fix(persistence): address 22 review comments from CodeQL, Copilot, and Code Quality

Bug fixes:
- Sanitize log params to prevent log injection (CodeQL)
- Reset threads_meta.status to idle/error when run completes
- Attach messages only to latest checkpoint in /history response
- Write threads_meta on POST /threads so new threads appear in search

Lint fixes:
- Remove unused imports (journal.py, migrations/env.py, test_converters.py)
- Convert lambda to named function (engine.py, Ruff E731)
- Remove unused logger definitions in repos (Ruff F841)
- Add logging to JSONL decode errors and empty except blocks
- Separate assert side-effects in tests (CodeQL)
- Remove unused local variables in tests (Ruff F841)
- Fix max_trace_content truncation to use byte length, not char length

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/gateway/services.py

@@ -18,6 +18,7 @@ from fastapi import HTTPException, Request
 from langchain_core.messages import HumanMessage
 
 from app.gateway.deps import get_checkpointer, get_run_event_store, get_run_manager, get_run_store, get_store, get_stream_bridge, get_thread_meta_repo
+from app.gateway.routers.threads import _sanitize_log_param
 from deerflow.runtime import (
     END_SENTINEL,
     HEARTBEAT_SENTINEL,
@@ -184,7 +185,7 @@ async def _upsert_thread_in_store(store, thread_id: str, metadata: dict | None)
     try:
         await _store_upsert(store, thread_id, metadata=metadata)
     except Exception:
-        logger.warning("Failed to upsert thread %s in store (non-fatal)", thread_id)
+        logger.warning("Failed to upsert thread %s in store (non-fatal)", _sanitize_log_param(thread_id))
 
 
 async def _sync_thread_title_after_run(
@@ -312,7 +313,7 @@ async def start_run(
             else:
                 await thread_meta_repo.update_status(thread_id, "running")
         except Exception:
-            logger.warning("Failed to upsert thread_meta for %s (non-fatal)", thread_id)
+            logger.warning("Failed to upsert thread_meta for %s (non-fatal)", _sanitize_log_param(thread_id))
 
     agent_factory = resolve_agent_factory(body.assistant_id)
     graph_input = normalize_input(body.input)