fix(sqlite-store): add periodic cleanup timer for connection pool

Implement background timer to proactively clean stale connections
every 5 minutes, preventing indefinite accumulation.

Solution-ID: SOL-1735392000002
Issue-ID: ISS-1766921318981-3
Task-ID: T1

codex-lens/tests/test_sqlite_store.py

@@ -0,0 +1,61 @@
+"""Tests for SQLiteStore connection pool behavior."""
+
+from __future__ import annotations
+
+import threading
+import time
+from pathlib import Path
+
+import pytest
+
+from codexlens.storage.sqlite_store import SQLiteStore
+
+
+def test_periodic_cleanup(monkeypatch: pytest.MonkeyPatch, tmp_path: Path) -> None:
+    """Periodic timer should proactively clean up stale thread connections."""
+    monkeypatch.setattr(SQLiteStore, "CLEANUP_INTERVAL", 0.2)
+
+    store = SQLiteStore(tmp_path / "periodic_cleanup.db")
+    store.initialize()
+
+    cleanup_called = threading.Event()
+    original_cleanup = store._cleanup_stale_connections
+
+    def wrapped_cleanup() -> None:
+        cleanup_called.set()
+        original_cleanup()
+
+    monkeypatch.setattr(store, "_cleanup_stale_connections", wrapped_cleanup)
+
+    created: list[int] = []
+    lock = threading.Lock()
+    main_tid = threading.get_ident()
+
+    def worker() -> None:
+        store._get_connection()
+        with lock:
+            created.append(threading.get_ident())
+
+    try:
+        threads = [threading.Thread(target=worker) for _ in range(10)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+
+        # Ensure we created thread-local connections without reaching MAX_POOL_SIZE.
+        assert len(store._pool) >= 2
+        assert all(tid in store._pool for tid in created)
+
+        # Wait for periodic cleanup to run and prune dead thread connections.
+        assert cleanup_called.wait(timeout=3)
+        deadline = time.time() + 3
+        while time.time() < deadline and any(tid in store._pool for tid in created):
+            time.sleep(0.05)
+
+        assert all(tid not in store._pool for tid in created)
+        assert set(store._pool.keys()).issubset({main_tid})
+    finally:
+        store.close()
+
+