- anyOfAdmitsNull recognizes a branch that constrains nothing (`{}`, or
annotations only): it admits every value, null among them, so a field pinned
to `const: null` beside such a union stays submittable. `admitsNull`
cannot say that on its own — an unconstrained schema tells it nothing either
way and it declines rather than guesses — but here the question is narrower.
- convertToolParameters sends a matched `const` as the schema's own typed
value: `kind=2` selects a branch pinned to `const: 2` and was then sent
`"2"`, which that same branch rejects. Only an exact match is
substituted; anything else is the user's input and is left alone.
Signed-off-by: cliffhall <cliff@futurescale.com>