- rootUnion: keywords the two declarations state SEPARATELY can contradict too.
A merged `const` is now checked against its own `type` and `enum`, so
root `x: { type: "string" }` under branch `x: { const: 1 }` declines
instead of seeding an immutable 1 into a string field. An integer const still
satisfies a `number` type — the one direction JSON Schema widens.
- TUI missingRequiredFields tests `Object.hasOwn` first: an argument legally
named `constructor` resolved to the inherited one and read as supplied, and
the call went out without it.
Signed-off-by: cliffhall <cliff@futurescale.com>