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>

corrosion-host-agent/tests/docker_compose.rs

@@ -0,0 +1,156 @@
+//! DockerComposeSupervisor tests. A fake `docker` script records the exact
+//! arguments it was invoked with and returns a controllable exit code, so we
+//! assert the compose invocations + state transitions with no real Docker
+//! daemon — the same mock-the-external-binary approach the steamcmd tests use.
+#![cfg(unix)]
+
+use std::os::unix::fs::PermissionsExt;
+use std::path::{Path, PathBuf};
+
+use corrosion_host_agent::config::InstanceConfig;
+use corrosion_host_agent::docker_compose::{DockerComposeConfig, DockerComposeSupervisor};
+use corrosion_host_agent::supervisor::{InstanceState, Supervisor};
+
+/// Write a fake `docker` executable that appends its args (space-joined) to
+/// `args_log` and exits with the integer in `exit_file` (0 if absent).
+fn fake_docker(dir: &Path, args_log: &Path, exit_file: &Path) -> PathBuf {
+    let script = dir.join("fakedocker");
+    let body = format!(
+        "#!/bin/sh\nprintf '%s\\n' \"$*\" >> '{}'\nexit \"$(cat '{}' 2>/dev/null || echo 0)\"\n",
+        args_log.display(),
+        exit_file.display(),
+    );
+    std::fs::write(&script, body).unwrap();
+    let mut perms = std::fs::metadata(&script).unwrap().permissions();
+    perms.set_mode(0o755);
+    std::fs::set_permissions(&script, perms).unwrap();
+    script
+}
+
+fn dune_instance(command: Vec<String>, service: Option<String>) -> InstanceConfig {
+    InstanceConfig {
+        id: "dune-main".to_string(),
+        game: "dune".to_string(),
+        root: PathBuf::from("/tmp"),
+        label: None,
+        executable: None,
+        args: vec![],
+        working_dir: None,
+        rcon: None,
+        steamcmd: None,
+        docker_compose: Some(DockerComposeConfig {
+            file: Some(PathBuf::from("docker-compose.yml")),
+            project: Some("duneproj".to_string()),
+            service,
+            command: Some(command),
+        }),
+    }
+}
+
+#[tokio::test]
+async fn start_runs_compose_up_detached_and_sets_running() {
+    let dir = tempfile::tempdir().unwrap();
+    let args_log = dir.path().join("args.log");
+    let exit_file = dir.path().join("exit");
+    let docker = fake_docker(dir.path(), &args_log, &exit_file);
+
+    let sup = DockerComposeSupervisor::new(&dune_instance(
+        vec![docker.to_string_lossy().into_owned()],
+        None,
+    ));
+    assert_eq!(sup.state(), InstanceState::Stopped);
+
+    sup.clone().start().await.expect("compose up should succeed");
+    assert_eq!(sup.state(), InstanceState::Running);
+
+    let logged = std::fs::read_to_string(&args_log).unwrap();
+    assert!(logged.contains("up -d"), "expected `up -d`; got: {logged}");
+    assert!(logged.contains("-p duneproj"), "expected project flag; got: {logged}");
+    assert!(logged.contains("-f docker-compose.yml"), "expected file flag; got: {logged}");
+}
+
+#[tokio::test]
+async fn stop_runs_compose_stop_and_sets_stopped() {
+    let dir = tempfile::tempdir().unwrap();
+    let args_log = dir.path().join("args.log");
+    let exit_file = dir.path().join("exit");
+    let docker = fake_docker(dir.path(), &args_log, &exit_file);
+
+    let sup = DockerComposeSupervisor::new(&dune_instance(
+        vec![docker.to_string_lossy().into_owned()],
+        None,
+    ));
+    sup.clone().start().await.expect("up");
+    sup.clone().stop().await.expect("compose stop should succeed");
+    assert_eq!(sup.state(), InstanceState::Stopped);
+    assert_eq!(sup.uptime_seconds().await, 0);
+
+    let logged = std::fs::read_to_string(&args_log).unwrap();
+    assert!(logged.lines().any(|l| l.contains("stop")), "expected a `stop` call; got: {logged}");
+}
+
+#[tokio::test]
+async fn restart_runs_compose_restart() {
+    let dir = tempfile::tempdir().unwrap();
+    let args_log = dir.path().join("args.log");
+    let exit_file = dir.path().join("exit");
+    let docker = fake_docker(dir.path(), &args_log, &exit_file);
+
+    let sup = DockerComposeSupervisor::new(&dune_instance(
+        vec![docker.to_string_lossy().into_owned()],
+        None,
+    ));
+    sup.clone().restart().await.expect("compose restart should succeed");
+    assert_eq!(sup.state(), InstanceState::Running);
+
+    let logged = std::fs::read_to_string(&args_log).unwrap();
+    assert!(logged.contains("restart"), "expected `restart`; got: {logged}");
+}
+
+#[tokio::test]
+async fn single_service_is_targeted() {
+    let dir = tempfile::tempdir().unwrap();
+    let args_log = dir.path().join("args.log");
+    let exit_file = dir.path().join("exit");
+    let docker = fake_docker(dir.path(), &args_log, &exit_file);
+
+    let sup = DockerComposeSupervisor::new(&dune_instance(
+        vec![docker.to_string_lossy().into_owned()],
+        Some("gameserver".to_string()),
+    ));
+    sup.clone().start().await.expect("up");
+
+    let logged = std::fs::read_to_string(&args_log).unwrap();
+    assert!(
+        logged.contains("up -d gameserver"),
+        "service must be appended after `up -d`; got: {logged}"
+    );
+}
+
+#[tokio::test]
+async fn compose_failure_errors_and_reverts_state() {
+    let dir = tempfile::tempdir().unwrap();
+    let args_log = dir.path().join("args.log");
+    let exit_file = dir.path().join("exit");
+    std::fs::write(&exit_file, "1").unwrap(); // make the fake docker fail
+    let docker = fake_docker(dir.path(), &args_log, &exit_file);
+
+    let sup = DockerComposeSupervisor::new(&dune_instance(
+        vec![docker.to_string_lossy().into_owned()],
+        None,
+    ));
+    let err = sup.clone().start().await.expect_err("nonzero compose exit must fail");
+    assert!(err.to_string().contains("compose up failed"), "got: {err}");
+    assert_eq!(sup.state(), InstanceState::Stopped, "failed start must revert to Stopped");
+}
+
+#[tokio::test]
+async fn missing_docker_binary_errors_cleanly() {
+    let sup = DockerComposeSupervisor::new(&dune_instance(
+        vec!["/nonexistent/docker-xyz".to_string()],
+        None,
+    ));
+    let err = sup.clone().start().await.expect_err("missing docker must fail");
+    assert!(err.to_string().contains("docker"), "error should mention docker: {err}");
+    assert_eq!(sup.state(), InstanceState::Stopped);
+}