## Why
Closing stdin could leave the app-server running when a remote-control client
was still connected.
## What changed
Track each connection's origin and shut down a stdio app-server when its stdio
connection closes, regardless of whether other connections remain. Report the
shutdown reason as `stdio_connection_closed`.
## Testing
Added a regression test that closes stdio while a remote-control connection is
active and verifies that the app-server exits and disconnects the remote client.
GitOrigin-RevId: 51ab14d45dfea7f40a0657a8bb167b54efaf0e48