- rootUnion: the added-names guard is now a shared `addsForbiddenNames` and
applies to the `allOf` fold as well as to union branches. A member adding a
name a restrictive root `additionalProperties` rejects would otherwise be
merged beside the keyword, where the name reads as allowed.
- selectBranchIndex tests `Object.hasOwn` before reading a pinned value: a
field legally named `constructor` resolved to the inherited one and ruled
out the very branch that pins it.
Signed-off-by: cliffhall <cliff@futurescale.com>