`const { a, ...rest } = options ?? {}` destructures the options record or
an empty object. Where the record had a required member, the `{}`
fallback was coerced into the record and failed with SC2002. The source
now lowers to the union of the record and the empty record, so the
union pattern lowering reads each key from the arm that holds it, the
empty arm answers undefined and the rest element packs nothing. A
record arm without a literal key now answers undefined in unionKeyGet
too, which the frontend already asked for and the validator rejected
as an internal error. All-optional options keep their lowering.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
