mesh/merge-gate pass: builds new: modules/sensors, sent nowhere; no bus step; every machine composes with the change as it did without (4 of 4 compose)
Temperatures against the hardware's own thresholds, fans, each drive's health and the kernel's error
counts, read-only. A root watch reads SMART so the tools need no root and never wake a sleeping drive;
smartd and the watch carry the health that raises a condition when the hardware says it is failing.
