## Why
Guardian Decisions retained a copied login key after the saved login changed or was removed. Queued comparisons need to respect credential changes, while runtime-bound threads must remain tied to their startup credential source.
## What changed
- Select login credentials from the thread's `ProviderAuthContext`, falling back to the supplied auth manager when no context exists.
- Resolve saved login keys before sending requests and reject queued comparisons if their credential source has changed. Pin runtime-bound credentials to the source selected at startup.
- Revalidate implicit keys before sending, rejecting missing, padded, or FedRAMP keys. Preserve explicit key overrides and the environment-key fallback.
## Testing
Extend credential lookup and queued-request tests to cover reloaded logins, runtime source pinning, rejection of stale queued comparisons, replacement-key authorization, invalid keys, and logout.
GitOrigin-RevId: 1d975613040e08c3825ba6355a166cf0fa812cad
jif
2c502d8b3d