[Fiona2016]

Motivation

With remote configuration enabled, a session is drawn on the settings stored by an earlier page, and the settings fetched at start-up only apply to the next session. A page with nothing stored — a first visit, a private window, a browser that clears storage — therefore always drew on the values passed to init. For visitors whose storage does not last until their next session that is every session, so the rates delivered from the console never applied to them.

Changes

• Wait for the first settings when nothing is stored. After tracking consent is granted and before RUM starts, a page with no stored settings (and writable localStorage, and no event bridge) waits for the first settings answer, at most REMOTE_CONFIGURATION_WAIT (1 s). Any answer ends the wait, a failed one included; a late answer is still stored for the next draw. Pages with settings stored start exactly as before.
• One fetcher, created before the start. startRemoteConfiguration(configuration, lifeCycle) becomes createRemoteConfiguration(configuration), which sends nothing on creation. preStartRum subscribes to its answers, then issues the first request; startRum connects it to the lifecycle (connectRemoteConfiguration). Still one request per page load.
• Consent. Consent withdrawn before RUM starts cancels the wait and stops the fetcher, so no retry goes out; a later grant starts afresh. The pre-start consent subscription is now kept until right before RUM starts, which also covers a withdrawal while waiting for the first startView with trackViewsManually.
• _dd.configuration.rc_wait. The wait (whole ms, at least 1) is kept with the draw it preceded (DrawnConfiguration.wait, persisted in the draw record even when the draw landed on the init values) and reported by every page of that session, next to rc_version.
• Settings stored before the start. When the session manager starts and storage holds a settings version different from the one the current session was drawn under, it judges that session by them once (endSessionIfSettingsAreDecisive). A session the page only continued — from another subdomain, or drawn before the settings changed — is ended by an emergency stop or a stricter privacy level, as it would be if the settings had arrived a moment later.
• Docs of remoteConfigurationEnabled and BeforeSamplingContext updated accordingly.

Trade-offs worth a look:

• Up to 1 s of start delay for pages with nothing stored. Uncaught errors and console errors raised during the wait are not collected (as before init); API calls are buffered; performance entries are recovered through buffered observers; the initial view still starts at navigation start.
• A page continuing a running session on an origin with nothing stored waits once as well (storage alone decides).
• A session drawn on the init values after a timeout is judged once per later page while the stored version differs from its draw, which calls beforeSampling once more on those pages.

Test instructions

• yarn test:unit — new and updated specs in preStartRum.spec.ts, startRum.spec.ts, remoteConfiguration.spec.ts, rumSessionManager.spec.ts, sessionContext.spec.ts.
• Manually: enable remoteConfigurationEnabled, clear site data, load a page and check that beforeSampling receives the delivered rate on the first draw and that view events carry _dd.configuration.rc_wait; reload and check that no wait happens; delay the settings response past 1 s and check that the page starts on the init values with rc_wait ≈ 1000.

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.