Surprising behavior with PlainYearMonth subtraction and constraining

[catamorphism]

(Initially discovered by @ptomato)

In the reference implementation, Temporal.PlainYearMonth.from({ year: 2024, monthCode: 'M02' }).subtract({ years: 1 }, { overflow: 'reject' }) throws:

Uncaught RangeError: value out of range: 1 <= 29 <= 28
    at RejectToRange (file:///home/tjc/proposal-temporal/polyfill/lib/ecmascript.mjs:2784:41)
    at RejectISODate (file:///home/tjc/proposal-temporal/polyfill/lib/ecmascript.mjs:2789:3)
    at Module.RegulateISODate (file:///home/tjc/proposal-temporal/polyfill/lib/ecmascript.mjs:697:7)
    at Object.dateAdd (file:///home/tjc/proposal-temporal/polyfill/lib/calendar.mjs:202:32)
    at CalendarDateAdd (file:///home/tjc/proposal-temporal/polyfill/lib/ecmascript.mjs:1713:46)
    at Module.AddDurationToYearMonth (file:///home/tjc/proposal-temporal/polyfill/lib/ecmascript.mjs:4144:21)
    at Temporal.PlainYearMonth.subtract (file:///home/tjc/proposal-temporal/polyfill/lib/plainyearmonth.mjs:96:15)

This behavior is consistent with the spec, because AddDurationToYearMonth constructs a full date from a YearMonth and passes it to CalendarDateAdd; the date's day is the last day of the same month (when subtracting). So in this case, the date 2024-02-29 is passed to CalendarDateAdd; because the overflow setting is reject, it's rejected because there is no 2023-02-29 in the ISO calendar.

This seems like it would be surprising to users. For YearMonth, overflow would be expected to apply to years and months, but not days, since there is no day visible to the user.

[ptomato]

Related snippet:

> Temporal.PlainYearMonth.from({ year: 1999, month: 2, day: 29 }, { overflow: 'reject' })
Temporal.PlainYearMonth <1999-02>

This also seems to be correct per the specification, but the behaviour is inconsistent with the snippet that Tim posted above.