fix: history DB fallback returned hidden (compaction) messages to the client (#1726)

GET /api/history/{session_id} skips messages whose metadata has `hidden` (e.g.
compaction summaries kept for AI context, not shown to the user) on the
in-memory path. The DB fallback — used when the in-memory history is empty,
e.g. after a restart — built the response from every stored row with no such
filter, so hidden messages leaked to the client on DB-served sessions.

Filter `hidden` out of the response on the DB path too. The rebuilt in-memory
session.history still includes them, so AI context (the compaction summaries)
is preserved.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

routes/history_routes.py

@@ -58,7 +58,7 @@ def setup_history_routes(session_manager) -> APIRouter:
                     .all()
                 )
                 import json as _json
-                history_dict = []
+                db_history = []
                 for m in db_messages:
                     entry = {"role": m.role, "content": m.content}
                     meta = {}
@@ -71,12 +71,19 @@ def setup_history_routes(session_manager) -> APIRouter:
                         meta["timestamp"] = m.timestamp.isoformat() + "Z"
                     if meta:
                         entry["metadata"] = meta
-                    history_dict.append(entry)
-                if history_dict:
+                    db_history.append(entry)
+                if db_history:
+                    # Rebuild in-memory history from the full set so hidden
+                    # messages (e.g. compaction summaries) are kept for AI context.
                     session.history = [
                         ChatMessage(role=m["role"], content=m["content"], metadata=m.get("metadata"))
-                        for m in history_dict
+                        for m in db_history
                     ]
+                # Response excludes hidden messages, matching the in-memory path.
+                history_dict = [
+                    m for m in db_history
+                    if not (m.get("metadata") or {}).get("hidden")
+                ]
             except Exception as e:
                 logger.error(f"DB fallback failed for {session_id}: {e}")
             finally: