reactRouterV6BrowserTracingIntegration perf issues with React 19.2 (development env only)

[billyvg]

Description

We recently upgraded Sentry to React 19.2 and it's been freezing up when developing locally. Production works fine.

See this slack thread for more context, but removing reactRouterV6BrowserTracingIntegration fixes the perf issue.

For now we've disabled the integration in non-production environments.

[linear]

JS-1034

[billyvg]

To repro, in the sentry repo:

• revert this commit: git revert 286062e88765cec92c321e60afc161a97007c1ee
• run pnpm dev-ui'
• Go to the /replays/ page and click around, you'll notice that it's incredibly slow

[Lms24]

After reproducing this, it appears to be caused by the SDK backfilling measure spans from React 19.2 now emitting custom tracks for component rendering time: https://react.dev/blog/2025/10/01/react-19-2#performance-tracks

These are created via performance.measure() calls, which our SDK extracts and creates spans from when ending the idle span. This is pretty apparent when setting debug: true and observing thousands of these logs:

Sentry Logger [log]: [Tracing] Finishing "measure" span "​Link" with ID 943626a659c8694f
debug-logger.js:92 Sentry Logger [log]: [Tracing] Starting sampled span
  op: measure
  name: ​_c
  ID: 9ecdeabe9ead2784
  parent ID: 8601431d961d9cce
  root ID: 8601431d961d9cce
  root op: pageload
  root description: /issues/
debug-logger.js:92 Sentry Logger [log]: [Tracing] Finishing "measure" span "​_c" with ID 9ecdeabe9ead2784
debug-logger.js:92 Sentry Logger [log]: [Tracing] Starting sampled span
  op: measure
  name: ​Wrapper
  ID: bc3930cdd80a40a2
  parent ID: 8601431d961d9cce
  root ID: 8601431d961d9cce
  root op: pageload
  root description: /issues/

...

We'll need to find a way to exclude these measure spans by default. This generates so many spans that the transaction gets dropped by Relay due to it exceeding the 1000 span limit. Gonna try to come up with a fix today.

[github-actions]

A PR closing this issue has just been released 🚀

This issue was referenced by PR #17905, which was included in the 10.20.0 release.