…#18887)

## DESCRIBE YOUR PR

#18775 dropped middleware root spans entirely; this restores them at a
blind 1% (~24k/day), blind because Next.js creates the
`Middleware.execute` root in a detached sandbox before any request data
reaches Sentry, so `tracesSampler` can never classify it.
`middleware.ts` tags that span with `middleware.outcome`
(redirect/rewrite/passthrough), `url.path`, `traffic_type`, and
`device_type` — attributes rather than a span name, because the SDK's
`enhanceMiddlewareRootSpan` unconditionally rewrites
`Middleware.execute` names to `middleware {METHOD}` on the send path and
ignores `sentry.source`. `isMiddlewareRootSpan` now matches both
`http.server.middleware` (SDK v10) and `middleware` (v11) so detection
survives the upgrade.

Note that v10 still emits a duplicate nested middleware span, so volume
may be ~2x until getsentry/sentry-javascript#22904 lands — unrelated to
this rate, and a non-zero rate is what makes that fix observable here at
all. To verify after deploy: `spans · span.op:http.server.middleware ·
release:<new sha>` is non-zero at ~1% of request volume with
`middleware.outcome` populated, and `docs.request.classified` grouped by
`traffic_type` is unchanged.

## IS YOUR CHANGE URGENT?

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to go live.
- [ ] Urgent deadline (GA date, etc.): <!-- ENTER DATE HERE -->
- [ ] Other deadline: <!-- ENTER DATE HERE -->
- [x] None: Not urgent, can wait up to 1 week+

## SLA

- Teamwork makes the dream work, so please add a reviewer to your PRs.
- Please give the docs team up to 1 week to review your PR unless you've
added an urgent due date to it.
Thanks in advance for your help!

## PRE-MERGE CHECKLIST

*Make sure you've checked the following before merging your changes:*

- [ ] Checked Vercel preview for correctness, including links
- [ ] PR was reviewed and approved by any necessary SMEs (subject matter
experts)
- [ ] PR was reviewed and approved by a member of the [Sentry docs
team](https://github.com/orgs/getsentry/teams/docs)

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Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>