[@xstate/store] "Async" transitions

.changeset/async-step-store.md

@@ -0,0 +1,29 @@
+---
+'@xstate/store': minor
+---
+
+Add async step support to `createStore(...)` with `await enq.step(stepId, exec)`.
+
+```ts
+const store = createStore({
+  context: {
+    result: undefined as number | undefined
+  },
+  on: {
+    load: async (context, event: { id: string }, enq) => {
+      const result = await enq.step('fetchResult', () => fetchResult(event.id));
+
+      return {
+        ...context,
+        result
+      };
+    }
+  }
+});
+```
+
+This keeps `@xstate/store` aligned with its state-machine-like model: pending
+async work is captured in the snapshot, and step completion is handled through
+explicit followup events. That means an in-progress async transition can be
+replayed deterministically from persisted snapshot state instead of depending on
+an opaque promise continuation.

packages/xstate-store/src/fromStore.ts

@@ -83,6 +83,9 @@ export function fromStore<
           typeof initialContext === 'function'
             ? initialContext(input)
             : initialContext,
+        async: {
+          pending: {}
+        },
         output: undefined,
         error: undefined
       } satisfies StoreSnapshot<TContext>;