A dead background event loop tears the loop's default executor down, and
after that every inbound message was dropped inside the dedup gate with a
RuntimeError out of asyncio.to_thread — the adapter went permanently deaf
while the gateway process, websocket and service all stayed healthy.
#10849 already moved the outbound SDK calls onto an adapter-owned,
self-healing pool; this gives the inbound dedup-state flush the same
treatment, so a default-executor teardown can no longer wedge message
intake.
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