💥 enable propagateTraceBaggage by default

[BenoitZugmeyer]

Motivation

The baggage header propagates RUM session context (session ID, user ID, account ID) to backend services for distributed tracing correlation. Requiring customers to explicitly opt in creates unnecessary friction — it should be on by default, with an explicit opt-out for those who don't want it.

Changes

• configuration.ts: change default from false to true by using !== false instead of !!
• tracer.spec.ts: update expected headers to include baggage by default; use toPlainObject() for the Request case to avoid alphabetical ordering sensitivity
• tracing.scenario.ts: update e2e scenarios — baggage is now expected in checkRequestHeaders by default, rename the old "propagate trace baggage" test to cover user/account specifically, add a new test for propagateTraceBaggage: false

Test instructions

1. Open the sandbox (yarn dev, navigate to http://localhost:8080)
2. Add allowedTracingUrls: ['https://httpbin.org'], service: 'sandbox' to DD_RUM.init() in sandbox/index.html
3. Run fetch('https://httpbin.org/headers').then(r => r.json()).then(j => console.log(j.headers)) — verify Baggage: session.id=... is present
4. Add propagateTraceBaggage: false — reload and repeat — verify Baggage is absent

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	170.61 KiB	170.61 KiB	+3 B	+0.00%	✅
Rum Profiler	4.69 KiB	4.69 KiB	0 B	0.00%	✅
Rum Recorder	24.91 KiB	24.91 KiB	0 B	0.00%	✅
Logs	56.38 KiB	56.38 KiB	0 B	0.00%	✅
Flagging	944 B	944 B	0 B	0.00%	✅
Rum Slim	127.89 KiB	127.89 KiB	+3 B	+0.00%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Pending...

🧠 Memory Performance

Pending...

🔗 RealWorld

[datadog-official]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 76.96% (+0.00%)

_{This comment will be updated automatically if new data arrives.
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[thomas-lebeau]

❓ question: ‏what happen when:

• propagateTraceBaggage: true and no user and account context set?
• propagateTraceBaggage: false and user and account context is set

should we also test for these?

[BenoitZugmeyer]

• propagateTraceBaggage: true and no user and account context set?

This is already covered by various test cases, since propagateTraceBaggage: true is the default now. This assertion ensure the baggage header is set with the session id.

• propagateTraceBaggage: false and user and account context is set

I don't think we really need to test for it, since in this case the header should just not be present?