test(KB-640): add agent button click handler tests

packages/dashboard/app/components/__tests__/Header.test.tsx

@@ -460,5 +460,49 @@ describe("Header", () => {
       fireEvent.change(input, { target: { value: "test" } });
       expect(onSearchChange).toHaveBeenCalledWith("test");
     });
+
+    it("shows agents button in overflow menu on mobile when onOpenAgents provided", () => {
+      render(<Header onOpenSettings={vi.fn()} onOpenAgents={vi.fn()} />);
+      fireEvent.click(screen.getByTitle("More header actions"));
+      expect(screen.getByText("Manage Agents")).toBeDefined();
+    });
+
+    it("agents overflow menu item calls onOpenAgents when clicked", () => {
+      const onOpenAgents = vi.fn();
+      render(<Header onOpenSettings={vi.fn()} onOpenAgents={onOpenAgents} />);
+      fireEvent.click(screen.getByTitle("More header actions"));
+      fireEvent.click(screen.getByText("Manage Agents"));
+      expect(onOpenAgents).toHaveBeenCalledOnce();
+    });
+  });
+
+  // ── Agents Button ────────────────────────────────────────────────
+
+  it("renders agents button with correct title on desktop", () => {
+    const onOpenAgents = vi.fn();
+    render(<Header onOpenAgents={onOpenAgents} />);
+    const btn = screen.getByTitle("Manage Agents");
+    expect(btn).toBeDefined();
+  });
+
+  it("calls onOpenAgents when agents button is clicked", () => {
+    const onOpenAgents = vi.fn();
+    render(<Header onOpenAgents={onOpenAgents} />);
+    const btn = screen.getByTitle("Manage Agents");
+    fireEvent.click(btn);
+    expect(onOpenAgents).toHaveBeenCalledOnce();
+  });
+
+  it("does not render agents button when onOpenAgents is not provided", () => {
+    render(<Header />);
+    const btn = screen.queryByTitle("Manage Agents");
+    expect(btn).toBeNull();
+  });
+
+  it("agents button has correct data-testid", () => {
+    const onOpenAgents = vi.fn();
+    render(<Header onOpenAgents={onOpenAgents} />);
+    const btn = screen.getByTestId("agents-btn");
+    expect(btn).toBeDefined();
   });
 });