fix(sqlite-store): improve thread tracking in connection cleanup

Add fallback validation to detect dead threads missed by
threading.enumerate(), ensuring all stale connections are cleaned.

Solution-ID: SOL-1735392000002
Issue-ID: ISS-1766921318981-3
Task-ID: T2

codex-lens/tests/test_sqlite_store.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import logging
 import threading
 import time
 from pathlib import Path
@@ -59,3 +60,57 @@ def test_periodic_cleanup(monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> No
         store.close()
 
 
+def test_cleanup_robustness(
+    monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture, tmp_path: Path
+) -> None:
+    """Cleanup should handle dead threads, idle timeouts, and invalid connections."""
+    monkeypatch.setattr(SQLiteStore, "CLEANUP_INTERVAL", 0)
+    caplog.set_level(logging.DEBUG, logger="codexlens.storage.sqlite_store")
+
+    store = SQLiteStore(tmp_path / "cleanup_robustness.db")
+    store.initialize()
+
+    try:
+        # Invalid connection: active thread but pooled connection is already closed.
+        conn = store._get_connection()
+        conn.close()
+        with store._pool_lock:
+            store._pool[threading.get_ident()] = (conn, time.time())
+            store._cleanup_stale_connections()
+
+        assert "invalid_connection" in caplog.text
+        assert threading.get_ident() not in store._pool
+
+        # Ensure next access recreates a working connection after cleanup.
+        fresh_conn = store._get_connection()
+        assert fresh_conn is not conn
+
+        # Idle timeout cleanup should be logged distinctly.
+        with store._pool_lock:
+            store._pool[threading.get_ident()] = (fresh_conn, time.time() - store.IDLE_TIMEOUT - 1)
+            store._cleanup_stale_connections()
+
+        assert "idle_timeout" in caplog.text
+        assert threading.get_ident() not in store._pool
+
+        # Dead thread cleanup should be logged distinctly.
+        created: list[int] = []
+
+        def worker() -> None:
+            store._get_connection()
+            created.append(threading.get_ident())
+
+        t = threading.Thread(target=worker)
+        t.start()
+        t.join()
+
+        dead_tid = created[0]
+        assert dead_tid in store._pool
+        with store._pool_lock:
+            store._cleanup_stale_connections()
+
+        assert "dead_thread" in caplog.text
+        assert dead_tid not in store._pool
+    finally:
+        store.close()
+