refactor: simplify task and history services

Remove retired query paths and repository compatibility branches, and share task test fixtures.
Cancel pending questions and resolve their notifications when recovering expired runs.

tests/unit/test_agent_messages.py

@@ -44,6 +44,12 @@ class Repository:
     async def get_task(self, task_id):
         return {"task_type": "event_investigation"} if task_id == str(self.task_id) else None
 
+    async def list_questions(self, task_id):
+        return []
+
+    async def pending_calculation_jobs(self, task_id, run_id, execution_request_id):
+        return []
+
     async def get_message(self, message_id):
         return self.messages.get(message_id)