Third recurrence of the stale-mount bug: the ExecStartPre cleanup ran on clean ground and the portal still came up mountless, sitting active while every fresh flatpak sandbox failed to build. Add an ExecStartPost that polls for the fuse mount and fails the start after five seconds without one, so a mountless portal shows up failed in the journal and the next bus activation retries from the cleanup instead of lingering broken. Claude-Session: https://claude.ai/code/session_01CTL7G5u3iDf1NCM6rTyCES