The typing indicator loop (send_typing) ran every 8s and died on any
exception, including Discord 429 rate limits. Once a 429 killed the
loop, the indicator never restarted — and the raw exception bounce
could cascade into broader gateway instability.
Changes:
- Bump sleep interval from 8s to 12s (typing light lasts ~10s)
- On 429: extract retry_after, log a warning, sleep the backoff,
and continue the loop
- On non-rate-limit errors: log debug and return (unchanged
behaviour)
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