[p1c2u]

Problem

OpenAPI 3.0 schemas are checked against the JSON Schema Draft 4 metaschema. The OAS 3.0 Schema Object is a restricted subset of Wright Draft 00, and JSON Schema keywords it does not list are unsupported (OAS 3.0.3). Draft 4 still accepts type arrays, definitions, id, $schema, patternProperties, const, items arrays and unknown keywords, so invalid 3.0 schemas pass check_schema.

Change

• Vendor the official OAS 3.0 schema (2024-10-18) unmodified under schemas/oas3.0/schema/. The specifications registry picks it up automatically, and it ships in the wheel.
• check_schema for OAS 3.0 uses the official Schema, Reference, Discriminator, XML and ExternalDocumentation definitions. This applies to OAS30Validator and the Strict, Read and Write variants; the variants previously fell back to jsonschema's default Draft 4 check.
• The official oneOf: [Schema, Reference] alternatives are rewritten at import time to choose by the presence of $ref, as the specification does. Errors therefore name the offending keyword (['string', 'null'] is not of type 'string', 'definitions' does not match any of the regexes: '^x-') rather than a generic oneOf failure. Keys next to $ref are ignored.
• META_SCHEMA and instance validation are unchanged.
• No docs changes; the migration note below is meant for the 0.10 release notes.

Breaking change

• Schemas that use keywords OpenAPI 3.0 doesn't support now raise SchemaError.
• So does a root carrying non-Schema Object keys, such as components, or a whole OpenAPI document passed to validate().

To migrate, provide referenced schemas via registry=..., validate fragments through a validator built from the full document, or skip the check with check_schema=False. This needs a minor version bump (0.10).

Not covered, to stay faithful to the official schema: "items MUST be present if type is array" is not enforced.

Overlaps with #306, which also changes OAS 3.0 schema checking; whichever merges second will need a rebase.

Checks

• 332 passed, 6 skipped (55 new tests in tests/unit/test_oas30_schema_object_metaschema.py)
• mypy: only the 2 _regex.py errors that already exist on master
• black, isort, flynt, pyupgrade, deptry and the Sphinx -n -W build all clean