✨ Add @datadog/browser-native isolation layer for browser APIs

[mormubis]

Motivation

Create a clean isolation layer between SDK code and native browser APIs. The long-term goal is to scope BrowserStack unit tests exclusively to this package — all other packages can then run without real-browser testing since their browser API access goes through testable wrappers.

Changes

New package: @datadog/browser-native

Zero-dependency package at the base of the dependency graph (below @datadog/browser-core). Exposes native browser API callsites as standalone named functions, matching browser API names where applicable and using a getter/setter convention for property accesses.

Exports:

• fetch / sendBeacon — network APIs (with Zone.js bypass for fetch)
• addEventListener / removeEventListener — event APIs (with Zone.js bypass + EventTarget.prototype pattern)
• getCookie / setCookie — document.cookie accessor
• getReadyState — document.readyState
• getVisibilityState — document.visibilityState
• now — performance.now()

Migration: packages/core/src/browser/

Updated all direct native callsites in core/src/browser/ to import from @datadog/browser-native instead:

• fetch.ts → re-exports fetch from @datadog/browser-native
• cookie.ts → uses getCookie / setCookie
• addEventListener.ts → uses addEventListener / removeEventListener (removes manual listenerTarget computation and getZoneJsOriginalValue calls)
• runOnReadyState.ts → uses getReadyState
• pageMayExitObservable.ts → uses getVisibilityState

Note: Planning artifacts (design doc, implementation plan) are in .planning/plans/. This code was largely AI agent generated.

Test instructions

yarn test:unit
yarn typecheck
yarn lint

All unit tests (3226), typecheck, and lint pass.

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

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

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I have read the CLA Document and I hereby sign the CLA

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1 out of 2 committers have signed the CLA.
✅ (mormubis)[https://github.com/mormubis]
❌ @claude
_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	171.96 KiB	172.63 KiB	+686 B	+0.39%	✅
Rum Profiler	4.67 KiB	4.67 KiB	-1 B	-0.02%	✅
Rum Recorder	24.88 KiB	24.88 KiB	-1 B	-0.00%	✅
Logs	56.29 KiB	56.75 KiB	+469 B	+0.81%	✅
Flagging	944 B	944 B	0 B	0.00%	✅
Rum Slim	127.73 KiB	128.20 KiB	+480 B	+0.37%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
addglobalcontext	N/A	0.0042	N/A
addaction	N/A	0.013	N/A
adderror	N/A	0.0127	N/A
addtiming	N/A	0.003	N/A
startview	N/A	0.0137	N/A
startstopsessionreplayrecording	N/A	0.0007	N/A
logmessage	N/A	0.0143	N/A

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
addglobalcontext	N/A	26.42 KiB	N/A
addaction	N/A	115.80 KiB	N/A
addtiming	N/A	26.61 KiB	N/A
adderror	N/A	114.30 KiB	N/A
startstopsessionreplayrecording	N/A	25.61 KiB	N/A
startview	N/A	502.69 KiB	N/A
logmessage	N/A	44.98 KiB	N/A

🔗 RealWorld

[datadog-datadog-prod-us1-2]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 62.79%
• Overall Coverage: 77.08% (-0.08%)

_{This comment will be updated automatically if new data arrives.
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