hermes - 💡(How to fix) Fix Race condition in kanban _migrate_add_optional_columns on gateway startup

Bug

On gateway startup, the kanban dispatcher crashes with:

sqlite3.OperationalError: duplicate column name: consecutive_failures

Root Cause

Two async tasks are created concurrently in the gateway (gateway/run.py):

• Line 3335: asyncio.create_task(self._kanban_notifier_watcher())
• Line 3341: asyncio.create_task(self._kanban_dispatcher_watcher())

Both watchers call _kb.connect(board=slug) → _migrate_add_optional_columns(conn) via asyncio.to_thread().

The _INITIALIZED_PATHS set (module-level, kanban_db.py:~917) is used as a cache to skip re-initialization, but it is not thread-safe. When both threads race on the first tick:

1. Thread A checks needs_init = resolved not in _INITIALIZED_PATHS → True
2. Thread B checks needs_init = resolved not in _INITIALIZED_PATHS → True (set not yet updated by A)
3. Both threads run _migrate_add_optional_columns()
4. Both read cols via PRAGMA table_info(tasks) — neither sees consecutive_failures yet
5. Thread A succeeds with ALTER TABLE tasks ADD COLUMN consecutive_failures ...
6. Thread B crashes with duplicate column name: consecutive_failures

The error is caught at the outer exception handler (gateway/run.py:3889) so the gateway keeps running, but the kanban dispatcher tick is lost.

Reproduction

Start the gateway with a fresh or existing kanban.db that already has consecutive_failures in the schema (i.e., after a previous successful migration). The race window is tight but triggers reliably on startup when both watchers hit their first tick close together.

Environment

• Hermes v0.6+ (323 commits behind → updated to latest main as of bbff2f634)
• Python 3.14, SQLite 3.x
• Linux (NixOS)

Suggested Fix

Either:

1. Quick fix: Wrap each ALTER TABLE in _migrate_add_optional_columns with try/except sqlite3.OperationalError catching only duplicate column errors. Other errors still propagate.
2. Proper fix: Use a threading.Lock around the needs_init check + migration block in connect(), or use CREATE TABLE IF NOT EXISTS style guards.

I can submit a PR for option 1 or 2 if desired. Thanks!