Add reproduction for sentry-javascript#18962

[nicohrubec]

Summary

• Reproduction for Sentry breaking OpenAI STREAMING sentry-javascript#18962
• Uses langchain v1 createAgent with agent.stream() and streamMode: ["messages"] in a NestJS app with @sentry/nestjs

Test Results

On latest versions, the bug does not reproduce:

Endpoint	Sentry	Content Chunks	First Byte	Total
/stream-agent	OFF	~40	~0.7s	~1.2s
/stream-agent	ON	~46	~0.5s	~1.0s
/stream-model	ON	~41	~0.7s	~1.1s

Both agent and model streaming work correctly with @sentry/nestjs@10.42.0.

How to test

cd sentry-javascript/18962
npm install
# Add OPENAI_API_KEY to .env file
npm run start:without-sentry   # baseline
npm run start:with-sentry      # compare
curl http://localhost:3000/stream-agent

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Caret version range prevents bug reproduction

Medium Severity

The @sentry/nestjs dependency uses ^10.41.0 (caret range), which resolves to the latest 10.x on npm install. The README explicitly states the bug does not reproduce on @sentry/nestjs@10.42.0 (the version a fresh install gets). This means anyone cloning and running this reproduction will not observe the reported bug. For the reproduction to be useful, the version needs to be pinned to an exact version where the bug manifests. Additionally, the README suggests "pinning to 10.41.0 may reproduce it," but notes the fix was in 10.39.0 — so 10.41.0 already includes the fix, making that guidance contradictory.

Additional Locations (1)

• sentry-javascript/18962/README.md#L10-L21