test(nextjs): Add bun e2e test app

[chargome]

• Adds a new E2E test application (nextjs-16-bun) that runs Next.js 16 on Bun's runtime via bun --bun next build/start
• Update CI to pick up this test for the bun runtime

Some limitations we ran into:

1. Outgoing fetch trace propagation is broken

sentry-trace and baggage headers are not attached to outgoing fetch() requests. The OTel nativeNodeFetchIntegration does not intercept Bun's native fetch implementation, so distributed tracing across services does not work. The inbound request starts a new trace instead of continuing the caller's trace.

2. HTTP request headers not extracted as span attributes

Inbound HTTP request headers (e.g. User-Agent, custom headers) are not populated as http.request.header.* attributes on server spans. The OTel HTTP instrumentation doesn't extract these when running on Bun.

Will create tickets for the findings.

ref https://linear.app/getsentry/issue/FE-713/investigate-nextjsbun-setup

[linear]

FE-713 Investigate Next.js+Bun setup

[github-actions]

Codecov Results 📊

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Generated by Codecov Action

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	9,101	-	9,125	-0%
GET With Sentry	1,684	19%	1,602	+5%
GET With Sentry (error only)	6,171	68%	5,883	+5%
POST Baseline	1,179	-	1,176	+0%
POST With Sentry	591	50%	561	+5%
POST With Sentry (error only)	1,015	86%	1,019	-0%
MYSQL Baseline	3,278	-	3,170	+3%
MYSQL With Sentry	469	14%	434	+8%
MYSQL With Sentry (error only)	2,677	82%	2,594	+3%

View base workflow run

[s1gr1d]

Q: is this still nodejs?

[chargome]

Still node yes