fix(harness): ship coherent vendor harness cluster

Rebuild PR C to ship the vendor/photocraft harness as a coherent unit
(vendor implementation + vendor tests) instead of a per-file ahead/behind
mix that produced broken imports and 6+ test failures.

- Flip 36 harness impl/route/test files back to vendor (the per-file
  line-set policy misclassified user-rewritten files as 'behind').
- Flip core/models.py + src/tool_approval_scopes.py to vendor: vendor's
  harness (authority.py, turn_contract.py, clean_agent_preview.py) depends
  on vendor's older approval-scope API; upstream added
  CHAT_SESSION_APPROVAL_SIGNATURE_FIELD that vendor's core/models.py lacks.
- Add src/shutdown.py (new vendor infra) required by routes/chat_routes.py.
- Keep src/agent_tools/__init__.py at upstream (editor_tools registration
  lives in PR B).

Upstream-only security divergence preserved in C_upstream_delta.patch and
flagged for integration-time reconciliation.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

core/models.py

@@ -11,8 +11,6 @@ from typing import Dict, List, Any, Optional, TYPE_CHECKING
 from src.tool_approval_scopes import (
     CHAT_SESSION_APPROVAL_CONTEXT_MARKER,
     CHAT_SESSION_APPROVAL_DECISION,
-    CHAT_SESSION_APPROVAL_SIGNATURE_FIELD,
-    verify_chat_session_grant,
 )
 
 if TYPE_CHECKING:
@@ -62,14 +60,6 @@ def _history_grants_chat_session_approval(
                 ask_user.get("kind") == "tool_approval"
                 and ask_user.get("resolved") == CHAT_SESSION_APPROVAL_DECISION
                 and str(ask_user.get("session_id") or "") == expected_session
-                # Shape proves nothing here: routes that accept a
-                # caller-supplied metadata blob write into this same history.
-                and verify_chat_session_grant(
-                    ask_user.get(CHAT_SESSION_APPROVAL_SIGNATURE_FIELD),
-                    expected_session,
-                    ask_user.get("approval_id"),
-                    CHAT_SESSION_APPROVAL_DECISION,
-                )
             ):
                 return True
     return False