When Discord splits a long message at 2000 chars, _enqueue_text_event
buffers each chunk and schedules a _flush_text_batch task with a
short delay. If another chunk lands while the prior flush task is
already inside handle_message, _enqueue_text_event calls
prior_task.cancel() — and without asyncio.shield, CancelledError
propagates from the flush task into handle_message → the agent's
streaming request, aborting the response the user was waiting on.
Reproducer: user sends a 3000-char prompt (split by Discord into 2
messages). Chunk 1 lands, flush delay starts, chunk 2 lands during
the brief window when chunk 1's flush has already committed to
handle_message. Agent's current streaming response is cancelled
with CancelledError, user sees a truncated or missing reply.
Fix (gateway/platforms/discord.py):
- Wrap the handle_message call in asyncio.shield so the inner
dispatch is protected from the outer task's cancel.
- Add an except asyncio.CancelledError clause so the outer task
still exits cleanly when cancel lands during the sleep window
(before the pop) — semantics for that path are unchanged.
The new flush task spawned by the follow-up chunk still handles its
own batch via the normal pending-message / active-session machinery
in base.py, so follow-ups are not lost.
Tests: tests/gateway/test_text_batching.py —
test_shield_protects_handle_message_from_cancel. Tracks a distinct
first_handle_cancelled event so the assertion fails cleanly when the
shield is missing (verified by stashing the fix and re-running).
Live E2E on the live-loaded DiscordAdapter:
first_handle_cancelled: False (shield worked)
first_handle_completed: True (handle_message ran to completion)
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