test(e2e): assert the multi-bundle problem union in the browser

Breaking both bundles shows the union of their problems in the shared
overlay — paginated one per page, in whichever order the compilers
finished. The two jsdom equivalents are removed: the union test, and
no-apply-on-errored-builds, which the multi-compiler console snapshot
already documents (no "Checking for updates" follows a bundle's error
report).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: bjohansebas

test/client.test.js

@@ -114,20 +114,6 @@ describe("client", () => {
       jest.restoreAllMocks();
     });
 
-    it("does not trigger webpack on errored builds", () => {
-      EventSourceStub.lastInstance().onmessage(
-        makeMessage({
-          action: "built",
-          time: 100,
-          hash: "1234567890abcdef",
-          errors: ["Something broke"],
-          warnings: [],
-          modules: [],
-        }),
-      );
-      expect(processUpdate).not.toHaveBeenCalled();
-    });
-
     it("updates overlay when an errored build becomes a warning", () => {
       const es = EventSourceStub.lastInstance();
       es.onmessage(
@@ -202,52 +188,6 @@ describe("client", () => {
     });
   });
 
-  describe("with multi-compiler payloads", () => {
-    let EventSourceStub;
-
-    beforeEach(() => {
-      EventSourceStub = makeEventSourceStub();
-      globalThis.EventSource = EventSourceStub;
-      jest.spyOn(console, "info").mockImplementation(() => {});
-      jest.spyOn(console, "log").mockImplementation(() => {});
-      jest.spyOn(console, "warn").mockImplementation(() => {});
-      jest.spyOn(console, "error").mockImplementation(() => {});
-      loadClient();
-    });
-
-    afterEach(() => {
-      jest.restoreAllMocks();
-    });
-
-    it("shows the union of problems from every broken bundle", () => {
-      const es = EventSourceStub.lastInstance();
-      es.onmessage(
-        makeMessage({
-          action: "built",
-          name: "app",
-          time: 100,
-          hash: "app-hash",
-          errors: ["app broke"],
-          warnings: [],
-        }),
-      );
-      es.onmessage(
-        makeMessage({
-          action: "built",
-          name: "admin",
-          time: 100,
-          hash: "admin-hash",
-          errors: ["admin broke too"],
-          warnings: [],
-        }),
-      );
-      expect(clientOverlay.showProblems).toHaveBeenLastCalledWith("errors", [
-        "app broke",
-        "admin broke too",
-      ]);
-    });
-  });
-
   describe("with overlay warnings enabled via the dev-server-shaped option", () => {
     let EventSourceStub;
 

test/e2e/multi-compiler.test.js

@@ -151,6 +151,49 @@ describe("multi-compiler (browser)", () => {
     expect(normalizeConsole(console_.messages)).toMatchSnapshot();
   });
 
+  it("shows the union of problems from every broken bundle", async () => {
+    app = await createHotApp({
+      apps: [
+        { name: "app", code: bundleApp("app", "app-v1") },
+        { name: "widget", code: bundleApp("widget", "widget-v1") },
+      ],
+    });
+    ({ page, browser } = await runBrowser());
+
+    await page.goto(app.url);
+    await waitForText(page, "out-app", "app-v1");
+    await waitForText(page, "out-widget", "widget-v1");
+
+    app.edit("app", "broken app {{{");
+    app.edit("widget", "broken widget {{{");
+
+    const handle = await page.waitForSelector(`#${OVERLAY_ID}`, {
+      timeout: 30000,
+    });
+    const frame = await handle.contentFrame();
+
+    // Both bundles' problems share the overlay: the pager counts the union
+    // (one problem per page; which bundle finishes breaking first varies).
+    await frame.waitForFunction(
+      () => document.body.textContent.includes("1 / 2"),
+      { timeout: 30000 },
+    );
+
+    const firstPage = await frame.evaluate(() => document.body.textContent);
+
+    await frame.click('[aria-label="Next problem"]');
+    await frame.waitForFunction(
+      () => document.body.textContent.includes("2 / 2"),
+      { timeout: 30000 },
+    );
+
+    const secondPage = await frame.evaluate(() => document.body.textContent);
+    const union = firstPage + secondPage;
+
+    expect(union).toContain("> broken app");
+    expect(union).toContain("> broken widget");
+  });
+
   it("keeps one bundle's overlay errors while a sibling rebuilds successfully", async () => {
     app = await createHotApp({
       apps: [