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/migrations/env.py

@@ -8,6 +8,7 @@ have their own schema lifecycle and must not be touched by Alembic.
 from __future__ import annotations
 
 import asyncio
+import logging
 from logging.config import fileConfig
 
 from alembic import context
@@ -17,9 +18,13 @@ from deerflow.persistence.base import Base
 
 # Import all models so metadata is populated.
 try:
-    import deerflow.persistence.models  # noqa: F401
+    import deerflow.persistence.models  # noqa: F401 — register ORM models with Base.metadata
 except ImportError:
-    pass
+    # Models not available — migration will work with existing metadata only.
+    logging.getLogger(__name__).warning(
+        "Could not import deerflow.persistence.models; "
+        "Alembic may not detect all tables"
+    )
 
 config = context.config
 if config.config_file_name is not None: