## What changed
Add `RuntimeAuthManager` to share one registered runtime per credential source and return request-scoped `RuntimeAuth` values that pair the runtime with its credentials and HTTP client factory.
- Preserve registration keys and idempotency IDs across retryable failures and refreshes that retain the credential source.
- Replace the runtime when the credential source changes, preserve existing request snapshots, and reject late registration responses for a previous source.
- Use bounded credential recovery for registration `401` responses and cache `403` denials until the credential source changes.
- Expose authenticated actor and agent host information on `RuntimeAgentInstance`.
## Testing
Add tests for concurrent registration sharing, retry identity preservation, network policy recovery, credential refresh and replacement, bounded recovery, cached denials, and credential changes during registration.
GitOrigin-RevId: ea1e6e10a5939e8c3f7c0c317ccf8a83522c635f
cooper-oai
091008729d