¡Ok, no puedo esperar! Probé con graphql-mesh.
Entonces, el archivo OpenAPI bajo el botón de descarga en https://docs.discourse.org/ parece estar roto 
Probé la validez aquí con este resultado:
Swagger schema validation failed.
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/3
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/3
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/3
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/2
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/2
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/2
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/1
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/1
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/1
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/0
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/0
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/0
JSON_OBJECT_VALIDATION_FAILED
Error: Swagger schema validation failed.
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/3
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/3
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/3
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/2
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/2
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/2
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/1
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/1
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/1
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/0
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/0
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/0
JSON_OBJECT_VALIDATION_FAILED
at o (https://apitools.dev/swagger-parser/online/js/bundle.min.js:1:73766)
at https://apitools.dev/swagger-parser/online/js/bundle.min.js:17:227596
SyntaxError: Swagger schema validation failed.
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/3
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/3
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/3
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/2
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/2
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/2
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/1
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/1
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/1
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/0
Data does not match any schemas from 'oneOf' at #/paths//page_view_total_reqs/get/parameters/0
Missing required property: schema at #/
Missing required property: content at #/
Missing required property: $ref at #/paths//page_view_total_reqs/get/parameters/0
JSON_OBJECT_VALIDATION_FAILED
at Function.o [as syntax] (https://apitools.dev/swagger-parser/online/js/bundle.min.js:1:73766)
at validateSchema (https://apitools.dev/swagger-parser/online/js/bundle.min.js:1:5021)
at SwaggerParser.validate (https://apitools.dev/swagger-parser/online/js/bundle.min.js:1:3171)
z-schema validation error: JSON_OBJECT_VALIDATION_FAILED
at ZSchema.getLastError (https://apitools.dev/swagger-parser/online/js/bundle.min.js:17:211187)
at validateSchema (https://apitools.dev/swagger-parser/online/js/bundle.min.js:1:4925)
at SwaggerParser.validate (https://apitools.dev/swagger-parser/online/js/bundle.min.js:1:3171)
Así que busqué otro archivo OpenAPI o Swagger de la API de Discourse. Solo encontré este.
Está un poco roto en la línea 426, pero lo arreglé.
Después de configurar graphql-mesh, ¡obtuve una API GraphQL funcional! Pero…
Este archivo Swagger no está completo o es demasiado antiguo. Solo hay 4 consultas, ninguna mutación, el tipo user con pocas propiedades…
¿Existe en algún lugar un archivo Swagger u OpenAPI de Discourse?