Description

Using @hey-api/openapi-ts v0.85.2, request bodies that reference a schema containing writeOnly fields are generated with the read-only shape instead of the writable shape. The generator correctly emits both Payload and PayloadWritable, but CreateItemRequest keeps pointing at Payload, so the required writeOnly property (encoded in the repro) disappears from the type you’re supposed to send to the API.

That leaves the writable helper unused and causes TS2353 (“Object literal may only specify known properties”) whenever you try to supply the required field:

const req: CreateItemRequest = {
  payload: { kind: 'jpeg', encoded: 'YmFy' },
                        // ^^^^^^^ Property 'encoded' is missing in type 'Payload'
};

I’d expect request payloads (operation body types) to reference the writable variant so that writeOnly properties remain available when constructing the request.

Reproducible example or configuration

npx --yes @hey-api/openapi-ts \
--input writeonly-repro.yml \
--output out \
--plugins @hey-api/typescript

Generated snippet (out/types.gen.ts):

export type CreateItemRequest = {
    payload: Payload;
};

export type Payload = {
    kind: 'jpeg';
};

export type PayloadWritable = {
    kind: 'jpeg';
    /**
     * Data required on write
     */
    encoded: string;
};

OpenAPI specification (optional)

openapi: 3.0.3
info:
  title: writeOnly repro
  version: 1.0.0
paths:
  /items:
    post:
      operationId: item_create
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateItemRequest'
      responses:
        '201':
          description: Created
components:
  schemas:
    CreateItemRequest:
      type: object
      required:
        - payload
      properties:
        payload:
          $ref: '#/components/schemas/Payload'
    Payload:
      type: object
      required:
        - kind
        - encoded
      properties:
        kind:
          type: string
          enum: [jpeg]
        encoded:
          type: string
          writeOnly: true
          description: Data required on write

System information (optional)

@hey-api/openapi-ts 0.85.2
Node.js v23.7.0
macOS 15.7.1 (24G231)