fix(actor-system): release spawn gate before start

.changeset/release-nested-spawn-gate.md

@@ -0,0 +1,5 @@
+---
+"effect-machine": patch
+---
+
+Allow nested actors to start before their parent spawn returns.

src/actor.ts

@@ -1262,10 +1262,6 @@ const make = Effect.fn("effect-machine.actorSystem.make")(function* () {
     actorRef = actor as unknown as ActorRef<AnyState, unknown>;
     // Register before start — actor is in the map before lifecycle hooks fire
     yield* registerActor(id, actor);
-    // Auto-start: system.spawn returns a running actor
-    yield* actor.start.pipe(
-      Effect.catchCause((cause) => actor.stop.pipe(Effect.andThen(Effect.failCause(cause)))),
-    );
     return actor;
   });
 
@@ -1282,11 +1278,14 @@ const make = Effect.fn("effect-machine.actorSystem.make")(function* () {
     options?: SystemSpawnOptions<S, E, Input>,
   ): Effect.Effect<ActorRef<S, E, Output>, DuplicateActorError, R> => {
     const id = actorSystemId(idOrKey);
-    return withSpawnGate(spawnRegular(id, machine, options)) as Effect.Effect<
-      ActorRef<S, E, Output>,
-      DuplicateActorError,
-      R
-    >;
+    return withSpawnGate(spawnRegular(id, machine, options)).pipe(
+      Effect.flatMap((actor) =>
+        actor.start.pipe(
+          Effect.catchCause((cause) => actor.stop.pipe(Effect.andThen(Effect.failCause(cause)))),
+          Effect.as(actor),
+        ),
+      ),
+    ) as Effect.Effect<ActorRef<S, E, Output>, DuplicateActorError, R>;
   };
 
   function get<S extends AnyState, E, Output>(

test/actor.test.ts

@@ -97,6 +97,30 @@ describe("ActorSystem", () => {
     }).pipe(Effect.provide(ActorSystemDefault)),
   );
 
+  it.scopedLive("registers a nested child before parent spawn returns", () =>
+    Effect.gen(function* () {
+      const ChildState = State({ Active: {} });
+      const ChildEvent = Event({ Stop: {} });
+      const childMachine = Machine.make({
+        state: ChildState,
+        event: ChildEvent,
+        initial: ChildState.Active,
+      });
+      const parentMachine = Machine.make({
+        state: TestState,
+        event: TestEvent,
+        initial: TestState.Idle,
+      }).spawn(TestState.Idle, ({ self }) =>
+        self.spawn("nested-child", childMachine).pipe(Effect.asVoid, Effect.orDie),
+      );
+      const system = yield* ActorSystemService;
+
+      yield* system.spawn("nested-parent", parentMachine);
+
+      expect((yield* system.get("nested-child"))._tag).toBe("Some");
+    }).pipe(Effect.provide(ActorSystemDefault)),
+  );
+
   it.scopedLive("stops actors properly", () =>
     Effect.gen(function* () {
       const machine = Machine.make({