feat: runtime manager

rtmanager/internal/domain/runtime/transitions.go

@@ -0,0 +1,51 @@
+package runtime
+
+// transitionKey stores one `(from, to)` pair in the allowed-transitions
+// table.
+type transitionKey struct {
+	from Status
+	to   Status
+}
+
+// allowedTransitions stores the set of permitted `(from, to)` status
+// pairs. The four pairs mirror the lifecycle flows frozen in
+// `galaxy/rtmanager/README.md §Lifecycles`:
+//
+//   - running → stopped: graceful stop, observed Docker exit, or
+//     reconcile observing an exited container.
+//   - running → removed: reconcile_dispose when Docker no longer reports
+//     the container at all.
+//   - stopped → running: restart and patch inner start steps.
+//   - stopped → removed: cleanup_container, both the periodic TTL worker
+//     and the admin DELETE endpoint.
+var allowedTransitions = map[transitionKey]struct{}{
+	{StatusRunning, StatusStopped}: {},
+	{StatusRunning, StatusRemoved}: {},
+	{StatusStopped, StatusRunning}: {},
+	{StatusStopped, StatusRemoved}: {},
+}
+
+// AllowedTransitions returns a copy of the `(from, to)` allowed
+// transitions table used by Transition. The returned map is safe to
+// mutate; callers should not rely on iteration order.
+func AllowedTransitions() map[Status][]Status {
+	result := make(map[Status][]Status)
+	for key := range allowedTransitions {
+		result[key.from] = append(result[key.from], key.to)
+	}
+	return result
+}
+
+// Transition reports whether from may transition to next. The function
+// returns nil when the pair is permitted, and an *InvalidTransitionError
+// wrapping ErrInvalidTransition otherwise. It does not touch any store
+// and is safe to call from any layer.
+func Transition(from Status, next Status) error {
+	if !from.IsKnown() || !next.IsKnown() {
+		return &InvalidTransitionError{From: from, To: next}
+	}
+	if _, ok := allowedTransitions[transitionKey{from: from, to: next}]; !ok {
+		return &InvalidTransitionError{From: from, To: next}
+	}
+	return nil
+}