reindexWorkspace isolated every per-page failure, so an invalid/missing
API key (401 "User not found") made all pages fail identically while the
batch kept issuing hundreds of doomed requests against the provider.
Add isFatalProviderError() (401/403 auth, 402 billing) and abort the
whole batch on such errors; 429 rate-limit and embedding timeouts stay
per-page isolated. Adds unit tests for the predicate and a regression
test for the abort/iterate control flow.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>