fix(stabilization): harden attachment lifecycle and agent guard signals (#5420)

* fix: harden stabilization attachment and agent guards

* fix(uploads): preserve durable references during cleanup

* fix(uploads): close cleanup and compaction races

routes/history/history_routes.py

@@ -10,7 +10,9 @@ from fastapi import APIRouter, Request, HTTPException
 
 from core.models import ChatMessage
 from core.database import SessionLocal, ChatMessage as DbChatMessage, Session as DbSession
+from src.auth_helpers import effective_user
 from src.topic_analyzer import analyze_topics
+from src.upload_handler import reserve_message_upload_references
 from routes.session_routes import (
     _message_role,
     _message_text,
@@ -98,9 +100,29 @@ def _merge_continue_rows_to_delete(db_messages, db1, db2):
     return to_delete
 
 
-def setup_history_routes(session_manager) -> APIRouter:
+def setup_history_routes(session_manager, upload_handler=None) -> APIRouter:
     router = APIRouter(tags=["history"])
 
+    def _reserve_message_uploads(
+        request: Request,
+        content: Any,
+        metadata: Any = None,
+    ) -> None:
+        try:
+            missing_id = reserve_message_upload_references(
+                upload_handler,
+                effective_user(request),
+                content,
+                metadata,
+            )
+        except (TypeError, ValueError) as exc:
+            raise HTTPException(400, "Invalid message attachment metadata") from exc
+        if missing_id:
+            raise HTTPException(
+                409,
+                f"Referenced upload is no longer available: {missing_id}",
+            )
+
     def _db_history_entry(m: DbChatMessage) -> Dict[str, Any]:
         entry = {"role": m.role, "content": _history_display_content(m.content)}
         meta = {}
@@ -251,7 +273,9 @@ def setup_history_routes(session_manager) -> APIRouter:
             content = body.get("content", "")
             if not content:
                 raise HTTPException(400, "content is required")
-            msg = ChatMessage(role=role, content=content, metadata=body.get("metadata"))
+            metadata = body.get("metadata")
+            _reserve_message_uploads(request, content, metadata)
+            msg = ChatMessage(role=role, content=content, metadata=metadata)
             session_manager.add_message(session_id, msg)
             return {"status": "ok"}
         except KeyError:
@@ -331,6 +355,8 @@ def setup_history_routes(session_manager) -> APIRouter:
             if not msg_id or content is None:
                 raise HTTPException(400, "msg_id and content are required")
 
+            _reserve_message_uploads(request, content)
+
             session = session_manager.get_session(session_id)
             db = SessionLocal()
             try: