The shell's scene part detaches it too, so a candidate failing in a later part (a layer's drawing, Cockpit clouds) leaves the shell free for the working engine instead of refusing every later attach. StyleManager.attachScene releases what it built when it throws, and one detach runs at a time. The controls phase awaits its parts, and a failed attachment no longer forces handoff off for the parts it releases. scripts/qa-app-once.mjs now also rolls back from a Navara candidate whose layer attachment fails.
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