openapi: raw preservation routes numbers through float64, corrupting extensions and preserved keywords

[OmarAlJarrah]

Summary

nodeToRaw decodes a YAML node into any and re-marshals it as JSON. yaml.v3 decodes out-of-int64 integers and all decimals into float64, so every path that promises verbatim preservation silently rounds numbers:

• x-* extensions (extensionsFrom),
• oneOf/anyOf sibling preservation,
• the §4.7 carve-out (not/if-then-else/dependentSchemas/contains/unevaluated*),
• tuple items-after-prefix.

This defeats exactly the documented "preserved verbatim in Extensions" guarantee. #23 fixed the Value/BigVal channel; the raw-preservation channel has the same class of bug.

Reproduction

openapi: 3.1.0
info: {title: t, version: '1'}
paths: {}
components:
  schemas:
    S:
      type: object
      x-big: 12345678901234567890123
      x-frac: 1.000000000000000000001

Result: Extensions["openapi:x-big"] == 1.2345678901234568e+22, Extensions["openapi:x-frac"] == 1.

Root cause

compilers/openapi/schema.go:866-881 — node.Decode(&any) + json.Marshal instead of a number-preserving conversion.

Expected

Raw preservation must be number-safe: either serialize from the yaml.Node tree directly (rendering scalar numbers from their source text) or decode with a number-preserving representation (e.g. json.Number semantics). "Preserved verbatim" should mean byte-faithful for every scalar the source can express.