## Why
Filtering destination variables out of a child environment can undo credential registrations. Rotating a provider token and destination must also leave older credential aliases bound to their original destinations.
## What changed
- Add `CredentialBrokerContext` to retain local destination hints for built-in and configured providers without adding them to child environments or serialized configuration. Explicit environment values, including empty values, override these fallbacks.
- Preserve registered destinations when hints are absent, reconcile fallback changes, and keep credential aliases scoped to their source identities and environments during rotation and inheritance.
- Expose provider context and source matching for trusted captured text, including configured provider context keys.
- Disable brokerage on Windows when provider environment overrides contain conflicting case-insensitive keys.
## Testing
Add regression coverage for filtered destinations, token rotation, inherited aliases, fallback updates and clearing, context redaction, trusted text matching, and non-Unicode environment values.
GitOrigin-RevId: 411790ea6339e1d8fa568049cf8160a67b134666
f45115a137