feat(host-agent): Phase 1a process supervision — instance start/stop/restart/status + push state events

Per-instance ProcessSupervisor: tokio child spawn with proper arg list
(fixes Go's naive space-splitting), graceful SIGTERM with 30s budget
then force kill, monitor task classifying ordered-stop vs crash (exit
code captured), watch-channel state observable everywhere. Instance cmd
channel live on corrosion.{license}.{instance}.cmd (start/stop/restart/
status) with state events pushed on {instance}.status (keep-latest
semantics, documented). Heartbeats now carry live process state +
uptime per instance. Crate restructured lib+bin for integration tests.

Verified: 5 integration tests with real OS processes (lifecycle, crash
exit-code, restart recovery, unmanaged rejection, clean spawn failure)
+ live-NATS contract test (request-reply roundtrips, double-start
rejection, push events, heartbeat state) — all green.

Known limitation (documented): no PID adoption yet — agent restart
orphans a running game process to 'stopped' until panel restart.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

corrosion-host-agent/src/main.rs

@@ -4,14 +4,9 @@
 //! connectivity prober, host command channel. Process control, file ops, and
 //! game adapters arrive in Phase 1+ (see PROTOCOL.md).
 
-mod agent;
-mod bus;
-mod config;
-mod hostcmd;
-mod prober;
-mod subjects;
-mod telemetry;
-mod version;
+use corrosion_host_agent::{
+    agent, bus, config, hostcmd, instancecmd, prober, process, subjects, telemetry, version,
+};
 
 use anyhow::{Context, Result};
 use clap::{Parser, Subcommand};
@@ -96,11 +91,18 @@ async fn run(settings: config::Settings) -> Result<()> {
 
     let nats = bus::connect(&settings).await?;
 
+    let supervisors = settings
+        .instances
+        .iter()
+        .map(|inst| (inst.id.clone(), process::ProcessSupervisor::new(inst)))
+        .collect();
+
     let agent = Arc::new(Agent {
         cfg: settings,
         nats,
         started: Instant::now(),
         last_probe: RwLock::new(None),
+        supervisors,
         shutdown: CancellationToken::new(),
     });
 
@@ -115,6 +117,21 @@ async fn run(settings: config::Settings) -> Result<()> {
             }
         }));
     }
+    for sup in agent.supervisors.values() {
+        {
+            let agent = agent.clone();
+            let sup = sup.clone();
+            handles.push(tokio::spawn(async move {
+                if let Err(e) = instancecmd::run(agent, sup).await {
+                    tracing::error!("instance command handler failed: {e:#}");
+                }
+            }));
+        }
+        handles.push(tokio::spawn(instancecmd::publish_state_changes(
+            agent.clone(),
+            sup.clone(),
+        )));
+    }
 
     wait_for_shutdown_signal().await;
     tracing::info!("shutdown signal received");