feat: restore/persist app state in server runtime with queued writes

test/server.test.js

@@ -2,7 +2,7 @@
 
 const test = require("node:test");
 const assert = require("node:assert/strict");
-const { mapToAppRequest, normalizeHeaders } = require("../src/server");
+const { mapToAppRequest, normalizeHeaders, createMutationPersister } = require("../src/server");
 
 test("normalizeHeaders lowercases and joins array values", () => {
   const headers = normalizeHeaders({
@@ -31,3 +31,21 @@ test("mapToAppRequest extracts method/path/headers/body correctly", () => {
   assert.equal(request.headers["x-signature"], "sha256=abc");
   assert.equal(request.rawBody, "{\"ok\":true}");
 });
+
+test("createMutationPersister writes sequentially and flush waits", async () => {
+  const saved = [];
+  const stateStore = {
+    async save(state) {
+      await new Promise((resolve) => setTimeout(resolve, 5));
+      saved.push(state.id);
+    },
+  };
+
+  const persister = createMutationPersister({ stateStore, logger: { error() {} } });
+
+  persister.enqueue({ id: "s1" });
+  persister.enqueue({ id: "s2" });
+  await persister.flush();
+
+  assert.deepEqual(saved, ["s1", "s2"]);
+});