⚗️ [FFL-3067] Add Feature Flags lifecycle telemetry transport

[btthomas]

Motivation

Add the Browser SDK transport required by FFL-3067 so Feature Flags lifecycle events can reach the dedicated, non-billable flagtelemetry Event Platform track.

Changes

• Send all seven Feature Flags lifecycle event payloads directly to /api/v2/flagtelemetry in every configured Datadog site.
• Reuse Browser SDK batching, retry, page-exit delivery, proxy, and client-token support without requiring the RUM or Logs product SDK to start.
• Keep lifecycle events unsampled, respect tracking consent, and isolate transport failures from the provider.
• Deduplicate lifecycle events once per runtime, errors by fixed error code, and configuration receipt once for each source.
• Keep configuration versions optional so SDKs with a real configuration version can report one.
• Omit invalid JavaScript configuration timestamps before serialization.
• Extend the shared endpoint builder with the flagtelemetry track. The OpenFeature provider explicitly starts this transport when its debugMode is enabled. Implementation was Codex-assisted.

Test instructions

• yarn test:unit --single-run --browsers ChromeHeadless
• yarn typecheck
• yarn api:check
• yarn format
• yarn lint
• yarn build

All 5,136 Browser SDK unit tests pass locally.

Rollout notes

• Validate volume and storage cost before enabling unsampled traffic at scale; this is tracked by FFL-3064.
• This transport uses direct HTTP. WebViews that require the native event bridge and pages whose CSP blocks the intake need a follow-up delivery path.
• Complete a staging end-to-end test across Browser SDK, intake, worker, Event Query, and ffe-service before production rollout.

Related PRs

• OpenFeature provider emission: [FFL-3068] Emit Feature Flags lifecycle telemetry openfeature-js-client#381

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

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Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	182.88 KiB	182.88 KiB	0 B	0.00%	✅
Rum Profiler	8.43 KiB	8.43 KiB	0 B	0.00%	✅
Rum Recorder	28.20 KiB	28.20 KiB	0 B	0.00%	✅
Logs	58.66 KiB	58.66 KiB	0 B	0.00%	✅
Rum Salesforce	N/A	140.92 KiB	N/A	N/A	N/A
Rum Slim	140.91 KiB	140.91 KiB	0 B	0.00%	✅
Worker	22.96 KiB	22.96 KiB	0 B	0.00%	✅
Rum Shopify	N/A	210.57 KiB	N/A	N/A	N/A
Rum-shopify Profiler	N/A	8.43 KiB	N/A	N/A	N/A
Rum-shopify Recorder	N/A	3.74 KiB	N/A	N/A	N/A

[datadog-datadog-prod-us1]

 

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🎯 Code Coverage (details)
• Patch Coverage: 83.33%
• Overall Coverage: 77.07% (+0.03%)

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