fix(integration): serialize browser add inputs

- serialize extension and deep-link Add-window events
- acknowledge successful extension handling at the frontend boundary
- add regression coverage for ordered input processing

src/utils/serialTaskQueue.test.ts

@@ -0,0 +1,45 @@
+import { describe, expect, it } from 'vitest';
+import { createSerialTaskQueue } from './serialTaskQueue';
+
+describe('createSerialTaskQueue', () => {
+  it('runs tasks in enqueue order and waits for each previous task', async () => {
+    const queue = createSerialTaskQueue();
+    const events: string[] = [];
+    let releaseFirst!: () => void;
+    const firstReleased = new Promise<void>(resolve => {
+      releaseFirst = resolve;
+    });
+
+    const first = queue(async () => {
+      events.push('first-start');
+      await firstReleased;
+      events.push('first-end');
+    });
+    const second = queue(async () => {
+      events.push('second');
+    });
+
+    await new Promise<void>(resolve => setTimeout(resolve, 0));
+    expect(events).toEqual(['first-start']);
+    releaseFirst();
+    await Promise.all([first, second]);
+    expect(events).toEqual(['first-start', 'first-end', 'second']);
+  });
+
+  it('continues with later tasks after a failed task', async () => {
+    const queue = createSerialTaskQueue();
+    const events: string[] = [];
+
+    const failed = queue(async () => {
+      events.push('failed');
+      throw new Error('expected failure');
+    });
+    const continued = queue(async () => {
+      events.push('continued');
+    });
+
+    await expect(failed).rejects.toThrow('expected failure');
+    await expect(continued).resolves.toBeUndefined();
+    expect(events).toEqual(['failed', 'continued']);
+  });
+});

src/utils/serialTaskQueue.ts

@@ -0,0 +1,13 @@
+export type SerialTask = () => void | Promise<void>;
+
+export type SerialTaskQueue = (task: SerialTask) => Promise<void>;
+
+export const createSerialTaskQueue = (): SerialTaskQueue => {
+  let tail: Promise<void> = Promise.resolve();
+
+  return task => {
+    const next = tail.catch(() => undefined).then(task);
+    tail = next.catch(() => undefined);
+    return next;
+  };
+};