When Account A failed, only the first file got the fallback to Account B.
All subsequent files in the same batch still tried Account A (wasting
all retries), then skipped fallback because _failedAccounts already
had the key.
Now: before the retry loop, each job checks if its account is already
known-failed and immediately switches to the fallback account, avoiding
wasted retries on a known-bad account.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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