Previously ListenAndServe ran entirely in a goroutine, so a port-in-use
error was only logged and the launcher received nil from OnStart — leaving
the application running without an HTTP server.
Replace with net.Listen (synchronous) + srv.Serve(ln) (goroutine). A bind
failure now returns an error from OnStart, which the launcher treats as
fatal and triggers a clean shutdown immediately.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
claude
