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Marc-André Bombeck
84d78d2926
Every entry in the display-transform registry declares the decimals its unit is read at. That number was carried to the render layer and read by exactly one screen out of all the ones that show a converted value, so everywhere else the raw product of a kilogram and 2.20462262185 reached the surface. Pounds came out with a dozen digits it never needed. Move the rounding into `applyDisplayTransform` and `applyDisplayTransformDelta`, so a surface gets a correctly-scaled number whether or not it remembers to ask. Patching the weight cell would have left the same trap behind inches, Fahrenheit, miles per hour and miles. Two boundaries stay exempt and are documented as such. A transform that does not rescale is the exact identity and is never rounded, so a stored 78.45 kg keeps rendering as 78.45 on the metric branch and every untransformed metric is byte-identical. `invertDisplayTransform` — the entry boundary — keeps full precision, because a value rounded on the way out and inverted on the way back would drift the stored canonical number a little further on every save; the entry surfaces quantise to their own two-decimal canonical dialect instead. `applyDisplayTransformUnrounded` is the one documented escape hatch, for arithmetic whose result is not rendered. The target adapter needs it: its guardrails round inward, and rounding the 30 kg floor to the nearest tenth of a pound first gives an edge that inverts to 29.98 kg and the server rejects it. The weight page and the HealthKit scaffold were folding the factor into their stat strips by hand. Both now convert through the helper, so the raw multiplier is only ever handed to the chart, which owns its own series and formatting. Formatting is unchanged. Precision is fixed at the conversion and the surfaces keep the formatter they already used, so switching preference changes the unit and nothing else about how the number looks. Refs #627