## What changed
- Add typed helpers for initialized app-server instances, JSON-RPC requests,
responses, notifications, and thread startup.
- Add a composable `MockResponsesConfig` builder while preserving the existing
mock config writers.
- Migrate the app-server integration suite to the shared helpers, removing
repeated request ID management, deserialization, initialization, and config
assembly.
## Testing
- Add unit coverage for composing mock provider, feature, and extra config, and
for compatibility of the existing mock config writer.
GitOrigin-RevId: 62da177c1d6e8299400de64bd6766567bf1ba3d8
