sensord hung off graphical-session.target, which nothing on this device
starts, so it was enabled and dead from every boot. Down starts from a
last-seen stamp and structurally cannot see that. Bind the reporter to
sessiond and make the machine say so.
blueline-proximity-lock is 113 lines of shell implementing a subtle contract
(heartbeat inside SOURCE_DOWN_AFTER, seed from the probe banner, report both
edges) that would have been hand-copied for light and again for accel. One
binary, one contract, shipped in the package instead of the rootfs overlay.
