal.aborted,
+        stopCalls: calls.length,
+      }};
+      // Normal case: the current send's own controller, run id known.
+      const ownCtrl = {{ _reason: '', signal: {{ aborted: false }}, abort() {{ this.signal.aborted = true; }} }};
+      _sendStates.set('session-1', {{ generation: 2, abortCtrl: ownCtrl }});
+      _streamRunIds.set('session-1', 'run-2');
+      abortCurrentRequest(true);
+      await new Promise(resolve => setTimeout(resolve, 0));
+      console.log(JSON.stringify({{
+        preRegistration,
+        normal: {{
+          ownAborted: ownCtrl.signal.aborted,
+          oldStillUntouched: oldCtrl.signal.aborted,
+          stopRunId: calls[0] && calls[0].options.headers['X-Odysseus-Run-Id'],
+        }},
+      }}));
+    """
+
+    assert _run_node(script) == {
+        "preRegistration": {
+            # The old run identity dies at reservation: the Stop queues for
+            # the NEW send instead of firing against the old run and skipping
+            # the queue entirely.
+            "oldRunIdCleared": True,
+            "queuedForNew": True,
+            "queuedController": None,
+            "oldAborted": False,
+            "stopCalls": 0,
+        },
+        "normal": {
+            "ownAborted": True,
+            "oldStillUntouched": False,
+            "stopRunId": "run-2",
+        },
+    }
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_timeout_grace_hard_aborts_when_run_identity_never_arrives():
+    """A POST hung before headers is still cancelled by the timeout's grace."""
+
+    script = f"""
+      {_timeout_harness_prelude()}
+      callbacks[0]();
+      const afterTimeout = {{ aborted: abortCtrl.signal.aborted, pending: callbacks.length }};
+      callbacks[1]();
+      console.log(JSON.stringify({{
+        afterTimeout,
+        afterGrace: {{ aborted: abortCtrl.signal.aborted, stopCalls: calls.length }},
+      }}));
+    """
+
+    assert _run_node(script) == {
+        "afterTimeout": {"aborted": False, "pending": 2},
+        "afterGrace": {"aborted": True, "stopCalls": 0},
+    }
+
+
+def _timeout_harness_prelude() -> str:
+    """Shared Node harness: real stop/state and timeout blocks, fake timers."""
+
+    state_and_stop = _extract_source(
+        _CHAT, "const _backgroundStreams", "// Sources box builder"
+    )
+    timeout_setup = _extract_source(
+        _CHAT, "timeoutId = setTimeout(() =>", "}, timeoutMs);"
+    ) + "}, timeoutMs);"
+    return f"""
+      const calls = [];
+      const callbacks = [];
+      function _setForegroundChatBusy() {{}}
+      function setTimeout(callback) {{ callbacks.push(callback); return 1; }}
+      const window = {{}};
+      const sessionModule = {{ getCurrentSessionId() {{ return 'session-1'; }} }};
+      const fetch = async (url, options) => {{ calls.push({{ url, options }}); return {{ ok: true }}; }};
+      const RUN_ID_ABORT_GRACE_MS = 2000;
+      {state_and_stop}
+      const streamSessionId = 'session-1';
+      const streamGeneration = 1;
+      _streamGenerations.set(streamSessionId, streamGeneration);
+      const timeoutMs = 1;
+      let timeoutId;
+      let timedOut = false;
+      const abortCtrl = {{
+        _reason: '',
+        signal: {{ aborted: false }},
+        abort() {{ this.signal.aborted = true; }},
+      }};
+      {timeout_setup}
+    """
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_cost_ledger_serializes_stale_cross_tab_writers():
+    """A stale writer must merge, not overwrite a distinct run recorded by a peer."""
+
+    ledger = _extract_source(
+        _RENDERER, "const _COST_KEY", "/** Create a timestamp span"
+    ).replace("export function", "function")
+    script = f"""
+      const state = {{}};
+      let triggerPeerWrite = true;
+      let lockTail = Promise.resolve();
+      const navigator = {{ locks: {{
+        request(_name, callback) {{
+          const next = lockTail.then(callback);
+          lockTail = next.catch(() => {{}});
+          return next;
+        }},
+      }} }};
+      const window = {{ sessionModule: {{ getCurrentSessionId() {{ return 'session'; }} }} }};
+      const document = {{ getElementById() {{ return null; }} }};
+      function _metricsBillableCost(metrics) {{ return metrics.testCost; }}
+      const peerMetrics = {{ testCost: 0.22, _costRecordId: 'run-b' }};
+      let tabA;
+      let tabB;
+      const localStorage = {{
+        getItem(key) {{
+          const staleSnapshot = state[key] || null;
+          if (key === 'ody-session-cost-runs' && triggerPeerWrite) {{
+            triggerPeerWrite = false;
+            tabB.recordSessionMetricsCost(peerMetrics, 'session');
+          }}
+          return staleSnapshot;
+        }},
+        setItem(key, value) {{ state[key] = value; }},
+      }};
+      function createTab() {{
+        {ledger}
+        return {{ recordSessionMetricsCost }};
+      }}
+      tabA = createTab();
+      tabB = createTab();
+      const metricsA = {{ testCost: 0.11, _costRecordId: 'run-a' }};
+      tabA.recordSessionMetricsCost(metricsA, 'session');
+      const queued = {{
+        recorded: !!metricsA._costRecorded,
+        pending: !!metricsA._costRecordPending,
+      }};
+      await new Promise(resolve => setTimeout(resolve, 0));
+      await lockTail;
+      const runs = JSON.parse(state['ody-session-cost-runs'] || '{{}}').session || {{}};
+      console.log(JSON.stringify({{
+        queued,
+        settled: {{
+          recorded: !!metricsA._costRecorded,
+          pending: !!metricsA._costRecordPending,
+        }},
+        runs,
+      }}));
+    """
+
+    assert _run_node(script) == {
+        # Recorded must not be claimed while the write only sits queued behind
+        # the lock; it flips once the write has actually run.
+        "queued": {"recorded": False, "pending": True},
+        "settled": {"recorded": True, "pending": False},
+        "runs": {"run-a": 0.11, "run-b": 0.22},
+    }

tests/test_pr6020_rebase_regressions.py

@@ -0,0 +1,335 @@
+"""Executable regression coverage for behavior lost in PR #6020's rebase."""
+
+import asyncio
+import json
+
+import src.agent_loop as agent_loop
+
+
+ODY_QWEN = "odysseus-qwen3-4b"
+NOTES_TOOLS = {
+    "manage_notes",
+    "manage_calendar",
+    "manage_tasks",
+    "ask_user",
+    "update_plan",
+}
+
+
+def _collect(generator):
+    async def _run():
+        return [chunk async for chunk in generator]
+
+    return asyncio.run(_run())
+
+
+def _events(chunks):
+    return [
+        json.loads(chunk[6:])
+        for chunk in chunks
+        if chunk.startswith("data: ") and not chunk.startswith("data: [DONE]")
+    ]
+
+
+def _install_route_probe(monkeypatch):
+    prompt_calls = []
+    stream_calls = []
+
+    monkeypatch.setattr(agent_loop, "get_setting", lambda key, default=None: default)
+    monkeypatch.setattr(agent_loop, "get_mcp_manager", lambda: None)
+    monkeypatch.setattr(agent_loop, "estimate_tokens", lambda *args, **kwargs: 10)
+    monkeypatch.setattr(agent_loop, "blocked_tools_for_owner", lambda owner: set())
+    monkeypatch.setattr(
+        agent_loop,
+        "_agent_route_tool_mode",
+        lambda *args, **kwargs: (True, False, False),
+    )
+
+    def fake_build(
+        messages,
+        model,
+        _active_document,
+        _mcp_mgr,
+        disabled_tools=None,
+        **kwargs,
+    ):
+        prompt_calls.append(
+            {
+                "model": model,
+                "relevant_tools": set(kwargs.get("relevant_tools") or set()),
+                "disabled_tools": set(disabled_tools or set()),
+                "workspace": kwargs.get("workspace"),
+            }
+        )
+        return (list(messages), [])
+
+    async def fake_stream(_candidates, _messages, **kwargs):
+        stream_calls.append(kwargs)
+        yield 'data: {"delta": "ok"}\n\n'
+        yield "data: [DONE]\n\n"
+
+    monkeypatch.setattr(agent_loop, "_build_system_prompt", fake_build)
+    monkeypatch.setattr(agent_loop, "stream_llm_with_fallback", fake_stream)
+    return prompt_calls, stream_calls
+
+
+def _run_probe(messages, *, relevant_tools, **kwargs):
+    return _collect(
+        agent_loop.stream_agent_loop(
+            "https://api.example/v1",
+            kwargs.pop("model", ODY_QWEN),
+            messages,
+            max_rounds=1,
+            relevant_tools=set(relevant_tools),
+            _is_teacher_run=True,
+            **kwargs,
+        )
+    )
+
+
+def test_odysseus_notes_mode_clamps_and_reenables_all_personal_managers(monkeypatch):
+    prompt_calls, _ = _install_route_probe(monkeypatch)
+
+    _run_probe(
+        [{"role": "user", "content": "Add buy milk to my notes."}],
+        relevant_tools={"bash", "manage_notes", "manage_calendar", "manage_tasks"},
+        disabled_tools={"manage_notes", "manage_calendar", "manage_tasks"},
+    )
+
+    route = prompt_calls[0]
+    assert route["relevant_tools"] == NOTES_TOOLS
+    assert route["disabled_tools"].isdisjoint(
+        {"manage_notes", "manage_calendar", "manage_tasks"}
+    )
+
+
+def test_odysseus_general_mode_disables_every_tool(monkeypatch):
+    from src.tool_policy import known_tool_names
+
+    prompt_calls, _ = _install_route_probe(monkeypatch)
+
+    _run_probe(
+        [{"role": "user", "content": "Explain the CAP theorem."}],
+        relevant_tools={"bash", "manage_notes", "ask_user"},
+    )
+
+    route = prompt_calls[0]
+    assert route["relevant_tools"] == set()
+    assert known_tool_names() <= route["disabled_tools"]
+
+
+def test_odysseus_calendar_intent_uses_notes_mode(monkeypatch):
+    prompt_calls, _ = _install_route_probe(monkeypatch)
+
+    _run_probe(
+        [{"role": "user", "content": "Add lunch tomorrow to my calendar."}],
+        relevant_tools={"manage_notes", "manage_calendar", "manage_tasks", "bash"},
+    )
+
+    assert prompt_calls[0]["relevant_tools"] == NOTES_TOOLS
+
+
+def test_odysseus_calendar_followup_keeps_notes_mode(monkeypatch):
+    prompt_calls, _ = _install_route_probe(monkeypatch)
+    messages = [
+        {"role": "user", "content": "Add lunch tomorrow to my calendar."},
+        {
+            "role": "assistant",
+            "content": "Done.",
+            "metadata": {
+                "tool_events": [
+                    {
+                        "tool": "manage_calendar",
+                        "command": '{"action":"create_event","summary":"Lunch"}',
+                        "output": "Created event evt-123 at noon.",
+                    }
+                ]
+            },
+        },
+        {"role": "user", "content": "Move it to 3pm."},
+    ]
+
+    _run_probe(
+        messages,
+        relevant_tools={"manage_notes", "manage_calendar", "manage_tasks", "bash"},
+    )
+
+    assert prompt_calls[0]["relevant_tools"] == NOTES_TOOLS
+
+
+def test_agent_route_passes_workspace_to_system_prompt(monkeypatch):
+    prompt_calls, _ = _install_route_probe(monkeypatch)
+
+    _run_probe(
+        [{"role": "user", "content": "Fix the failing test in this project."}],
+        model="gpt-4o",
+        relevant_tools={"bash", "read_file", "apply_patch"},
+        workspace="/tmp/example-repo",
+    )
+
+    assert prompt_calls[0]["workspace"] == "/tmp/example-repo"
+
+
+def test_odysseus_qwen_temperature_is_capped_for_agent_requests(monkeypatch):
+    _, stream_calls = _install_route_probe(monkeypatch)
+
+    _run_probe(
+        [{"role": "user", "content": "Add buy milk to my notes."}],
+        relevant_tools={"manage_notes"},
+        temperature=1.2,
+    )
+
+    assert stream_calls[0]["temperature"] == 0.2
+
+
+def test_qwen_fallback_candidate_gets_capped_temperature(monkeypatch):
+    """A non-qwen primary must not leak its temperature into a qwen fallback."""
+
+    _, stream_calls = _install_route_probe(monkeypatch)
+
+    _run_probe(
+        [{"role": "user", "content": "Explain the CAP theorem."}],
+        model="gpt-4o",
+        relevant_tools={"bash"},
+        temperature=1.2,
+        fallbacks=[("https://qwen.example/v1", ODY_QWEN, {})],
+    )
+
+    assert stream_calls[0]["temperature"] == 1.2
+    factory = stream_calls[0]["candidate_request_factory"]
+    request = asyncio.run(factory(1, "https://qwen.example/v1", ODY_QWEN, {}))
+    assert request["kwargs"]["temperature"] == 0.2
+
+
+def test_non_qwen_fallback_keeps_requested_temperature(monkeypatch):
+    """A qwen primary's 0.2 cap must not leak into a non-qwen fallback."""
+
+    _, stream_calls = _install_route_probe(monkeypatch)
+
+    _run_probe(
+        [{"role": "user", "content": "Add buy milk to my notes."}],
+        relevant_tools={"manage_notes"},
+        temperature=1.2,
+        fallbacks=[("https://backup.example/v1", "gpt-4o", {})],
+    )
+
+    assert stream_calls[0]["temperature"] == 0.2
+    factory = stream_calls[0]["candidate_request_factory"]
+    request = asyncio.run(factory(1, "https://backup.example/v1", "gpt-4o", {}))
+    assert request["kwargs"]["temperature"] == 1.2
+
+
+def test_qwen_notes_fallback_reenables_personal_managers(monkeypatch):
+    """The answering candidate's notes mode must unblock the managers for
+    execution, not just enable them in its own route schemas."""
+
+    _install_route_probe(monkeypatch)
+    stream_round = 0
+    resolve_round = 0
+    seen_exec = {}
+
+    async def fake_stream(_candidates, _messages, **kwargs):
+        nonlocal stream_round
+        stream_round += 1
+        if stream_round == 1:
+            yield (
+                "data: "
+                + json.dumps(
+                    {
+                        "type": "fallback",
+                        "answered_by": ODY_QWEN,
+                        "candidate_index": 1,
+                    }
+                )
+                + "\n\n"
+            )
+            yield 'data: {"delta": "Adding the note."}\n\n'
+        else:
+            yield 'data: {"delta": "Done."}\n\n'
+        yield "data: [DONE]\n\n"
+
+    def fake_resolve(*args, **kwargs):
+        nonlocal resolve_round
+        resolve_round += 1
+        if resolve_round == 1:
+            return ([agent_loop.ToolBlock("manage_notes", "{}")], False, [])
+        return ([], False, [])
+
+    async def fake_execute(block, *args, **kwargs):
+        # Execution is the consumer daybreak's probe showed rejecting the
+        # managers: it receives the shared disabled_tools set, not the
+        # answering route's own tool state.
+        seen_exec["disabled_tools"] = set(kwargs.get("disabled_tools") or [])
+        return ("manage_notes: saved", {"output": "noted", "exit_code": 0})
+
+    monkeypatch.setattr(agent_loop, "stream_llm_with_fallback", fake_stream)
+    monkeypatch.setattr(agent_loop, "_resolve_tool_blocks", fake_resolve)
+    monkeypatch.setattr(agent_loop, "execute_tool_block", fake_execute)
+
+    _collect(
+        agent_loop.stream_agent_loop(
+            "https://api.example/v1",
+            "gpt-4o",
+            [{"role": "user", "content": "Add buy milk to my notes."}],
+            max_rounds=2,
+            relevant_tools={"manage_notes", "manage_calendar", "manage_tasks", "bash"},
+            disabled_tools={"manage_notes", "manage_calendar", "manage_tasks"},
+            fallbacks=[("https://qwen.example/v1", ODY_QWEN, {})],
+            _is_teacher_run=True,
+        )
+    )
+
+    assert seen_exec["disabled_tools"].isdisjoint(
+        {"manage_notes", "manage_calendar", "manage_tasks"}
+    )
+
+
+def test_persisted_mcp_tool_event_keeps_description_and_resolved_name(monkeypatch):
+    _install_route_probe(monkeypatch)
+    stream_round = 0
+    resolve_round = 0
+
+    async def fake_stream(_candidates, _messages, **kwargs):
+        nonlocal stream_round
+        stream_round += 1
+        if stream_round == 1:
+            yield 'data: {"delta": "Calling calendar."}\n\n'
+        else:
+            yield 'data: {"delta": "Finished."}\n\n'
+        yield "data: [DONE]\n\n"
+
+    def fake_resolve(*args, **kwargs):
+        nonlocal resolve_round
+        resolve_round += 1
+        if resolve_round == 1:
+            return ([agent_loop.ToolBlock("mcp", "{}")], False, [])
+        return ([], False, [])
+
+    async def fake_execute(block, *args, **kwargs):
+        assert block.tool_type == "mcp"
+        return (
+            "mcp__calendar__create_event: created team sync",
+            {"output": "Created event evt-456.", "exit_code": 0},
+        )
+
+    monkeypatch.setattr(agent_loop, "stream_llm_with_fallback", fake_stream)
+    monkeypatch.setattr(agent_loop, "_resolve_tool_blocks", fake_resolve)
+    monkeypatch.setattr(agent_loop, "execute_tool_block", fake_execute)
+
+    chunks = _collect(
+        agent_loop.stream_agent_loop(
+            "https://api.example/v1",
+            "gpt-4o",
+            [{"role": "user", "content": "Create the team sync event."}],
+            max_rounds=2,
+            relevant_tools={"mcp"},
+            _is_teacher_run=True,
+        )
+    )
+    metrics = next(
+        event["data"] for event in _events(chunks) if event.get("type") == "metrics"
+    )
+    persisted = metrics["tool_events"][0]
+
+    assert persisted["tool"] == "mcp__calendar__create_event"
+    assert persisted["desc"] == "mcp__calendar__create_event: created team sync"

tests/test_prefs_routes.py

@@ -17,4 +17,26 @@ def test_load_keeps_object_prefs_file(tmp_path, monkeypatch):
     prefs_file.write_text(json.dumps({"theme": "dark"}), encoding="utf-8")
     monkeypatch.setattr(prefs_routes, "PREFS_FILE", str(prefs_file))
 
-    assert prefs_routes._load_for_user("alice") == {"theme": "dark"}
+    assert prefs_routes._load_for_user(None) == {"theme": "dark"}
+    assert prefs_routes._load_for_user("alice") == {}
+
+
+def test_named_preference_write_does_not_copy_flat_fallback_consent(tmp_path, monkeypatch):
+    prefs_file = tmp_path / "user_prefs.json"
+    prefs_file.write_text(json.dumps({
+        "theme": "light",
+        "foreground_fallback_enabled": True,
+        "foreground_model_fallbacks": [
+            {"endpoint_id": "legacy-single-user", "model": "legacy-model"},
+        ],
+    }), encoding="utf-8")
+    monkeypatch.setattr(prefs_routes, "PREFS_FILE", str(prefs_file))
+
+    bob = prefs_routes._load_for_user("bob")
+    bob["theme"] = "dark"
+    prefs_routes._save_for_user("bob", bob)
+
+    raw = prefs_routes._load()
+    assert raw["_users"] == {"bob": {"theme": "dark"}}
+    assert raw["foreground_fallback_enabled"] is True
+    assert raw["foreground_model_fallbacks"][0]["endpoint_id"] == "legacy-single-user"

tests/test_prefs_single_user_no_clobber.py

@@ -6,6 +6,9 @@ every other user's preferences (a realistic ops transition: auth turned off
 on a deployment that previously ran multi-user). It must preserve the other
 users and round-trip the change into the same (first) slot _load_for_user
 reads from.
+
+Foreground fallback keys are the exception: auth-disabled consent is stored
+at the flat root so it can never become consent for the first named owner.
 """
 import json
 
@@ -51,3 +54,58 @@ def test_named_user_save_unaffected(tmp_path, monkeypatch):
     data = json.loads(f.read_text())
     assert data["_users"]["alice"] == {"theme": "light"}
     assert data["_users"]["bob"] == {"theme": "dark"}
+
+
+def test_auth_disabled_fallback_consent_does_not_mutate_first_named_user(
+    tmp_path,
+    monkeypatch,
+):
+    f = tmp_path / "user_prefs.json"
+    f.write_text(json.dumps({"_users": {
+        "alice": {"theme": "light"},
+        "bob": {"theme": "paper"},
+    }}), encoding="utf-8")
+    monkeypatch.setattr(pr, "PREFS_FILE", str(f))
+
+    current = pr._load_for_user(None)
+    current["foreground_fallback_enabled"] = True
+    current["foreground_model_fallbacks"] = [
+        {"endpoint_id": "single-user", "model": "single-model"},
+    ]
+    pr._save_for_user(None, current)
+
+    data = json.loads(f.read_text(encoding="utf-8"))
+    assert data["foreground_fallback_enabled"] is True
+    assert data["foreground_model_fallbacks"][0]["endpoint_id"] == "single-user"
+    assert data["_users"]["alice"] == {"theme": "light"}
+    assert data["_users"]["bob"] == {"theme": "paper"}
+
+
+def test_auth_disabled_save_preserves_named_fallback_consent(tmp_path, monkeypatch):
+    f = tmp_path / "user_prefs.json"
+    alice_fallbacks = [{"endpoint_id": "alice", "model": "alice-model"}]
+    f.write_text(json.dumps({"_users": {
+        "alice": {
+            "theme": "light",
+            "foreground_fallback_enabled": True,
+            "foreground_model_fallbacks": alice_fallbacks,
+        },
+    }}), encoding="utf-8")
+    monkeypatch.setattr(pr, "PREFS_FILE", str(f))
+
+    current = pr._load_for_user(None)
+    assert "foreground_fallback_enabled" not in current
+    assert "foreground_model_fallbacks" not in current
+    current["theme"] = "dark"
+    current["foreground_fallback_enabled"] = False
+    current["foreground_model_fallbacks"] = []
+    pr._save_for_user(None, current)
+
+    data = json.loads(f.read_text(encoding="utf-8"))
+    assert data["foreground_fallback_enabled"] is False
+    assert data["foreground_model_fallbacks"] == []
+    assert data["_users"]["alice"] == {
+        "theme": "dark",
+        "foreground_fallback_enabled": True,
+        "foreground_model_fallbacks": alice_fallbacks,
+    }

tests/test_resolve_endpoint_fallbacks.py

@@ -3,8 +3,16 @@
 import json
 from types import SimpleNamespace
 
+import pytest
+
 import src.endpoint_resolver as endpoint_resolver
-from src.endpoint_resolver import resolve_endpoint
+from src.endpoint_resolver import (
+    endpoint_cost_tracked,
+    resolve_endpoint,
+    resolve_endpoint_by_id,
+    resolve_fallback_entries,
+    resolve_fallback_entries_with_descriptors,
+)
 
 
 class _FakeColumn:
@@ -34,6 +42,9 @@ class _FakeQuery:
     def first(self):
         return self.rows[0] if self.rows else None
 
+    def all(self):
+        return list(self.rows)
+
 
 class _FakeDb:
     def __init__(self, rows):
@@ -49,6 +60,7 @@ class _FakeDb:
 def _endpoint(ep_id, model, *, hidden=None):
     return SimpleNamespace(
         id=ep_id,
+        name=f"Endpoint {ep_id}",
         base_url=f"https://{ep_id}.example/v1",
         api_key=f"key-{ep_id}",
         cached_models=json.dumps([model]),
@@ -191,3 +203,140 @@ def test_hidden_configured_model_selects_first_enabled_chat_model(monkeypatch):
     assert url == "https://default.example/v1/chat/completions"
     assert model == "enabled-chat"
     assert headers == {"Authorization": "Bearer key-default"}
+
+
+def test_exact_fallback_drops_hidden_model_instead_of_substituting(monkeypatch):
+    endpoint = SimpleNamespace(
+        id="fallback",
+        base_url="https://fallback.example/v1",
+        api_key="key-fallback",
+        cached_models=json.dumps(["chosen-hidden", "different-live"]),
+        hidden_models=json.dumps(["chosen-hidden"]),
+        is_enabled=True,
+    )
+    _install_resolver_fakes(monkeypatch, {}, [endpoint])
+
+    assert resolve_endpoint_by_id(
+        "fallback",
+        "chosen-hidden",
+        require_exact_model=True,
+    ) is None
+    assert resolve_endpoint_by_id("fallback", "chosen-hidden")[1] == "different-live"
+
+
+def test_exact_fallback_drops_known_missing_model(monkeypatch):
+    _install_resolver_fakes(monkeypatch, {}, [_endpoint("fallback", "known-live")])
+
+    assert resolve_endpoint_by_id(
+        "fallback",
+        "unlisted-model",
+        require_exact_model=True,
+    ) is None
+
+
+def test_fallback_entry_resolution_preserves_credential_distinct_endpoints(monkeypatch):
+    seen = []
+
+    def fake_resolve(ep_id, model, owner=None, *, require_exact_model=False):
+        seen.append((ep_id, model, owner, require_exact_model))
+        return (
+            "https://provider.example/v1/chat/completions",
+            model,
+            {"Authorization": f"Bearer {ep_id}"},
+        )
+
+    monkeypatch.setattr(endpoint_resolver, "resolve_endpoint_by_id", fake_resolve)
+    entries = [
+        {"endpoint_id": "key-one", "model": "same-model"},
+        {"endpoint_id": "key-two", "model": "same-model"},
+    ]
+
+    assert resolve_fallback_entries(
+        entries,
+        owner="alice",
+        require_exact_model=True,
+    ) == [
+        ("https://provider.example/v1/chat/completions", "same-model", {"Authorization": "Bearer key-one"}),
+        ("https://provider.example/v1/chat/completions", "same-model", {"Authorization": "Bearer key-two"}),
+    ]
+    assert seen == [
+        ("key-one", "same-model", "alice", True),
+        ("key-two", "same-model", "alice", True),
+    ]
+
+
+def test_descriptor_resolution_preserves_safe_endpoint_identity(monkeypatch):
+    _install_resolver_fakes(monkeypatch, {}, [_endpoint("backup", "backup-model")])
+
+    routes = resolve_fallback_entries_with_descriptors(
+        [{"endpoint_id": "backup", "model": "backup-model"}],
+        require_exact_model=True,
+    )
+
+    assert routes == [(
+        (
+            "https://backup.example/v1/chat/completions",
+            "backup-model",
+            {"Authorization": "Bearer key-backup"},
+        ),
+        {
+            "endpoint_id": "backup",
+            "endpoint_label": "Endpoint backup",
+            "endpoint_cost_tracked": True,
+        },
+    )]
+
+
+def test_exact_id_descriptor_wins_when_routes_are_identical(monkeypatch):
+    first = _endpoint("account-one", "same-model")
+    second = _endpoint("account-two", "same-model")
+    for endpoint in (first, second):
+        endpoint.base_url = "https://provider.example/v1"
+        endpoint.api_key = "shared-key"
+    _install_resolver_fakes(monkeypatch, {}, [first, second])
+
+    import src.auth_helpers as auth_helpers
+
+    seen_owners = []
+
+    def scoped(query, model_cls, owner, *, include_shared=True):
+        seen_owners.append(owner)
+        return query
+
+    monkeypatch.setattr(auth_helpers, "owner_filter", scoped)
+    resolver = getattr(endpoint_resolver, "resolve_route_descriptor_by_id", None)
+
+    assert resolver is not None
+    assert resolver(
+        "account-two",
+        "https://provider.example/v1/chat/completions",
+        "same-model",
+        {"Authorization": "Bearer shared-key"},
+        owner="alice",
+    ) == {
+        "endpoint_id": "account-two",
+        "endpoint_label": "Endpoint account-two",
+        "endpoint_cost_tracked": True,
+    }
+    assert seen_owners == ["alice"]
+
+
+def test_endpoint_cost_tracking_is_non_secret_route_classification():
+    assert endpoint_cost_tracked("http://localhost:11434/v1") is False
+    assert endpoint_cost_tracked("http://model-service:8000/v1") is False
+    assert endpoint_cost_tracked("http://192.168.1.20:8000/v1") is False
+    assert endpoint_cost_tracked("https://chatgpt.com/backend-api/codex") is False
+    assert endpoint_cost_tracked("https://api.example.com/v1") is True
+    assert endpoint_cost_tracked("http://192.168.1.20:8000/v1", "api") is True
+    assert endpoint_cost_tracked("https://api.example.com/v1", "local") is False
+
+
+@pytest.mark.parametrize(
+    ("url", "expected"),
+    [
+        ("https://[2606:4700:4700::1111]/v1", True),
+        ("http://169.254.10.20:8000/v1", False),
+    ],
+)
+def test_endpoint_cost_tracking_classifies_public_ipv6_and_link_local_ipv4(url, expected):
+    assert endpoint_cost_tracked(url) is expected

tests/test_resolve_session_auth_chatgpt.py

@@ -163,53 +163,3 @@ def test_chatgpt_subscription_clears_previously_persisted_bearer(monkeypatch):
         )
     finally:
         db.close()
-
-
-def test_chatgpt_subscription_fallback_auth_is_not_written_to_sessions_table(monkeypatch):
-    """Fallback endpoint selection must keep the resolved bearer request-local."""
-    TestSessionLocal = _mem_db(monkeypatch)
-    db = TestSessionLocal()
-    try:
-        db.add(ModelEndpoint(
-            id="ep1", name="ChatGPT Subscription", base_url=_CODEX_BASE,
-            provider_auth_id="auth1", owner="alice", is_enabled=True, api_key=None,
-            cached_models='["gpt-5.1-codex"]',
-        ))
-        db.add(DbSession(
-            id="sess1", name="chat", endpoint_url="https://old.example/v1",
-            model="old-model", owner="alice", headers={},
-        ))
-        db.commit()
-    finally:
-        db.close()
-
-    monkeypatch.setattr(
-        endpoint_resolver,
-        "resolve_endpoint_runtime",
-        lambda ep, owner=None: (_CODEX_BASE, "live-access-token"),
-    )
-
-    sess = types.SimpleNamespace(
-        id="sess1", endpoint_url="https://old.example/v1", model="old-model",
-        owner="alice", headers={},
-    )
-    result = chat_helpers.try_fallback_endpoint(sess, "sess1")
-
-    assert result == {
-        "model": "gpt-5.1-codex",
-        "endpoint_url": _CODEX_BASE + "/responses",
-        "endpoint_name": "ChatGPT Subscription",
-    }
-    assert sess.headers["Authorization"] == "Bearer live-access-token"
-
-    db = TestSessionLocal()
-    try:
-        row = db.query(DbSession).filter(DbSession.id == "sess1").first()
-        assert row.model == "gpt-5.1-codex"
-        assert row.endpoint_url == _CODEX_BASE + "/responses"
-        stored = row.headers or {}
-        assert not any(k.lower() == "authorization" for k in stored), (
-            f"ChatGPT fallback bearer leaked into sessions table: {stored}"
-        )
-    finally:
-        db.close()

tests/test_retired_settings_interfaces.py

@@ -0,0 +1,119 @@
+"""Retired settings stay stored but cannot leak through generic interfaces."""
+
+import asyncio
+import json
+from types import SimpleNamespace
+
+import pytest
+
+import core.database as database
+import routes.auth_routes as auth_routes
+import src.settings as settings_mod
+from src.agent_tools.admin_tools import do_manage_settings
+
+
+LEGACY_VALUE = [
+    {"endpoint_id": "private-endpoint-id", "model": "private-model-name"},
+]
+
+
+class _AuthManager:
+    def get_username_for_token(self, token):
+        return "admin" if token == "admin-session" else None
+
+    def is_admin(self, username):
+        return username == "admin"
+
+
+class _Request(SimpleNamespace):
+    def __init__(self, body=None, *, admin=False):
+        super().__init__(
+            cookies={
+                auth_routes.SESSION_COOKIE: "admin-session"
+            } if admin else {},
+            _body=body,
+        )
+
+    async def json(self):
+        return self._body
+
+
+def _route(router, path, method):
+    return next(
+        route.endpoint
+        for route in router.routes
+        if route.path == path and method in route.methods
+    )
+
+
+@pytest.mark.asyncio
+async def test_generic_settings_hide_and_preserve_retired_fallbacks(monkeypatch):
+    store = {
+        **settings_mod.DEFAULT_SETTINGS,
+        "default_model_fallbacks": list(LEGACY_VALUE),
+        "tts_enabled": True,
+    }
+
+    monkeypatch.setattr(auth_routes, "migrate_from_settings", lambda: None)
+    monkeypatch.setattr(auth_routes, "_load_settings", lambda: dict(store))
+
+    def save_settings(updated):
+        store.clear()
+        store.update(updated)
+
+    monkeypatch.setattr(auth_routes, "_save_settings", save_settings)
+    router = auth_routes.setup_auth_routes(_AuthManager())
+    get_settings = _route(router, "/api/auth/settings", "GET")
+    set_settings = _route(router, "/api/auth/settings", "POST")
+
+    anonymous = await get_settings(_Request())
+    admin = await get_settings(_Request(admin=True))
+
+    assert "default_model_fallbacks" not in anonymous
+    assert "default_model_fallbacks" not in admin
+    assert store["default_model_fallbacks"] == LEGACY_VALUE
+
+    response = await set_settings(_Request({
+        "default_model_fallbacks": [],
+        "tts_enabled": False,
+    }, admin=True))
+
+    assert "default_model_fallbacks" not in response
+    assert store["default_model_fallbacks"] == LEGACY_VALUE
+    assert store["tts_enabled"] is False
+
+
+def test_manage_settings_tombstones_legacy_fallback_key(monkeypatch):
+    store = {
+        **settings_mod.DEFAULT_SETTINGS,
+        "default_model_fallbacks": list(LEGACY_VALUE),
+    }
+    save_calls = []
+
+    class _Db:
+        def close(self):
+            return None
+
+    monkeypatch.setattr(database, "SessionLocal", lambda: _Db())
+    monkeypatch.setattr(settings_mod, "load_settings", lambda: dict(store))
+
+    def save_settings(updated):
+        save_calls.append(dict(updated))
+        store.clear()
+        store.update(updated)
+
+    monkeypatch.setattr(settings_mod, "save_settings", save_settings)
+
+    listed = asyncio.run(do_manage_settings(json.dumps({"action": "list"})))
+    assert "default_model_fallbacks" not in listed["settings"]
+
+    for action in ("get", "set", "reset", "delete"):
+        payload = {"action": action, "key": "default_model_fallbacks"}
+        if action == "set":
+            payload["value"] = []
+        result = asyncio.run(do_manage_settings(json.dumps(payload)))
+        assert result["exit_code"] == 1
+        assert "Unknown setting" in result["error"]
+
+    assert save_calls == []
+    assert store["default_model_fallbacks"] == LEGACY_VALUE

tests/test_tool_support_heuristic.py

@@ -6,8 +6,15 @@ Verifies two critical cases:
   2. api.deepseek.com must still be treated as tool-capable via the host
      allow-list (_API_HOSTS), so cloud deepseek users keep working.
 """
+from types import SimpleNamespace
+
 import pytest
-from src.agent_loop import _API_HOSTS, _endpoint_lookup_keys, _is_ollama_openai_compat_url
+from src.agent_loop import (
+    _API_HOSTS,
+    _agent_route_tool_mode,
+    _endpoint_lookup_keys,
+    _is_ollama_openai_compat_url,
+)
 from src.llm_core import _is_ollama_native_url
 
 
@@ -164,3 +171,57 @@ class TestEndpointLookupKeys:
         keys = _endpoint_lookup_keys("http://host.docker.internal:11434/api/chat")
 
         assert "http://host.docker.internal:11434/api" in keys
+
+
+def test_route_tool_mode_matches_credential_distinct_endpoint(monkeypatch):
+    from core import database
+    from src import endpoint_resolver
+
+    rows = [
+        SimpleNamespace(
+            id="one",
+            base_url="https://same.example/v1",
+            api_key="key-one",
+            provider_auth_id=None,
+            supports_tools=True,
+        ),
+        SimpleNamespace(
+            id="two",
+            base_url="https://same.example/v1",
+            api_key="key-two",
+            provider_auth_id=None,
+            supports_tools=False,
+        ),
+    ]
+
+    class Query:
+        def filter(self, *args, **kwargs):
+            return self
+
+        def all(self):
+            return rows
+
+    class Db:
+        def query(self, *args, **kwargs):
+            return Query()
+
+        def close(self):
+            return None
+
+    monkeypatch.setattr(database, "SessionLocal", lambda: Db())
+    monkeypatch.setattr(
+        endpoint_resolver,
+        "resolve_endpoint_runtime",
+        lambda endpoint, owner=None: (endpoint.base_url, endpoint.api_key),
+    )
+
+    assert _agent_route_tool_mode(
+        "https://same.example/v1",
+        "custom-model",
+        headers={"Authorization": "Bearer key-one"},
+    )[0] is True
+    assert _agent_route_tool_mode(
+        "https://same.example/v1",
+        "custom-model",
+        headers={"Authorization": "Bearer key-two"},
+    )[0] is False

tests/test_user_time.py

@@ -117,6 +117,31 @@ def test_agent_system_prompt_includes_shared_current_time(monkeypatch):
     assert "Australia/Brisbane, UTC+10:00" in datetime_messages[0]["content"]
 
 
+def test_route_prompt_rebuild_restores_leading_user_system_message(monkeypatch):
+    import src.agent_loop as agent_loop
+
+    monkeypatch.setattr(agent_loop, "_build_base_prompt", lambda *args, **kwargs: ("AGENT PROMPT", ""))
+    monkeypatch.setattr(agent_loop, "set_active_model", lambda model: None)
+    monkeypatch.setattr(agent_loop, "get_builtin_overrides", lambda: {})
+    monkeypatch.setattr(agent_loop, "_cached_base_prompt", None)
+    monkeypatch.setattr(agent_loop, "_cached_base_prompt_key", None)
+
+    original = [
+        {"role": "system", "content": "USER PERSONA"},
+        {"role": "user", "content": "hello"},
+    ]
+    built, _ = agent_loop._build_system_prompt(
+        original,
+        model="selected-model",
+        active_document=None,
+        mcp_mgr=None,
+    )
+
+    assert built[0]["content"] == "USER PERSONA\n\nAGENT PROMPT"
+    assert built[0]["_agent_injected"] == "merged_prompt"
+    assert agent_loop._strip_agent_injected_messages(built) == original
+
+
 def test_calendar_relative_time_parser_handles_dotted_pm(monkeypatch):
     import routes.calendar_routes as calendar_routes