feat(host-agent): Phase 2 — Dune docker-compose adapter via Supervisor trait

Introduce a Supervisor trait (async-trait) so the agent manages games with
different models behind one wire contract. ProcessSupervisor (spawned process:
rust/conan/soulmask) and the new DockerComposeSupervisor (dune) both impl it;
Agent.supervisors is now HashMap<String, Arc<dyn Supervisor>> and instancecmd
dispatch is game-agnostic — start/stop/restart/status identical across games,
selected by a per-game factory in main. InstanceState moved to the shared
supervisor module.

DockerComposeSupervisor drives docker-compose up-d / stop / restart against
the instance's compose project, with -f/-p/single-service support and a
configurable compose binary. New [instance.docker_compose] config block.
First cut = lifecycle + cached state; container crash-detection + restart
adoption deferred to Phase 3b (reconcilable with a compose ps probe).

Trait choice (dyn over enum) per Commander: scales to future planes (kubectl,
AMP/podman, SSH) as new struct+impl, no central match.

56 tests green (6 new docker-compose mock-binary tests + 5 refactored process
tests), zero warnings. Live verification pending a real Dune stack.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -4,6 +4,17 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+### Added (Host-agent Phase 2 — Dune docker-compose adapter — 2026-06-12)
+
+**`Supervisor` trait abstraction (`corrosion-host-agent`):**
+- Introduced `trait Supervisor` (via `async-trait`, the battle-tested ecosystem standard) so the agent can manage games with fundamentally different models behind one wire contract. `ProcessSupervisor` (spawned OS process — Rust/Conan/Soulmask) and the new `DockerComposeSupervisor` (Dune) both implement it; `Agent.supervisors` is now `HashMap<String, Arc<dyn Supervisor>>` and the instance command dispatch (`instancecmd::dispatch`) is fully game-agnostic — `start`/`stop`/`restart`/`status` are identical across games. A per-game factory in `main` selects the impl. `InstanceState` moved to the shared `supervisor` module.
+- **Architecture call** (per Commander): chose the `dyn` trait over a zero-dependency enum because the Dune references point at *several* future management planes (kubectl, AMP/podman, SSH) — a trait makes each new plane "new struct + impl," no central match to edit.
+
+**`DockerComposeSupervisor` (Dune: Awakening):**
+- Drives `docker compose up -d` / `stop` / `restart` against the instance's compose project (a "battlegroup"), with `-f`/`-p`/single-service support and a configurable compose binary (`docker compose` default, `docker-compose` legacy). New `[instance.docker_compose]` config block (file/project/service/command, all optional). `steam_update` already rejected for Dune (Docker images, no SteamCMD).
+- **Scope (first cut):** lifecycle + cached state. Deferred to Phase 3b (with process PID adoption): container crash-detection and state adoption on agent restart (both reconcilable with a `docker compose ps` probe).
+- Verified: 6 new docker-compose tests (mock `docker` binary asserting exact invocations + state transitions + failure paths) + the 5 refactored process-supervisor tests; full agent suite 56 tests green, zero warnings. Live verification against a real Dune stack pending the Commander standing one up.
+
 ### Changed (Fleet-driven active game + signed-update CI fix — 2026-06-12)
 
 **Frontend — active game follows the deployed fleet:**