When discord.auto_thread is enabled and a top-level server-channel message
should be routed to a new thread, a transient thread-create failure (e.g.
Cannot connect to host discord.com:443) returned None and _handle_message
fell through to an inline parent-channel reply — dumping a new task into a
shared channel and breaking thread-first workflows.
- _auto_create_thread retries the primary + seed-message paths once after a
750ms backoff for transient connect errors.
- _handle_message treats None as a hard failure: posts a short visible notice
in the parent channel and returns without invoking the agent. The notify
send is wrapped so a secondary connect error can't raise.
Fixes#20243
50a7dce6bd