fix(agent): drop the empty assistant turn from an approved-action replay

The approved-action replay appends the sealed tool result with no assistant
prose for that round, which produced an assistant message with content "".
Anthropic's Messages API rejects a non-final assistant message with empty
content, so a resumed turn after a tool approval failed before the model saw
the result. A turn carrying neither prose nor reasoning has nothing to say to
any provider, so it is no longer appended. A round with prose, and a
reasoning-only round that DeepSeek thinking mode needs, both still append.

routes/cookbook_helpers.py

@@ -1204,6 +1204,41 @@ def _safe_env_prefix(ep: str | None) -> str | None:
     return f'[ -f "{path}" ] && source "{path}" || true'
 
 
+def _local_windows_bash_env_prefix(ep: str | None) -> str | None:
+    """Convert a frontend PowerShell venv prefix for the local Git Bash runner."""
+    if not ep:
+        return ep
+
+    prefix = ep.strip()
+    if not prefix.startswith("&"):
+        return ep
+
+    raw_path = prefix[1:].lstrip()
+    if not raw_path:
+        return ep
+    if raw_path.startswith("'"):
+        if len(raw_path) < 2 or not raw_path.endswith("'"):
+            return ep
+        quoted_path = raw_path[1:-1]
+        if "'" in quoted_path.replace("''", ""):
+            return ep
+        path = quoted_path.replace("''", "'")
+    else:
+        path = raw_path.rstrip()
+        if "'" in path or '"' in path:
+            return ep
+    if any(c in path for c in "\r\n;&|`$<>"):
+        return ep
+    if not path.replace("\\", "/").casefold().endswith("/scripts/activate.ps1"):
+        return ep
+
+    bash_path = _git_bash_path(path)
+    if "\\" in bash_path:
+        return ep
+    bash_path = bash_path[: -len("Activate.ps1")] + "activate"
+    return "source " + shlex.quote(bash_path)
+
+
 def _ssh_ps(host, script_path, port=None):
     """Build SSH command to run a PowerShell script on a Windows remote."""
     pf = f"-p {port} " if port and port != "22" else ""

routes/cookbook_routes.py

@@ -50,7 +50,7 @@ from routes.cookbook_helpers import (
     _SESSION_ID_RE, _validate_repo_id, _validate_serve_model_id, _validate_include, _validate_token,
     _validate_local_dir, _validate_gpus, _shell_path,
     _ps_squote, _bash_squote, _validate_serve_cmd, _parse_serve_phase, OLLAMA_MISSING_HINT,
-    _safe_env_prefix, _local_tooling_path_export, _append_serve_preflight_exit_lines,
+    _safe_env_prefix, _local_windows_bash_env_prefix, _local_tooling_path_export, _append_serve_preflight_exit_lines,
     _append_serve_exit_code_lines, _append_llama_cpp_linux_accel_build_lines, _cached_model_scan_script,
     load_stored_hf_token,
     _append_vllm_linux_preflight_lines, _ollama_bind_from_cmd, _pip_install_fallback_chain,
@@ -1336,7 +1336,7 @@ def setup_cookbook_routes() -> APIRouter:
             # Local: run hf download in the background (tmux on POSIX, a detached
             # process + logfile on Windows where tmux doesn't exist).
             if req.env_prefix:
-                lines.append(_safe_env_prefix(req.env_prefix))
+                lines.append(_safe_env_prefix(_local_windows_bash_env_prefix(req.env_prefix) if local_windows else req.env_prefix))
             else:
                 lines.append("deactivate 2>/dev/null; hash -r")
             # Show whether the HF token reached this run (masked) — tells a gated
@@ -2166,7 +2166,7 @@ def setup_cookbook_routes() -> APIRouter:
             if req.gpus:
                 runner_lines.append(f"export CUDA_VISIBLE_DEVICES='{req.gpus}'")
             if req.env_prefix:
-                runner_lines.append(_safe_env_prefix(req.env_prefix))
+                runner_lines.append(_safe_env_prefix(_local_windows_bash_env_prefix(req.env_prefix) if local_windows else req.env_prefix))
             else:
                 runner_lines.append("deactivate 2>/dev/null; hash -r")
             _append_venv_nvidia_library_path_lines(runner_lines, cmd=req.cmd)

src/agent_loop.py

@@ -3081,10 +3081,17 @@ def _append_tool_results(
             messages.append(result_message)
     else:
         tool_output_text = "\n\n".join(tool_results)
-        msg = {"role": "assistant", "content": round_response}
-        if round_reasoning:
-            msg["reasoning_content"] = round_reasoning
-        messages.append(msg)
+        # An approved-action replay injects the sealed tool result with no
+        # assistant prose for that round, which used to append an assistant turn
+        # whose content was "". Anthropic's Messages API rejects a non-final
+        # assistant message with empty content (HTTP 400), so the resumed turn
+        # died before the model saw the result. A turn carrying neither prose nor
+        # reasoning has nothing to say to any provider, so skip it entirely.
+        if round_response.strip() or round_reasoning:
+            msg = {"role": "assistant", "content": round_response}
+            if round_reasoning:
+                msg["reasoning_content"] = round_reasoning
+            messages.append(msg)
         # Tool output (shell/python stdout, file reads, fetched pages, email
         # bodies, MCP results) is sourced from outside the server. Wrap it as
         # untrusted data so prompt-injection inside a tool result is treated as

static/js/cookbookDownload.js

@@ -15,6 +15,7 @@ let _getPlatform;
 let _serverByVal;
 let _isWindows;
 let _buildEnvPrefix;
+let _psQuote;
 let _buildServeCmd;
 let _detectBackend;
 let _detectToolParser;
@@ -538,7 +539,7 @@ export async function _runModelDownload(panel, model, backend, hostOverride) {
   if (srv.downloadDir) payload.local_dir = srv.downloadDir;
   if (isWin) {
     if (env === 'venv' && envPath) {
-      payload.env_prefix = '& ' + (envPath.endsWith('\\Scripts\\Activate.ps1') ? envPath : envPath + '\\Scripts\\Activate.ps1');
+      payload.env_prefix = '& ' + _psQuote(envPath.endsWith('\\Scripts\\Activate.ps1') ? envPath : envPath + '\\Scripts\\Activate.ps1');
     } else if (env === 'conda' && envPath) {
       payload.env_prefix = 'conda activate ' + envPath;
     }
@@ -652,6 +653,7 @@ export function initDownload(shared) {
   _serverByVal = shared._serverByVal;
   _isWindows = shared._isWindows;
   _buildEnvPrefix = shared._buildEnvPrefix;
+  _psQuote = shared._psQuote;
   _buildServeCmd = shared._buildServeCmd;
   _detectBackend = shared._detectBackend;
   _detectToolParser = shared._detectToolParser;

static/js/cookbookRunning.js

@@ -338,6 +338,7 @@ let _sshPrefix;
 let _getPlatform;
 let _isWindows;
 let _buildEnvPrefix;
+let _psQuote;
 let _loadPresets;
 let _savePresets;
 let _copyText;
@@ -1971,7 +1972,7 @@ export async function _launchServeTask(shortName, repo, cmd, fields, hostOverrid
   let envPrefix = '';
   if (_isWindows()) {
     if (_envState.env === 'venv' && _envState.envPath) {
-      envPrefix = '& ' + (_envState.envPath.endsWith('\\Scripts\\Activate.ps1') ? _envState.envPath : _envState.envPath + '\\Scripts\\Activate.ps1');
+      envPrefix = '& ' + _psQuote(_envState.envPath.endsWith('\\Scripts\\Activate.ps1') ? _envState.envPath : _envState.envPath + '\\Scripts\\Activate.ps1');
     } else if (_envState.env === 'conda' && _envState.envPath) {
       envPrefix = 'conda activate ' + _envState.envPath;
     }
@@ -4402,6 +4403,7 @@ export function initRunning(shared) {
   _getPlatform = shared._getPlatform;
   _isWindows = shared._isWindows;
   _buildEnvPrefix = shared._buildEnvPrefix;
+  _psQuote = shared._psQuote;
   _loadPresets = shared._loadPresets;
   _savePresets = shared._savePresets;
   _copyText = shared._copyText;

tests/test_approved_replay_message_shape.py

@@ -0,0 +1,100 @@
+"""Regression coverage for the assistant turn an approved-action replay appends.
+
+Anthropic's Messages API rejects a non-final assistant message whose content is
+empty, so the resumed turn after a tool approval used to fail before the model
+ever saw the sealed result. The replay injects its result with no assistant
+prose for that round, which is the only path that produced such a turn.
+"""
+
+import src.llm_core as llm_core
+from src.agent_loop import _append_tool_results
+
+_RESULT = "bash: ok\nhello"
+_RECORD = {
+    "tool_name": "bash",
+    "content": "printf hello",
+    "result": {"output": "hello", "exit_code": 0},
+    "text": _RESULT,
+}
+
+
+def _replay_messages(round_response="", round_reasoning=""):
+    """Mirror the approved-action injection in stream_agent_loop."""
+    messages = [
+        {"role": "system", "content": "system preface"},
+        {"role": "user", "content": "run the command and summarise it"},
+    ]
+    _append_tool_results(
+        messages,
+        round_response,
+        [],
+        [_RESULT],
+        [_RESULT],
+        False,
+        0,
+        round_reasoning=round_reasoning,
+        tool_result_records=[_RECORD],
+    )
+    return messages
+
+
+def _empty_assistant_turns(messages):
+    return [
+        index
+        for index, message in enumerate(messages)
+        if message.get("role") == "assistant"
+        and not str(message.get("content") or "").strip()
+        and not message.get("tool_calls")
+    ]
+
+
+def test_replay_appends_no_empty_assistant_turn():
+    assert _empty_assistant_turns(_replay_messages()) == []
+
+
+def test_replay_payload_is_a_single_non_empty_user_turn_for_anthropic():
+    # Asserting the whole sequence rather than scanning a slice: once the empty
+    # spacer is gone the payload is one message, so a "no offenders in
+    # chat[:-1]" check would pass without inspecting anything.
+    sanitized = llm_core._sanitize_llm_messages(_replay_messages())
+    payload = llm_core._build_anthropic_payload(
+        "claude-sonnet-5", sanitized, 0.2, 512
+    )
+    chat = payload["messages"]
+    assert [message["role"] for message in chat] == ["user"]
+    assert all(str(message.get("content") or "").strip() for message in chat)
+
+
+def test_replay_merges_tool_output_after_the_request_with_its_fence_intact():
+    # Dropping the empty assistant turn leaves two adjacent user messages, which
+    # the sanitizer merges. Pin that shape: the tool output must still sit
+    # behind its untrusted fence and must not precede the operator's request.
+    sanitized = llm_core._sanitize_llm_messages(_replay_messages())
+    user_turns = [m for m in sanitized if m.get("role") == "user"]
+    assert len(user_turns) == 1
+    merged = user_turns[0]["content"]
+    assert merged.index("run the command") < merged.index("UNTRUSTED SOURCE DATA")
+    assert merged.index("UNTRUSTED SOURCE DATA") < merged.index("hello")
+
+
+def test_a_round_with_prose_still_appends_its_assistant_turn():
+    messages = _replay_messages(round_response="running that now")
+    assistants = [m for m in messages if m.get("role") == "assistant"]
+    assert [m["content"] for m in assistants] == ["running that now"]
+
+
+def test_reasoning_only_round_keeps_its_carrier_and_its_known_empty_content():
+    """Characterises the one empty-content turn this change deliberately leaves.
+
+    A round with reasoning and no prose still appends its carrier, and that
+    carrier's content is still "", which Anthropic would still reject. Dropping
+    it would lose the reasoning DeepSeek thinking mode requires on the next
+    request, and the approval replay never takes this path because it passes no
+    reasoning. Left alone on purpose; this test makes the gap visible instead of
+    silent, and should be updated by whoever closes it.
+    """
+    messages = _replay_messages(round_reasoning="thinking about it")
+    assistants = [m for m in messages if m.get("role") == "assistant"]
+    assert len(assistants) == 1
+    assert assistants[0].get("reasoning_content") == "thinking about it"
+    assert assistants[0]["content"] == ""

tests/test_cookbook_helpers.py

@@ -16,6 +16,7 @@ from routes.cookbook_helpers import (
     _llama_cpp_rebuild_cmd,
     _append_vllm_linux_preflight_lines,
     _local_tooling_path_export,
+    _local_windows_bash_env_prefix,
     _pip_install_attempt,
     _pip_install_fallback_chain,
     _ollama_bind_from_cmd,
@@ -107,6 +108,70 @@ def test_safe_env_prefix_accepts_powershell_activation_path():
     )
 
 
+@pytest.mark.parametrize(
+    ("prefix", "expected"),
+    [
+        ("& 'C:\\Users\\me\\venv\\Scripts\\Activate.ps1'", "source /c/Users/me/venv/Scripts/activate"),
+        (r"& C:\Users\me\venv\Scripts\Activate.ps1", "source /c/Users/me/venv/Scripts/activate"),
+        (
+            r"& C:\Users\me\My Envs\venv\Scripts\Activate.ps1",
+            "source '/c/Users/me/My Envs/venv/Scripts/activate'",
+        ),
+        (
+            "& 'C:\\Users\\me\\My Envs\\venv\\Scripts\\Activate.ps1'",
+            "source '/c/Users/me/My Envs/venv/Scripts/activate'",
+        ),
+        (r"& D:/Envs/venv/Scripts/Activate.ps1", "source /d/Envs/venv/Scripts/activate"),
+    ],
+)
+def test_local_windows_bash_env_prefix_converts_powershell_venv_activation(prefix, expected):
+    converted = _local_windows_bash_env_prefix(prefix)
+
+    assert converted == expected
+    assert _safe_env_prefix(converted).startswith('[ -f "')
+
+
+@pytest.mark.parametrize(
+    "prefix",
+    [
+        None,
+        "",
+        "source /home/me/venv/bin/activate",
+        "conda activate qwen35",
+        'eval "$(conda shell.bash hook)" && conda activate qwen35',
+        r"& \\server\share\venv\Scripts\Activate.ps1",
+    ],
+)
+def test_local_windows_bash_env_prefix_leaves_other_prefixes_unchanged(prefix):
+    assert _local_windows_bash_env_prefix(prefix) == prefix
+
+
+def test_local_windows_bash_env_prefix_handles_long_whitespace_input():
+    prefix = "\t" * 100_000
+
+    assert _local_windows_bash_env_prefix(prefix) == prefix
+
+
+@pytest.mark.parametrize(
+    "relative_path",
+    ["static/js/cookbookRunning.js", "static/js/cookbookDownload.js"],
+)
+def test_primary_windows_venv_emitters_quote_activation_path(relative_path):
+    source = (Path(__file__).resolve().parents[1] / relative_path).read_text(encoding="utf-8")
+
+    assert "'& ' + _psQuote(" in source
+    assert "_psQuote = shared._psQuote;" in source
+
+
+def test_windows_venv_conversion_stays_scoped_to_local_git_bash_runners():
+    source = (Path(__file__).resolve().parents[1] / "routes/cookbook_routes.py").read_text(encoding="utf-8")
+    guarded_conversion = (
+        "_local_windows_bash_env_prefix(req.env_prefix) if local_windows else req.env_prefix"
+    )
+
+    assert source.count(guarded_conversion) == 2
+
+
 def test_validate_local_dir_accepts_external_drive_paths_with_spaces():
     path = "/Volumes/T7 2TB/AI Models/llamacpp"