refactor(sse): narrow canonical audience scopes

packages/api/src/__tests__/event-bus-debounce.test.ts

@@ -265,4 +265,24 @@ describe("event-bus debounce", () => {
     unsubscribeManager();
     unsubscribeResource();
   });
+
+  it("rejects invalid subscription audiences", () => {
+    expect(() =>
+      eventBus.subscribe(
+        () => undefined,
+        {
+          audiences: ["chapter:capex" as never],
+          includeUnscoped: false,
+        },
+      )).toThrowError("Invalid SSE audience: chapter:capex");
+  });
+
+  it("rejects invalid emitted audiences", () => {
+    expect(() =>
+      eventBus.emit(
+        SSE_EVENT_TYPES.NOTIFICATION_CREATED,
+        { notificationId: "n1" },
+        ["user:" as never],
+      )).toThrowError("Invalid SSE audience: user:");
+  });
 });