push updated state to clients over SSE (ISS-129)

lib/sse.test.ts

@@ -0,0 +1,45 @@
+import { describe, expect, it } from 'vitest';
+import { broadcast, subscribe } from './sse';
+
+// ISS-129 (v0.57.0): the fan-out registry behind /api/events — plain Set semantics, so no DB or
+// server needed. Subscribers leak across tests in this file (module-level state), which is fine:
+// each test only asserts on its own arrays.
+
+describe('lib/sse', () => {
+  it('delivers broadcasts to subscribers and stops after unsubscribe', () => {
+    const a: string[] = [];
+    const b: string[] = [];
+    const unsubA = subscribe((t) => a.push(t));
+    const unsubB = subscribe((t) => b.push(t));
+
+    broadcast('x');
+    expect(a).toEqual(['x']);
+    expect(b).toEqual(['x']);
+
+    unsubA();
+    broadcast('y');
+    expect(a).toEqual(['x']); // unsubscribed — no more events
+    expect(b).toEqual(['x', 'y']);
+    unsubB();
+  });
+
+  it('a throwing subscriber does not break the others', () => {
+    const got: string[] = [];
+    subscribe(() => {
+      throw new Error('boom');
+    });
+    const unsub = subscribe((t) => got.push(t));
+    broadcast('z');
+    expect(got).toEqual(['z']);
+    unsub();
+  });
+
+  it('unsubscribe is idempotent', () => {
+    const got: string[] = [];
+    const unsub = subscribe((t) => got.push(t));
+    unsub();
+    unsub(); // second call must not throw
+    broadcast('w');
+    expect(got).toEqual([]);
+  });
+});