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/packages/harness/deerflow/persistence/repositories/feedback_repo.py

@@ -5,7 +5,6 @@ Each method acquires its own short-lived session.
 
 from __future__ import annotations
 
-import logging
 import uuid
 from datetime import UTC, datetime
 
@@ -14,8 +13,6 @@ from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
 
 from deerflow.persistence.models.feedback import FeedbackRow
 
-logger = logging.getLogger(__name__)
-
 
 class FeedbackRepository:
     def __init__(self, session_factory: async_sessionmaker[AsyncSession]) -> None:

backend/packages/harness/deerflow/persistence/repositories/run_repo.py

@@ -8,7 +8,6 @@ minutes -- we don't hold connections across long execution.
 from __future__ import annotations
 
 import json
-import logging
 from datetime import UTC, datetime
 from typing import Any
 
@@ -18,8 +17,6 @@ from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
 from deerflow.persistence.models.run import RunRow
 from deerflow.runtime.runs.store.base import RunStore
 
-logger = logging.getLogger(__name__)
-
 
 class RunRepository(RunStore):
     def __init__(self, session_factory: async_sessionmaker[AsyncSession]) -> None:

backend/packages/harness/deerflow/persistence/repositories/thread_meta_repo.py

@@ -2,7 +2,6 @@
 
 from __future__ import annotations
 
-import logging
 from datetime import UTC, datetime
 from typing import Any
 
@@ -11,8 +10,6 @@ from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
 
 from deerflow.persistence.models.thread_meta import ThreadMetaRow
 
-logger = logging.getLogger(__name__)
-
 
 class ThreadMetaRepository:
     def __init__(self, session_factory: async_sessionmaker[AsyncSession]) -> None: