Replace watch::Receiver<ServerState> on SupervisorHandle with watch::Receiver<Status>,
a richer snapshot type that carries pid, port, uptime_secs, restart_count and last_exit.
SupervisorTask maintains current_pid and publishes a fresh Status on every state
transition; handlers.rs reads the full Status so list/status no longer return
zeroed/None fields.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
One async task per managed server owns all state transitions via a
tokio::select! loop over cmd_rx and wait_child. Includes RealSpawner
and a smoke test covering the Start → Running → exit → Stopped →
Shutdown happy path.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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