Document RUM user context integration for client SDKs

[leoromanovsky]

Motivation

Client Feature Flags SDKs that integrate with RUM can reuse the RUM user as default evaluation context. The shared client documentation needs to explain attribute mapping, precedence, initialization order, and user lifecycle updates without duplicating the behavior across individual SDK guides.

Changes

• Add a concise Use RUM user context for evaluation section to the client Feature Flags landing page.
• Document targeting-key mapping, primitive attribute filtering, application-context precedence, and nested-value exclusion.
• Explain initialization and context reconciliation after login, logout, or account changes.
• Cover the shared behavior across Web, Android, Dart/Flutter, iOS, React Native, and Unity.

Decisions

• Keep the cross-client contract on the existing client landing page instead of introducing a separate page or navigation item.
• Describe user updates through each platform's RUM API and context reconciliation through its Feature Flags API.
• Avoid platform-specific method names so additional client SDKs fit the same contract.

Verification

• Vale 3.9.1 reports no new findings on the changed section.
• git diff --check passed.
• Repository alias, generated-content tracking, and section-index checks passed.

Merge readiness

• Ready for merge

AI assistance

Used Codex to inspect the client implementation behavior, draft the shared contract, and run documentation validation. The content was reviewed against the implementation behavior before publication.

Additional notes

Related implementations:

• feat(browser): include RUM user in evaluation context openfeature-js-client#354
• feat(openfeature): include RUM user in evaluation context dd-sdk-reactnative#1363

[leoromanovsky]

/review

[github-actions]

🤖 Automated review by Claude. AI-generated; verify before acting.

One minor consistency nit on platform naming. Otherwise the new section reads clearly.

_{Reviewed f3ebb3dc827eb74da0fb52b18a3ca90d2dc94bfe — workflow run}

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/leo.romanovsky/rum-user-context-docs/feature_flags/client/

[btthomas]

Can we add the following line somewhere:

A field with an undefined value passed to OpenFeature context suppresses the corresponding RUM attribute and is therefor omitted from the effective context used by the flagging evaluator and downstream telemetry.