A callback passed to a generic call without a return annotation can
return values the checker unifies into a narrower result type ('return
items' beside 'return items.map((i) => ({ ...i, extra }))' infers
Item[]). Converting the extended objects into that type copied them
and dropped the added members, which Node keeps and a later wider view
reads back. Such a return is now refused by name, pointing at the
annotation that keeps the members.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
