Read const when building a body from a schema

[MathiasWP]

"$.scope does not match any allowed schema" — from an API validating against the same document Fiber built the body from.

The field

"scope": { "anyOf": [
  { "type": "string", "const": "once" },
  { "type": "string", "const": "always" }
]}

skeleton checks example, default and enum, then falls through to the choice, takes the first branch, finds nothing to go on there either, and prints the string placeholder — for a field whose only two legal values are named right there.

Why it matters more than one field

const is JSON Schema 2020-12, which is what OpenAPI 3.1 uses. A literal union written as anyOf of consts is what 3.1 generators emit where 3.0 would have written an enum.

The spec this was found on has 543 consts and zero enums across 658 paths — so the enum branch that already existed never fired once, and every literal field in that API came out as a placeholder that could only ever be rejected.

Fix

const is taken as the value it names, alongside example and default, in skeleton and in example_string (so a form field pinned to one value arrives holding it rather than empty).

Verified against the real 720 KB spec before and after — /agent/deny-tool-call now yields:

{
  "agentId": string,
  "seq": integer,
  "part": integer,
  "partIndex": integer,
  "scope": "once"
}

Placeholders still show what to type where the schema genuinely doesn't say; only the values the document states outright are filled in.

Testing

cargo fmt --check, cargo clippy --no-default-features --all-targets -- -D warnings, cargo test (134 passed, 1 new covering a choice-of-consts, a bare const, and placeholders still appearing for everything else), pnpm check (0 errors), pnpm test:e2e (316 passed).