OpenAPI spec validation error

Steps to reproduce

1. Create spec enhancer, which add custom extension to #/components/schemas

@injectable(asSpecEnhancer, { scope: BindingScope.SINGLETON })
export class ComponentsSpecEnhancer implements OASEnhancer {
  name = 'components';

  modifySpec(spec: OpenApiSpec): ValueOrPromise<OpenApiSpec> {
    const components: ComponentsObject = {
      schemas: {
        TupleArray: {
          title: 'TupleArray',
          type: 'array',
          items: {
            type: 'array',
            items: [{ type: 'number' }, { type: 'number' }],
            additionalItems: false,
          },
          example: [[4, 0.2]],
        },
      },
    };
    return mergeOpenAPISpec(spec, { components });
  }
}

2. Reference this scheme in route or controller description. In request body, for example.

@requestBody({
      required: true,
      content: {
        'application/json': {
          schema: {
            allOf: [
              getModelSchemaRef(Transaction),
              {
                type: 'object',
                properties: {
                  contribution: {
                    $ref: '#/components/schemas/TupleArray',
                  },
                },
                required: ['contribution'],
              },
            ],
          },
        },
      },
    })

3. Call this endpoint with correct request body

Current Behavior

Got error from AJV during validation at @loopback/rest/src/validation/request-body.validator.ts:157

[MissingRefError: can't resolve reference #/components/schemas/TupleArray from id #] {
  missingRef: '#/components/schemas/TupleArray',
  missingSchema: ''
}

Expected Behavior

Passed validation

Additional information

linux x64 14.15.1

├── @loopback/authentication@7.0.7
├── @loopback/boot@3.3.0
├── @loopback/context@3.15.1
├── @loopback/core@2.15.1
├── @loopback/logging@0.4.7
├── @loopback/openapi-v3@5.2.1
├── @loopback/repository-json-schema@3.3.1
├── @loopback/repository@3.5.1
├── @loopback/rest-explorer@3.2.0
├── @loopback/rest@9.2.1
├── @loopback/security@0.3.7
├── @loopback/service-proxy@3.1.0

The problem is that resolveControllerSpec at @loopback/openapi-v3/src/controller-spec.ts:71 skips extensions, referenced in api description if $ref doesn't have definitions at the same level (@loopback/openapi-v3/src/controller-spec.ts:493), which IMO, shouldn't happen.

Start with @loopback/rest/src/validation/request-body.validator.ts:157 and trace how the schema reaches AJV. Compare that flow with @loopback/openapi-v3/src/controller-spec.ts, especially resolveControllerSpec at line 71 and the referenced logic near line 493. Done means a request body using the custom components schema validates without a MissingRefError.