## What changed
- Classify token-source failures by credential kind and exchange stage, with sign-in or administrator guidance that omits provider error text. Treat resource authorization failures separately from enterprise identity failures when deciding whether authentication is required.
- Add policy-bound request authority checks that return `RequestNotSent` when policy is updating or unavailable, while allowing admitted responses to finish. Support child authorities that isolate connection revocation and share response draining.
- Recheck account validity after acquiring the credential invalidation lock and check cancellation before deleting a rejected credential.
## Testing
Extend regression coverage for policy suspension during token renewal, completion of admitted requests, recovery with fresh authority, and transport retry classification. Expand provider-error tests to cover `unauthorized_client` and `invalid_client` while checking that credential text is not exposed.
GitOrigin-RevId: c0097adc35cb5fdffde1466e4bc2b5ec78114a4b