[Bug]: Executor failure right after its Task is enqueued leaves the task SUBMITTED on DatabaseTaskStore #1351

import asyncio
import collections
import tempfile
import uuid

from sqlalchemy.ext.asyncio import create_async_engine

from a2a.helpers.proto_helpers import new_task_from_user_message
from a2a.server.agent_execution import AgentExecutor
from a2a.server.context import ServerCallContext
from a2a.server.request_handlers import DefaultRequestHandler
from a2a.server.tasks.database_task_store import DatabaseTaskStore
from a2a.types.a2a_pb2 import AgentCard, Message, Part, Role, SendMessageRequest, TaskState


class FailsAfterCreatingTask(AgentExecutor):
    async def execute(self, context, event_queue):
        task = new_task_from_user_message(context.message)
        task.metadata.update({'agent_key': 'kept'})
        self.task_id = task.id
        await event_queue.enqueue_event(task)
        raise RuntimeError('model call failed')

    async def cancel(self, context, event_queue):
        pass


async def main():
    engine = create_async_engine(f'sqlite+aiosqlite:///{tempfile.mkdtemp()}/tasks.db')
    store = DatabaseTaskStore(engine)
    executor = FailsAfterCreatingTask()
    handler = DefaultRequestHandler(executor, store, AgentCard(name='repro'))
    outcomes = collections.Counter()
    for _ in range(50):
        message = Message(role=Role.ROLE_USER, message_id=str(uuid.uuid4()), parts=[Part(text='hi')])
        context = ServerCallContext()
        try:
            result = await handler.on_message_send(SendMessageRequest(message=message), context)
            client = f'returned {TaskState.Name(result.status.state)}'
        except Exception as exc:
            client = f'raised {type(exc).__name__}'
        await asyncio.sleep(0.1)
        stored = await store.get(executor.task_id, context)
        kept = 'agent_key' in stored.metadata
        outcomes[(client, TaskState.Name(stored.status.state), kept)] += 1
    for (client, state, kept), n in outcomes.most_common():
        print(f'{n:3}  {client:30} stored {state:21} metadata kept: {kept}')


asyncio.run(main())