[Flaky CI]: E2E nextjs-16 Test - [chromium] › tests/metrics.test.ts:4:5 › Should emit metrics from server and client

[github-actions]

Flakiness Type

Other / Unknown

Name of Job

E2E nextjs-16 Test

Name of Test

[chromium] › tests/metrics.test.ts:4:5 › Should emit metrics from server and client

Link to Test Run

https://github.com/getsentry/sentry-javascript/actions/runs/26218477452/job/77148343557

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This issue was automatically created.

[linear-code]

JS-2579

[github-actions]

An automated triage pass looked at this but did not produce a fix. Notes for whoever picks this up next:

What I could verify statically (no CI log access in this run):

• Test: dev-packages/e2e-tests/test-applications/nextjs-16/tests/metrics.test.ts — sets up six waitForMetric promises, navigates to /metrics, clicks the Emit button, then awaits all six.
• Page handler: app/metrics/page.tsx — emits three client metrics then await fetch('/metrics/route-handler') (which emits three server metrics).
• Defaults that bound the test: Playwright test timeout = 30s (playwright-config.ts:25); SDK metric flush interval = 5s (DEFAULT_FLUSH_INTERVAL in packages/core/src/client.ts:67).
• With a 5s flush interval and a single click, all six metrics should land well inside the 30s budget, so timing alone shouldn't explain the flake.

Plausible root causes worth checking against the actual log:

1. Hydration race on the Emit button. page.getByText('Emit').click() will dispatch a DOM click as soon as the element is visible, but the React onClick handler isn't wired up until hydration completes. If hydration is slow on CI, the click can be a no-op and no client metrics are emitted. If the log shows the test timing out waiting for test.page.count while server metrics are absent too (because the fetch inside the click handler never fires), this is the most likely cause.
2. Server metric never fired. If the log shows client metrics arrived but server metrics didn't, look at the route handler / proxy connection rather than the page.
3. Just a one-off CI hiccup (event-proxy server slow to come up, network blip, etc.) — the auto-created issues fire on a single failure, so a single occurrence isn't necessarily a real bug.

Suggested next step if (1) is the cause: gate the click on hydration, e.g. await page.waitForLoadState('networkidle') after page.goto, or replace the bare click with a Playwright assertion that the button is actually wired before clicking.

I am not making code changes here because I cannot confirm the failure mode without the job log, and the test infrastructure looks correct on paper.