feat(FN-4370): complete Step 1 — fix badge null-merge semantics

Fusion-Task-Id: FN-4370
Fusion-Task-Lineage: c18188d5-c478-4233-943f-943b0125b271

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

@@ -31,6 +31,22 @@ vi.mock("../../hooks/useTaskDiffStats", () => ({
   useTaskDiffStats: (...args: any[]) => useTaskDiffStatsMock(...args),
 }));
 
+const badgeUpdatesMock = new Map<string, any>();
+const subscribeToBadgeMock = vi.fn();
+const unsubscribeFromBadgeMock = vi.fn();
+vi.mock("../../hooks/useBadgeWebSocket", () => ({
+  useBadgeWebSocket: () => ({
+    badgeUpdates: badgeUpdatesMock,
+    isConnected: true,
+    subscribeToBadge: subscribeToBadgeMock,
+    unsubscribeFromBadge: unsubscribeFromBadgeMock,
+  }),
+}));
+
+vi.mock("../../hooks/useBatchBadgeFetch", () => ({
+  getFreshBatchData: vi.fn(() => null),
+}));
+
 // Mock the api module
 vi.mock("../../api", () => ({
   fetchTaskDetail: vi.fn(),
@@ -90,6 +106,9 @@ const highFanout = {
 afterEach(() => {
   vi.useRealTimers();
   useTaskDiffStatsMock.mockReturnValue({ stats: null, loading: false });
+  badgeUpdatesMock.clear();
+  subscribeToBadgeMock.mockReset();
+  unsubscribeFromBadgeMock.mockReset();
 });
 
 describe("TaskCard", () => {
@@ -279,6 +298,31 @@ describe("TaskCard", () => {
     expect(onOpenDetail).not.toHaveBeenCalled();
   });
 
+  it("renders GitHub badge from live websocket data even when task payload has no badge fields", () => {
+    badgeUpdatesMock.set("default:FN-001", {
+      prInfo: {
+        url: "https://github.com/owner/repo/pull/77",
+        number: 77,
+        status: "open",
+        title: "Live PR",
+        headBranch: "feature/live",
+        baseBranch: "main",
+        commentCount: 0,
+      },
+      timestamp: "2026-05-13T12:00:00.000Z",
+    });
+
+    render(
+      <TaskCard
+        task={makeTask({ column: "in-review", prInfo: undefined, issueInfo: undefined })}
+        onOpenDetail={noop}
+        addToast={noop}
+      />,
+    );
+
+    expect(screen.getByRole("link", { name: "#77" })).toBeDefined();
+  });
+
   it("clicking issue badge text does not open the task detail modal", () => {
     const onOpenDetail = vi.fn();
     render(

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

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+import { pickPreferredBadge } from "../TaskCardBadge";
+
+describe("pickPreferredBadge", () => {
+  const taskValue = { number: 1, lastCheckedAt: "2026-05-13T10:00:00.000Z" };
+  const liveValue = { number: 2, lastCheckedAt: "2026-05-13T11:00:00.000Z" };
+
+  it("returns undefined when both values are missing", () => {
+    expect(pickPreferredBadge(undefined, undefined, undefined, undefined)).toBeUndefined();
+  });
+
+  it("returns undefined when live is null and task is missing", () => {
+    expect(pickPreferredBadge(null, "2026-05-13T12:00:00.000Z", undefined, undefined)).toBeUndefined();
+  });
+
+  it("keeps task value when live is null", () => {
+    expect(
+      pickPreferredBadge(null, "2026-05-13T12:00:00.000Z", taskValue, "2026-05-13T10:00:00.000Z"),
+    ).toEqual(taskValue);
+  });
+
+  it("prefers live when newer", () => {
+    expect(
+      pickPreferredBadge(liveValue, "2026-05-13T12:00:00.000Z", taskValue, "2026-05-13T10:00:00.000Z"),
+    ).toEqual(liveValue);
+  });
+
+  it("prefers task when newer", () => {
+    expect(
+      pickPreferredBadge(liveValue, "2026-05-13T10:00:00.000Z", taskValue, "2026-05-13T12:00:00.000Z"),
+    ).toEqual(taskValue);
+  });
+});