- Introduced `RpcShutdownCoordinator` to track background tasks and manage deferred shutdowns safely.
- Guaranteed all background bash task response frames are fully written before the process exits.
- Re-checked shutdown requests automatically as each tracked background task settles.
- Latched the shutdown sequence to prevent concurrent execution from duplicate triggers.
- Updated `mock-rpc-agent` to consume stdin via an async iterator to match standard behavior.
- Added comprehensive unit tests in `rpc-input-frame.test.ts` covering background task coordination.