Body measurements are stored metric and shown in the person's units

Weight and height are logged as dated body measurements, stored in kilograms and centimetres whatever the person's unit system, and converted only when shown or typed. Each log entry is its own row and is added or corrected, never merged, so a chart is a plain read of the log and switching between metric and imperial changes nothing stored. The profile's other fields (birthdate, pronouns, sex assigned at birth) are single values, not a log; age is computed from the birthdate and never stored.

Consequences

• Conversion and rounding (kg to lb, cm to ft and in, with the half-inch the input allows) live in shared Kotlin with tests, like every decision about data; the apps only render.
• Distances and speeds already follow the unit system the same way; this makes body measurements one more case, not a second mechanism.
• A new SQLDelight migration adds the measurement table. No existing table changes, so existing phones lose nothing and no backward-compatibility code is needed.
• Entries are append-only and per day, in the spirit of ADR 0003 and ADR 0006: when sync arrives, two phones' entries both survive.
• The profile stays on the phone, guest-only, until an account exists; nothing here sends it anywhere.