Sweep every feet + inches pair the fields can offer and every whole-inch
height across the canonical range, asserting the value comes back
unchanged and lands inside the server's window. Assert the metric branch
with toBe so a re-derivation of a stored height cannot slip through.
Render both entry surfaces under each preference: the metric case keeps
the single centimetres box with the canonical guardrails, the imperial
case shows the feet + inches pair seeded from the stored value. Extend
the structural guard so a surface that drops the adapter, hardcodes a
centimetre guardrail, or hardcodes a unit label trips a tripwire.
