enhance: use weak session lock registry

src/opencode_a2a/execution/session_manager.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import asyncio
+import weakref
 
 from ..invocation import call_with_supported_kwargs
 from ..server.state_store import MemorySessionStateRepository, SessionStateRepository
@@ -24,7 +25,9 @@ def __init__(
         )
         self._lock = asyncio.Lock()
         self._inflight_session_creates: dict[tuple[str, str], asyncio.Task[str]] = {}
-        self._session_locks: dict[str, asyncio.Lock] = {}
+        self._session_locks: weakref.WeakValueDictionary[str, asyncio.Lock] = (
+            weakref.WeakValueDictionary()
+        )
 
     async def get_or_create_session(
         self,

tests/execution/test_session_lock_lifecycle.py

@@ -0,0 +1,33 @@
+import gc
+import weakref
+from unittest.mock import AsyncMock
+
+import pytest
+
+from opencode_a2a.execution.session_manager import SessionManager
+from opencode_a2a.opencode_upstream_client import OpencodeUpstreamClient
+
+
+@pytest.mark.asyncio
+async def test_session_manager_reuses_live_lock_for_same_session() -> None:
+    manager = SessionManager(client=AsyncMock(spec=OpencodeUpstreamClient))
+
+    lock1 = await manager.get_session_lock("session-1")
+    lock2 = await manager.get_session_lock("session-1")
+
+    assert lock1 is lock2
+
+
+@pytest.mark.asyncio
+async def test_session_manager_does_not_strongly_retain_idle_locks() -> None:
+    manager = SessionManager(client=AsyncMock(spec=OpencodeUpstreamClient))
+
+    lock = await manager.get_session_lock("session-1")
+    lock_ref = weakref.ref(lock)
+    assert "session-1" in manager._session_locks
+
+    del lock
+    gc.collect()
+
+    assert lock_ref() is None
+    assert "session-1" not in manager._session_locks