e2e: Fix flaky login and redirect tests

Resolve flakiness in E2E tests by using deterministic waiting mechanisms for backend API responses.

- Login Test (`login.spec.ts`):
  - Make the syncing state screenshot test deterministic by intercepting the `/v1/users/me/ping` API request and blocking it using a Promise until both light and dark theme screenshots are captured. This prevents the UI from prematurely transitioning to the idle state, which was causing race conditions and snapshot mismatches (especially in WebKit).

- Redirect Tests (`feature-page.spec.ts`, `utils.ts`):
  - Synchronize E2E tests by waiting for backend API GET responses before asserting redirects, rather than relying on page load events or timing out.
  - In `feature-page.spec.ts`:
    - Update `redirects for a moved feature` test to wait for both the redirect response (`old-feature`) and the redirect target response (`new-feature`), filtering both by `GET` method to avoid matching CORS `OPTIONS` preflights. This ensures the test doesn't assert the URL before the redirect target has finished loading, resolving failures on cold start cache misses.
    - Update `shows gone page for a split feature` to wait for the `before-split-feature` GET response before asserting the 410 URL.
  - In `utils.ts`:
    - Update `goTo404Page` helper to wait for the feature's GET response before asserting the 404 URL.

This shifts network wait times to the safe 30-second default timeout of `waitForResponse`, preventing them from eating into the strict 5-second assertion timeout of `toHaveURL` in resource-constrained CI environments.

Author: jcscottiii

e2e/tests/feature-page.spec.ts

@@ -214,12 +214,19 @@ test('date range changes are preserved in the URL', async ({page}) => {
 
 test('redirects for a moved feature', async ({page, browserName}) => {
   test.skip(browserName === 'webkit', 'Skipping webkit due to flakiness');
-  // Wait for the app to fetch the old feature data which triggers the redirect.
-  const responsePromise = page.waitForResponse(response =>
-    response.url().includes('/v1/features/old-feature'),
+  const oldResponsePromise = page.waitForResponse(
+    response =>
+      response.url().includes('/v1/features/old-feature') &&
+      response.request().method() === 'GET',
+  );
+  const newResponsePromise = page.waitForResponse(
+    response =>
+      response.url().includes('/v1/features/new-feature') &&
+      response.request().method() === 'GET',
   );
   await page.goto('http://localhost:5555/features/old-feature');
-  await responsePromise;
+  await oldResponsePromise;
+  await newResponsePromise;
 
   // Expect the URL to be updated to the new feature's URL.
   await expect(page).toHaveURL(
@@ -248,7 +255,14 @@ test('redirects for a moved feature', async ({page, browserName}) => {
 });
 
 test('shows gone page for a split feature', async ({page}) => {
+  // Wait for the API request to complete before checking for redirect.
+  const responsePromise = page.waitForResponse(
+    response =>
+      response.url().includes('/v1/features/before-split-feature') &&
+      response.request().method() === 'GET',
+  );
   await page.goto('http://localhost:5555/features/before-split-feature');
+  await responsePromise;
 
   // Expect to be redirected to the 'feature-gone-split' page.
   await expect(page).toHaveURL(

e2e/tests/login.spec.ts

@@ -28,9 +28,14 @@ test.describe('Login Component States', () => {
   test('displays spinner and is disabled during profile sync', async ({
     page,
   }) => {
-    // Intercept the pingUser request to introduce a delay.
+    let resolvePing: (() => void) | undefined;
+    const pingPromise = new Promise<void>(resolve => {
+      resolvePing = resolve;
+    });
+
+    // Intercept the pingUser request and hold it.
     await page.route('**/v1/users/me/ping', async route => {
-      await new Promise(resolve => setTimeout(resolve, 1000)); // Delay to ensure 'syncing' state is capturable
+      await pingPromise;
       await route.continue();
     });
 
@@ -58,6 +63,11 @@ test.describe('Login Component States', () => {
       },
     );
 
+    // Resolve the ping to let the sync complete.
+    if (resolvePing) {
+      resolvePing();
+    }
+
     // Now, wait for the sync to complete and verify the final state.
     await expect(loginButton.locator('sl-spinner')).toBeHidden();
     await expect(loginButton).not.toBeDisabled();

e2e/tests/utils.ts

@@ -261,7 +261,14 @@ export async function freezeAnimations(page: Page) {
 }
 
 export async function goTo404Page(page: Page, query: string): Promise<void> {
+  const responsePromise = page.waitForResponse(
+    response =>
+      response.url().includes(`/v1/features/${query}`) &&
+      response.request().method() === 'GET',
+  );
   await page.goto(`${BASE_URL}/features/${query}`);
+  await responsePromise;
+
   await expect(page).toHaveURL(
     `${BASE_URL}/errors-404/feature-not-found?q=${query}`,
   );