A model that intermittently lacks an image endpoint on kilo returns 404
"No endpoints found that support image input". The kilo handler counted every
exception (that 404, a 400 for an undecodable image, a 429) toward the
three-strike cooldown, so a few request-scoped errors disabled kilo-spora for
ALL traffic for 5 minutes — during which a high-rate client piled up thousands
of 503 "in failure cooldown" rejections.

Add a shared classifier in providers/base.py: is_request_scoped_error /
is_request_scoped_status / extract_http_status treat 400/404/413/415/422/429
(and the wrapped streaming-error message form) as request-scoped — about the
specific request, not provider health. Genuine faults (5xx, timeouts, network)
still count.

Wire it into both places that record failures:
- KiloProviderHandler.handle_request and _handle_streaming_request skip
  record_failure() for request-scoped errors (429 still routes through
  handle_429_error for adaptive backoff).
- handlers._should_record_failure excludes them for every provider.

The error still propagates to the caller; it just no longer disables the whole
provider. Only a genuinely unhealthy provider now enters the cooldown.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>