Default debugger version and embed build identity in snapshots

[watson]

Motivation

The Browser Debugger SDK should be able to pick up the browser build version injected by the Live Debugger build plugin so applications do not need to pass the same deployed build identifier into datadogDebugger.init() a second time.

The debugger snapshot payload also needs applicationId and version so downstream browser-build and source-resolution flows can identify the correct browser build when git tags are unavailable.

Changes

Version defaulting from build metadata

• default datadogDebugger.init().version from the build-plugin metadata when callers omit version
• keep an explicit init({ version }) value authoritative and warn if it disagrees with the injected build-plugin version
• document that version is optional, but browser build lookup and source-aware resolution depend on an immutable deployed build identifier when available

Snapshot build identity

• include applicationId and version as a structured build object inside the debugger.snapshot payload (debugger.snapshot.build = { applicationId, version })
• this replaces the earlier approach of putting application_id as a top-level field and duplicating application_id/version into ddtags, which was vulnerable to tag collision from downstream enrichment
• the build object rides on the existing @debugger.snapshot column projection, so the web UI reads it without any query changes

Version documentation

• document that version is optional in the Browser Debugger README and API docs
• clarify that when provided, version should be the immutable deployed browser build identifier
• clarify graceful degradation when version is absent

Test instructions

Run:

yarn test:unit --spec packages/debugger/src/entries/main.spec.ts
yarn test:unit --spec packages/debugger/src/domain/api.spec.ts

Part of larger effort

This PR is one part of the browser Live Debugger source-resolution work across multiple repositories:

• https://github.com/DataDog/dd-source/pull/415107
• https://github.com/DataDog/dd-source/pull/418329
• https://github.com/DataDog/debugger-backend/pull/2053
• https://github.com/DataDog/web-ui/pull/298258
• Validate optional live-debugger version build-plugins#325
• Source build version from shared metadata.version build-plugins#326

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

[watson]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• Default debugger version and embed build identity in snapshots #4511 👈 (View in Graphite)
• Add Live Debugger package #4449 : 5 other dependent PRs (#4480 , #4503 , #4508 and 2 others)
• Fix TanStack Router lint resolution in test app #4513
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	179.42 KiB	179.42 KiB	0 B	0.00%	✅
Rum Profiler	6.16 KiB	6.16 KiB	0 B	0.00%	✅
Rum Recorder	27.03 KiB	27.03 KiB	0 B	0.00%	✅
Logs	56.80 KiB	56.80 KiB	0 B	0.00%	✅
Rum Slim	135.26 KiB	135.26 KiB	0 B	0.00%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.00545	0.0128	+134.86%
RUM - add action	0.0161	0.0194	+20.50%
RUM - add error	0.013999999999999999	0.0228	+62.86%
RUM - add timing	0.00295	0.0041	+38.98%
RUM - start view	0.01405	0.0195	+38.79%
RUM - start/stop session replay recording	0.0009	0.0009	0.00%
Logs - log message	0.016900000000000002	0.02	+18.34%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	31.62 KiB	31.62 KiB	-7 B
RUM - add action	98.83 KiB	116.63 KiB	+17.80 KiB
RUM - add timing	32.04 KiB	31.75 KiB	-292 B
RUM - add error	102.48 KiB	107.66 KiB	+5.18 KiB
RUM - start/stop session replay recording	31.65 KiB	30.91 KiB	-753 B
RUM - start view	492.03 KiB	494.29 KiB	+2.26 KiB
Logs - log message	102.30 KiB	102.44 KiB	+150 B

🔗 RealWorld

[datadog-prod-us1-4]

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 84.62%
• Overall Coverage: 76.76% (+0.06%)

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