#126139 deleted guest-onboarding-flag.test.ts ahead of the guided-onboarding rewrite, which also took the only coverage of desktopBackendSpawnEnv — the assertion #118114 added for the stay-alive stamp included. Restore a focused test file: the launch-decision stamping invariants plus the unconditional GATEWAY_ON_ALL_ADAPTERS_DOWN=stay_alive stamp (#118080).