The platform callback verifier can do blocking network I/O (e.g. the
google-chat adapter fetches Google signing certs on a cache miss), which
would stall the event loop if called inline. Run sync verifiers via
asyncio.to_thread (await coroutine verifiers directly), and treat a
crashing verifier as a 401 rather than a 500 through the dispatch path —
a broken verifier must never admit an event.
Teknium
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