feat(core-events): PayloadJobsEventBus (fan-out via IJobQueue)

TDD: red (test-only), then green. PayloadJobsEventBus validates before
enqueueing, names tasks __events.<event>.<consumer> deterministically, and
enqueues one task per subscriber via Promise.all. 3 new tests (11 total).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-events/src/payload-jobs-event-bus.test.ts

@@ -0,0 +1,51 @@
+import { describe, it, expect, vi } from "vitest";
+import { z } from "zod";
+import { defineEvent } from "@/event-descriptor";
+import { PayloadJobsEventBus } from "@/payload-jobs-event-bus";
+import type { IJobQueue } from "@repo/core-shared/jobs";
+
+const evt = defineEvent("auth.user.signed-up", z.object({ userId: z.string() }).strict());
+
+function recordingQueue(): IJobQueue & { enqueued: { taskSlug: string; input: unknown }[] } {
+  const enqueued: { taskSlug: string; input: unknown }[] = [];
+  const q: IJobQueue = {
+    async enqueue(taskSlug, input) {
+      enqueued.push({ taskSlug, input });
+      return { jobId: `recording-${enqueued.length}` };
+    },
+  };
+  return Object.assign(q, { enqueued });
+}
+
+describe("PayloadJobsEventBus", () => {
+  it("validates the payload before enqueueing", async () => {
+    const queue = recordingQueue();
+    const bus = new PayloadJobsEventBus(queue);
+    bus.subscribe(evt, "marketing-pages", vi.fn());
+    await expect(
+      bus.publish(evt, { userId: 42 } as unknown as { userId: string }),
+    ).rejects.toThrow();
+    expect(queue.enqueued).toHaveLength(0);
+  });
+
+  it("enqueues one task per subscriber, naming `__events.<event>.<consumer>`", async () => {
+    const queue = recordingQueue();
+    const bus = new PayloadJobsEventBus(queue);
+    bus.subscribe(evt, "marketing-pages", vi.fn());
+    bus.subscribe(evt, "blog", vi.fn());
+    await bus.publish(evt, { userId: "u1" });
+    expect(queue.enqueued).toHaveLength(2);
+    expect(queue.enqueued.map((e) => e.taskSlug).sort()).toEqual([
+      "__events.auth.user.signed-up.blog",
+      "__events.auth.user.signed-up.marketing-pages",
+    ]);
+    expect(queue.enqueued[0]!.input).toEqual({ userId: "u1" });
+  });
+
+  it("enqueues nothing when no subscribers are registered", async () => {
+    const queue = recordingQueue();
+    const bus = new PayloadJobsEventBus(queue);
+    await bus.publish(evt, { userId: "u1" });
+    expect(queue.enqueued).toHaveLength(0);
+  });
+});