multipart/form-data controllers lack @RequestPart binding and consumes declaration

[joseegman-idoneea]

Description

For a multipart/form-data request body, the generated Spring controller interface is not usable as-is:

1. No @RequestPart / @RequestParam binding annotation. The whole multipart body is collapsed into a single generated wrapper DTO passed as a bare @Valid parameter (the only effect of the form-data branch is that @RequestBody is omitted). Spring cannot bind multipart parts this way.
2. No consumes declaration. The @RequestMapping hard-codes produces = {"application/json"} and never advertises consumes = MediaType.MULTIPART_FORM_DATA_VALUE, even though the operation's consumes list is already computed.
3. The wrapper DTO is immutable. It is generated as an immutable Lombok @Value type (builder only, no no-arg constructor / setters), so even Spring's default @ModelAttribute binding cannot instantiate it at runtime.

Steps to reproduce

paths:
  /test:
    post:
      operationId: testMultipart
      requestBody:
        required: true
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                someString:
                  type: string
                someFile:
                  type: string
                  format: binary

Actual result

@RequestMapping(method = RequestMethod.POST, value = "/test", produces = {"application/json"})
default ResponseEntity<Void> testMultipart(@Valid InlineObjectTestMultipart inlineObjectTestMultipart) { ... }

No @RequestPart, no consumes, and InlineObjectTestMultipart is an immutable @Value class.

Expected result

Each multipart part exposed as its own @RequestPart, files as MultipartFile / List<MultipartFile>, plus a consumes declaration:

@RequestMapping(method = RequestMethod.POST, value = "/test",
    produces = {"application/json"},
    consumes = {MediaType.MULTIPART_FORM_DATA_VALUE})
default ResponseEntity<Void> testMultipart(
    @RequestPart(value = "someString", required = false) String someString,
    @RequestPart(value = "someFile", required = false) MultipartFile someFile) { ... }

Root cause

templates/openapi/template.ftlh only uses the isFormData flag to drop @RequestBody; it never emits @RequestPart/consumes. OpenApiUtil.processRequestBody registers the multipart schema as a wrapper model regardless.

Environment

• Affects the OpenAPI code generator (multiapi-engine), Spring server interface template.
• Reproduced on main.