d84a54e579
- 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.