Wrapping the coroutine in `asyncio.wait_for` outside `asyncio.run` left the
running-loop fallback (which closes the unstarted coroutine and retries in a
thread) with a never-awaited wait_for wrapper and an unbounded inner send.
Awaiting `wait_for` inside `_send` bounds every runner of the coroutine.
The invariant tests now drive the production entry point `_deliver_result`
with no live adapters (the standalone lane) instead of `_standalone_send`
directly, and the user-visible knob `cron.standalone_send_timeout_seconds`
is documented (#115469).
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