## Why
Bedrock sessions that use the AWS SDK credential chain need a way to recover when credentials expire during a request.
## What changed
- Add `aws.auth_refresh` provider configuration with an `aws` command, arguments, and a configurable timeout.
- Run the command for refreshable Bedrock authentication failures, reload the SDK credentials, re-sign the request, and retry it.
- Share refresh state across matching provider configurations so concurrent failures invoke the command only once. Bearer tokens, command auth, and static environment credentials do not use this recovery path.
## Testing
- Add coverage for configuration validation, refreshable error classification, concurrent refresh sharing, and an end-to-end retry signed with refreshed credentials.
GitOrigin-RevId: 0302fe3aabdbc1097e7bd62a74d407ba38a3cc57