BiliBili API returns HTTP 412 (Precondition Failed) as a non-standard rate limit response. The application would retry indefinitely on this error instead of stopping with a clear message.

Changes

• Added RateLimitError exception (commons/utils.py)

  • Signals rate limit exceeded to stop retry loop

• Enhanced exception handling (downmux/orchestrator.py)

  • Detects HTTP 412 + "Precondition Failed" in error messages/tracebacks
  • Pattern matches "HTTP Error 412:" or "HTTPError 412:" (with colon/space) to avoid false positives
  • Displays user message and raises RateLimitError to exit cleanly

Behavior

When rate limited, users see:

ERROR  Rate limit detected (HTTP 412: Precondition Failed)
ERROR  It appears you've made too many requests in a short period. Please take a break and try again after at least an hour.

Application exits instead of retrying.

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