## Why
App-server logs can be persisted or included in submitted diagnostics, so credentials used by model providers, authentication refreshes, and attestation requests must not appear in diagnostic output.
## What changed
- Add `RedactedString`, which preserves serialization and string access while replacing debug output with `<redacted>`.
- Use it for model-provider bearer tokens, header and query values, authentication command arguments, and attestation tokens.
- Avoid logging JSON-RPC error payloads and parser or authentication errors that may echo credentials; retain safe context such as error codes and categories.
## Testing
- Add an app-server regression test that exercises provider credentials, refreshed authentication tokens, and attestation tokens, then verifies none appear in persisted SQLite or submitted diagnostic logs.
GitOrigin-RevId: 8c50408adf94d93847658b1320682cf3b637d2cc
