fix(chat): audit fixes — retention, rag_project_id, cleanup scheduler, tool rounds

- cleanup_old_conversations now excludes briefing conversations (was
  silently deleting briefing history after the retention window)
- list_conversations response now includes rag_project_id, matching the
  shape returned by the single-conversation GET endpoint
- create_conversation_from_article: removed duplicate async_session import
  (_session2 was a copy of the same import); consolidated into one
- MAX_TOOL_ROUNDS fixed from 5→6 to match the actual range(6) loop;
  loop updated to range(MAX_TOOL_ROUNDS) so the constant is accurate
- Chat retention cleanup moved from per-request (every GET /conversations)
  to a daily scheduled job in event_scheduler.py; route no longer runs
  a DB write on every read

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/fabledassistant/services/event_scheduler.py

@@ -1,7 +1,8 @@
-"""Scheduler jobs for calendar events.
+"""Scheduler jobs for background maintenance tasks.
 
-- Reminder notifications: checks every 5 minutes for due reminders.
+- Reminder notifications: checks every 5 minutes for due event reminders.
 - CalDAV pull sync: runs every hour for all users with CalDAV configured.
+- Chat retention cleanup: runs daily, deleting old conversations per user setting.
 
 Uses the same BackgroundScheduler pattern as briefing_scheduler.py.
 """
@@ -97,6 +98,44 @@ def _run_caldav_sync_threadsafe(loop: asyncio.AbstractEventLoop) -> None:
     asyncio.run_coroutine_threadsafe(_run_caldav_sync(), loop)
 
 
+# ---------------------------------------------------------------------------
+# Chat retention cleanup job
+# ---------------------------------------------------------------------------
+
+async def _run_chat_retention_cleanup() -> None:
+    """Delete old conversations for all users according to their retention setting."""
+    from sqlalchemy import select as sa_select  # noqa: PLC0415
+
+    from fabledassistant.models.user import User  # noqa: PLC0415
+    from fabledassistant.services.chat import cleanup_old_conversations  # noqa: PLC0415
+    from fabledassistant.services.settings import get_setting  # noqa: PLC0415
+
+    async with async_session() as session:
+        result = await session.execute(sa_select(User.id))
+        user_ids = [row[0] for row in result.all()]
+
+    total_deleted = 0
+    for user_id in user_ids:
+        try:
+            retention_str = await get_setting(user_id, "chat_retention_days", "90")
+            try:
+                retention_days = int(retention_str)
+            except (ValueError, TypeError):
+                retention_days = 90
+            if retention_days > 0:
+                deleted = await cleanup_old_conversations(user_id, retention_days)
+                total_deleted += deleted
+        except Exception:
+            logger.warning("Chat retention cleanup failed for user %d", user_id, exc_info=True)
+
+    if total_deleted:
+        logger.info("Chat retention cleanup: deleted %d conversation(s)", total_deleted)
+
+
+def _run_chat_retention_threadsafe(loop: asyncio.AbstractEventLoop) -> None:
+    asyncio.run_coroutine_threadsafe(_run_chat_retention_cleanup(), loop)
+
+
 # ---------------------------------------------------------------------------
 # Lifecycle
 # ---------------------------------------------------------------------------
@@ -126,8 +165,17 @@ def start_event_scheduler(loop: asyncio.AbstractEventLoop) -> None:
         replace_existing=True,
     )
 
+    # Chat retention cleanup once per day
+    _scheduler.add_job(
+        _run_chat_retention_threadsafe,
+        trigger=IntervalTrigger(hours=24),
+        args=[loop],
+        id="chat_retention_cleanup",
+        replace_existing=True,
+    )
+
     _scheduler.start()
-    logger.info("Event scheduler started (reminders every 5m, CalDAV sync every 1h)")
+    logger.info("Event scheduler started (reminders every 5m, CalDAV sync every 1h, chat cleanup every 24h)")
 
 
 def stop_event_scheduler() -> None: