Resolve MockQueue.listen() on a pre-aborted signal

MockQueue.listen() only resolved from an "abort" event listener, so a
signal already aborted before the call left the promise pending
forever and could hang queue-listener teardown in tests.  Return a
resolved promise when the signal is already aborted, and register the
listener with { once: true }.

#806 (comment)

Assisted-by: Claude Code:claude-opus-4-8

Author: 2chanhaeng

packages/fedify/src/federation/tasks/tasks.test.ts

@@ -497,6 +497,23 @@ test("startQueue() task worker", async (t) => {
   );
 });
 
+test("MockQueue.listen() resolves on a pre-aborted signal", async () => {
+  const queue = new MockQueue();
+  const controller = new AbortController();
+  controller.abort();
+  let timer: ReturnType<typeof setTimeout> | undefined;
+  const settled = await Promise.race([
+    queue.listen(() => {}, { signal: controller.signal }).then(() =>
+      "resolved"
+    ),
+    new Promise<string>((resolve) => {
+      timer = setTimeout(() => resolve("pending"), 50);
+    }),
+  ]);
+  clearTimeout(timer);
+  strictEqual(settled, "resolved");
+});
+
 test("processQueuedTask() task dispatch", async (t) => {
   await t.step("drops an unknown task with a warning", async () => {
     const queue = new MockQueue();

packages/fedify/src/testing/tasks.ts

@@ -129,8 +129,11 @@ export class MockQueue implements MessageQueue {
     options?: MessageQueueListenOptions,
   ): Promise<void> {
     this.listenCount++;
+    if (options?.signal?.aborted) return Promise.resolve();
     return new Promise((resolve) => {
-      options?.signal?.addEventListener("abort", () => resolve());
+      options?.signal?.addEventListener("abort", () => resolve(), {
+        once: true,
+      });
     });
   }
 }