With parallel workers, threads that fetch a proxy just before escalation
can report failures after the tier has already changed — those failures
were silently counting against the new tier, immediately exhausting it
before it ever got tried (Rayobyte being skipped entirely in favour of
DataImpulse because 10 in-flight Webshare failures hit the threshold).
Fix: build a proxy_url → tier_idx reverse map at construction time and
skip the tier-level circuit breaker when the failing proxy belongs to an
already-escalated tier.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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