diff --git a/packages/web/src/hooks/__tests__/useSessionEvents.mux.test.ts b/packages/web/src/hooks/__tests__/useSessionEvents.mux.test.ts
new file mode 100644
index 000000000..4db3e6a8c
--- /dev/null
+++ b/packages/web/src/hooks/__tests__/useSessionEvents.mux.test.ts
@@ -0,0 +1,38 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { renderHook, waitFor } from "@testing-library/react";
+import { useSessionEvents } from "../useSessionEvents";
+import type { DashboardSession } from "@/lib/types";
+
+const now = new Date().toISOString();
+const s1 = { id: "s1", projectId: "proj", lastActivityAt: now } as unknown as DashboardSession;
+
+describe("useSessionEvents - mux", () => {
+  beforeEach(() => {
+    vi.stubGlobal(
+      "fetch",
+      vi.fn().mockResolvedValue({
+        ok: true,
+        json: async () => ({ sessions: [s1] }),
+      } as unknown as Response),
+    );
+  });
+  afterEach(() => {
+    vi.unstubAllGlobals();
+    vi.clearAllTimers();
+  });
+
+  it("triggers refresh when mux patch contains unknown id", async () => {
+    const initialSessions = [s1];
+    const muxSessions = [
+      { id: "s1", status: "working", activity: "active", attentionLevel: "none", lastActivityAt: now },
+      { id: "s2", status: "working", activity: "active", attentionLevel: "none", lastActivityAt: now },
+    ];
+    renderHook(() => useSessionEvents(initialSessions, "proj", muxSessions));
+    await waitFor(() => {
+      expect(fetch).toHaveBeenCalledWith(
+        "/api/sessions?project=proj",
+        expect.objectContaining({ signal: expect.any(AbortSignal) }),
+      );
+    });
+  });
+});