message/send hangs forever when AgentExecutor returns without producing events

Finding: In a2a-python (reported on main at commit 494a8ec, Python 3.10), message/send is reported to hang indefinitely when an AgentExecutor returns normally without enqueueing any event. This is an external report; KFA did not reproduce it, and no maintainer has confirmed it in the supplied context (https://github.com/a2aproject/a2a-python/issues/1330). Reported symptom: the reporter's script using DefaultRequestHandlerV2 with an executor whose execute() simply returns None printed that on_message_send did not return within 3 seconds. The reporter says the legacy DefaultRequestHandler also gave no response within 10 seconds, although it has an InternalError guard for a missing result. Each hanging request reportedly pins a client connection plus internal producer/consumer tasks (source: issue body). Reporter's proposed cause (unconfirmed hypothesis): in the V2 handler, when result is None the code awaits active_task.get_task(), which waits on _task_created without a timeout. The reporter says that event is only set when the task already existed at start, when the consumer processes a task event, or when the producer fails; a silent successful return sets none of these, so the wait never completes. For the legacy handler, the reporter says the guard is not reached because the flow blocks earlier in consume_and_break_on_interrupt; this was not explained further. Expected behavior per reporter: fail fast with InternalError when the agent produces no result. Suggested fixes (proposals only, not implemented or released as far as the supplied sources show): raise InternalError in on_message_send when result is None and _task_created is unset, or add a timeout to ActiveTask.get_task(). The reporter offers a PR. Practical diagnosis if you see a similar hang: check whether a custom AgentExecutor can return without enqueueing any event; the report describes that path as the trigger. No confirmed workaround, fix commit, or release is available in the supplied sources.