createStandaloneApplication opens its first globe, attaches the scene host and returns attachScene/detachScene: a switch hands the session off, parks the outgoing renderer and attaches the incoming one with its catalog to the parts the phases registered once. A failed candidate releases what it attached; the working engine attaches again on the same shell, voice, tools and stores. ?switch=legacy keeps the route that builds an application per engine for one release. scripts/qa-app-once.mjs now asserts identity, UI, tool and listener continuity, the rollback and the legacy route.
window.__gevSession names each session object by a stable instance id and counts applications, attachments and detaches. scripts/qa-app-once.mjs (report-only with --report for now) runs three round trips and a parked-renderer rollback on a keyless preview with paid map, model and voice endpoints blocked.
German Khokhlov