minorToDecimalString

Renders minor currency units (e.g. paise, cents) to a "<major>.<minor>" decimal string with fractionDigits digits — the single canonical minorUnits->decimal formatter for :common and its consumers.

Three call sites used to each roll their own: this file's formatDecimal used Double + HALF_UP, googlepay's provider used java.math.BigDecimal + HALF_EVEN, and upi-intent's provider used a raw Long divmod (amountMinor / 100, amountMinor % 100) that mis-formats negative amounts — e.g. -1050 minor units rendered as "-10.-50" instead of "-10.50", because Kotlin's % keeps the dividend's sign. Since minor units are already an exact integer count of the smallest currency unit there's no fractional precision to round away (the split is always exact); the part that must be unified is sign handling, following the same abs+negative-flag convention as formatDecimal so there is exactly one leading - and a magnitude-only fraction.