fields.number rounds stored values to 3 decimals: formatOptions is never forwarded to NumberField

What happens

fields.number silently rounds committed values to 3 decimal places. Typing 51.98600 stores 51.986. This makes the field unusable for latitude/longitude: 0.001° is ~111 m of latitude, so a map marker lands on the wrong block.

Reproduced on @keystatic/core@0.5.48; the relevant code is unchanged in 0.6.8.

Why

NumberFieldInput passes nine props to @keystar/ui's NumberField — label, description, isRequired, errorMessage, onBlur, autoFocus, step, value, onChange — and no formatOptions:

// dist/keystatic-core.js:2476 (0.5.48), :2455ff (0.6.8) — inside NumberFieldInput
jsx(NumberField, { label, description, isRequired, errorMessage, onBlur, autoFocus, step, value, onChange })

(Corrected 2026-08-25: this block first cited dist/index-b09c5e84.js:58 and an eight-prop list without step — that is IntegerFieldInput, a different component that also renders NumberField. See the correction comment below; the conclusion is unchanged.)

NumberField accepts formatOptions (@keystar/ui/src/number-field/types.tsx) and forwards its props to useNumberFieldState, whose commit() round-trips the value (not just the display text) through the formatter:

// @react-stately/numberfield
clampedValue = numberParser.parse(format(clampedValue));
setNumberValue(clampedValue);

With no formatOptions, format is an Intl.NumberFormat with the default maximumFractionDigits: 3. So the rounding is in the stored value, and it is locale-independent — that default is the same in every locale for style: 'decimal'.

Why step is not the workaround

NumberFieldInput does forward step to NumberField, but useNumberFieldState derives its NumberFormatter/NumberParser from formatOptions alone (useNumberFieldState.mjs:33-47), and snapValueToStep runs before the parse(format(...)) line above — so a step of 0.00001 is still rounded back to 3 decimals. formatOptions appears to be the only lever.

IntegerFieldInput omits formatOptions as well; harmless for integers, but both call sites would want the prop.

Suggested fix

Expose formatOptions?: Intl.NumberFormatOptions on fields.number and forward it to NumberField (a hoisted/memoized value, since useNumberFieldState compares formatOptions by identity and resets inputValue when it changes — an inline literal would clobber input while typing).

A narrower alternative would be to derive maximumFractionDigits from step when one is given, which would make the existing step option meaningful for the UI.

Happy to open a PR if you'd like it in either shape.

Context

Community platform for a Dutch municipality where non-technical editors enter organisation coordinates through the CMS. The editor reported it as "the field only accepts 3 decimals" — the field description we had written told them to enter 5.

Start with NumberFieldInput and IntegerFieldInput, then read @keystar/ui/src/number-field/types.tsx and the described useNumberFieldState formatting behavior. The change is complete when fields.number exposes and forwards formatOptions without disrupting typing, and committed values retain the requested decimal precision.