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/README.md

@@ -15,7 +15,11 @@ instance on that host — Rust, Conan Exiles, Soulmask, Dune: Awakening.
 - [x] Connectivity prober (outbound TCP, periodic + on-demand)
 - [x] Host command channel (`ping`, `probe`, `sysinfo`)
 - [x] Graceful shutdown (cancellation token, going-offline beacon, NATS flush)
-- [ ] Phase 1: process-class game adapter (spawn/RCON/SteamCMD/files) — Rust, Conan, Soulmask
+- [x] Phase 1a: process supervision — per-instance start/stop/restart/status over
+      `{instance}.cmd` request-reply, push state events on `{instance}.status`,
+      crash detection with exit codes, live state in heartbeats
+      (integration-tested with real processes + live-NATS contract test)
+- [ ] Phase 1b: RCON trait (WebRCON rust / TCP conan+soulmask), SteamCMD, jailed file manager
 - [ ] Phase 2: Dune Docker adapter (compose lifecycle, RabbitMQ bus, Postgres admin)
 - [ ] Phase 3: signed self-update (enforced ed25519 — release gate), service install, supervisor split