triggerdotdev · ericallam · May 10, 2026
diff --git a/packages/trigger-sdk/src/v3/chat-tab-coordinator.test.ts b/packages/trigger-sdk/src/v3/chat-tab-coordinator.test.ts
@@ -0,0 +1,176 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { ChatTabCoordinator } from "./chat-tab-coordinator.js";
+
+// Mock BroadcastChannel for testing
+class MockBroadcastChannel {
+  static instances: MockBroadcastChannel[] = [];
+  onmessage: ((event: MessageEvent) => void) | null = null;
+  closed = false;
+
+  constructor(public name: string) {
+    MockBroadcastChannel.instances.push(this);
+  }
+
+  postMessage(data: unknown): void {
+    if (this.closed) return;
+    // Deliver to all OTHER instances on the same channel
+    for (const instance of MockBroadcastChannel.instances) {
+      if (instance !== this && instance.name === this.name && !instance.closed) {
+        instance.onmessage?.({ data } as MessageEvent);
+      }
+    }
+  }
+
+  close(): void {
+    this.closed = true;
+    MockBroadcastChannel.instances = MockBroadcastChannel.instances.filter((i) => i !== this);
+  }
+}
+
+describe("ChatTabCoordinator", () => {
+  beforeEach(() => {
+    MockBroadcastChannel.instances = [];
+    vi.stubGlobal("BroadcastChannel", MockBroadcastChannel);
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.useRealTimers();
+  });
+
+  it("tab A claims, tab B sees isReadOnly", () => {
+    const a = new ChatTabCoordinator();
+    const b = new ChatTabCoordinator();
+
+    expect(b.isReadOnly("chat-1")).toBe(false);
+
+    a.claim("chat-1");
+
+    expect(b.isReadOnly("chat-1")).toBe(true);
+    expect(a.isReadOnly("chat-1")).toBe(false); // Owner is not read-only
+
+    a.dispose();
+    b.dispose();
+  });
+
+  it("tab A releases, tab B sees isReadOnly = false", () => {
+    const a = new ChatTabCoordinator();
+    const b = new ChatTabCoordinator();
+
+    a.claim("chat-1");
+    expect(b.isReadOnly("chat-1")).toBe(true);
+
+    a.release("chat-1");
+    expect(b.isReadOnly("chat-1")).toBe(false);
+
+    a.dispose();
+    b.dispose();
+  });
+
+  it("fires listener on claim and release", () => {
+    const a = new ChatTabCoordinator();
+    const b = new ChatTabCoordinator();
+    const listener = vi.fn();
+    b.addListener(listener);
+
+    a.claim("chat-1");
+    expect(listener).toHaveBeenCalledWith("chat-1", true);
+
+    a.release("chat-1");
+    expect(listener).toHaveBeenCalledWith("chat-1", false);
+
+    a.dispose();
+    b.dispose();
+  });
+
+  it("removeListener stops notifications", () => {
+    const a = new ChatTabCoordinator();
+    const b = new ChatTabCoordinator();
+    const listener = vi.fn();
+    b.addListener(listener);
+    b.removeListener(listener);
+
+    a.claim("chat-1");
+    expect(listener).not.toHaveBeenCalled();
+
+    a.dispose();
+    b.dispose();
+  });
+
+  it("claim returns false when another tab holds the chatId", () => {
+    const a = new ChatTabCoordinator();
+    const b = new ChatTabCoordinator();
+
+    expect(a.claim("chat-1")).toBe(true);
+    expect(b.claim("chat-1")).toBe(false);
+
+    a.dispose();
+    b.dispose();
+  });
+
+  it("supports multiple independent chatIds", () => {
+    const a = new ChatTabCoordinator();
+    const b = new ChatTabCoordinator();
+
+    a.claim("chat-1");
+    b.claim("chat-2");
+
+    expect(a.isReadOnly("chat-1")).toBe(false);
+    expect(a.isReadOnly("chat-2")).toBe(true);
+    expect(b.isReadOnly("chat-1")).toBe(true);
+    expect(b.isReadOnly("chat-2")).toBe(false);
+
+    a.dispose();
+    b.dispose();
+  });
+
+  it("heartbeat timeout clears stale claim from crashed tab", () => {
+    const a = new ChatTabCoordinator();
+    const b = new ChatTabCoordinator();
+    const listener = vi.fn();
+    b.addListener(listener);
+
+    a.claim("chat-1");
+    expect(b.isReadOnly("chat-1")).toBe(true);
+
+    // Simulate tab A crashing (close its channel, stop heartbeats)
+    a.dispose();
+
+    // Advance past heartbeat timeout (10s)
+    vi.advanceTimersByTime(11_000);
+
+    expect(b.isReadOnly("chat-1")).toBe(false);
+    expect(listener).toHaveBeenCalledWith("chat-1", false);
+
+    b.dispose();
+  });
+
+  it("dispose releases all claims", () => {
+    const a = new ChatTabCoordinator();
+    const b = new ChatTabCoordinator();
+
+    a.claim("chat-1");
+    a.claim("chat-2");
+    expect(b.isReadOnly("chat-1")).toBe(true);
+    expect(b.isReadOnly("chat-2")).toBe(true);
+
+    a.dispose();
+    expect(b.isReadOnly("chat-1")).toBe(false);
+    expect(b.isReadOnly("chat-2")).toBe(false);
+
+    b.dispose();
+  });
+
+  it("gracefully degrades when BroadcastChannel is unavailable", () => {
+    vi.stubGlobal("BroadcastChannel", undefined);
+
+    const coord = new ChatTabCoordinator();
+
+    // All operations are no-ops
+    expect(coord.claim("chat-1")).toBe(true);
+    expect(coord.isReadOnly("chat-1")).toBe(false);
+    coord.release("chat-1"); // No error
+    coord.dispose(); // No error
+  });
+});