Guard session message persistence after delete (#1451)

Co-authored-by: ghreprimand <203024559+ghreprimand@users.noreply.github.com>

tests/test_session_manager_persist_guard.py

@@ -0,0 +1,52 @@
+from types import SimpleNamespace
+from unittest.mock import MagicMock
+
+from core.models import ChatMessage
+from core.session_manager import SessionManager
+import core.session_manager as SM
+
+
+def _manager_with(sessions):
+    manager = SessionManager.__new__(SessionManager)
+    manager.sessions = dict(sessions)
+    return manager
+
+
+def _session_local(parent_row):
+    db = MagicMock()
+    db.query.return_value.filter.return_value.first.return_value = parent_row
+    return MagicMock(return_value=db), db
+
+
+def test_persist_message_drops_write_when_parent_session_is_gone(monkeypatch):
+    session_local, db = _session_local(None)
+    monkeypatch.setattr(SM, "SessionLocal", session_local)
+
+    manager = _manager_with({"deleted": SimpleNamespace(history=[])})
+    message = ChatMessage("assistant", "late token")
+
+    manager._persist_message("deleted", message)
+
+    assert "deleted" not in manager.sessions
+    db.add.assert_not_called()
+    db.commit.assert_not_called()
+    db.rollback.assert_not_called()
+
+
+def test_persist_message_still_writes_when_parent_session_exists(monkeypatch):
+    parent = SimpleNamespace(message_count=0, last_accessed=None, last_message_at=None)
+    session_local, db = _session_local(parent)
+    monkeypatch.setattr(SM, "SessionLocal", session_local)
+
+    message = ChatMessage("user", "hello")
+    manager = _manager_with({"sid": SimpleNamespace(history=[message])})
+
+    manager._persist_message("sid", message)
+
+    db.add.assert_called_once()
+    db.commit.assert_called_once()
+    assert parent.message_count == 1
+    assert parent.last_accessed is not None
+    assert parent.last_message_at is not None
+    assert message.metadata["_db_id"]
+    assert message.metadata["timestamp"].endswith("Z")