fix(agent): release idle session locks

tests/agent/test_session_lock_lifecycle.py

@@ -0,0 +1,53 @@
+from __future__ import annotations
+
+import asyncio
+import gc
+from unittest.mock import MagicMock
+
+import pytest
+
+
+def _make_loop(loop_factory):
+    provider = MagicMock()
+    provider.get_default_model.return_value = "test-model"
+    return loop_factory(provider=provider)
+
+
+def test_idle_agent_session_locks_are_released(loop_factory):
+    loop = _make_loop(loop_factory)
+
+    for index in range(1000):
+        lock = loop._get_session_lock(f"api:temporary-{index}")
+
+    del lock
+    gc.collect()
+
+    assert len(loop._session_locks) == 0
+
+
+@pytest.mark.asyncio
+async def test_waiter_keeps_agent_session_lock_alive(loop_factory):
+    loop = _make_loop(loop_factory)
+    owner_lock = loop._get_session_lock("api:shared")
+    await owner_lock.acquire()
+    waiter_started = asyncio.Event()
+    waiter_entered = asyncio.Event()
+
+    async def wait_for_lock() -> None:
+        lock = loop._get_session_lock("api:shared")
+        waiter_started.set()
+        async with lock:
+            waiter_entered.set()
+
+    waiter = asyncio.create_task(wait_for_lock())
+    await waiter_started.wait()
+
+    assert loop._get_session_lock("api:shared") is owner_lock
+    assert not waiter_entered.is_set()
+
+    owner_lock.release()
+    await waiter
+    del owner_lock
+    gc.collect()
+
+    assert "api:shared" not in loop._session_locks