Reactive (WebFlux) controllers have no multipart/form-data handling

[joseegman-idoneea]

Description

The reactive (WebFlux) server interface template (templateReactive.ftlh) has no handling for multipart/form-data request bodies. It wraps the request body in Mono<...> / Flux<...> with @Valid @RequestBody and references the wrapper DTO, so a multipart upload:

1. has no @RequestPart binding and no consumes declaration, and
2. would use the wrapper DTO / MultipartFile, which is a Servlet type not supported by WebFlux annotated controllers.

This is the reactive counterpart of the annotated-controller multipart issue (#388).

Steps to reproduce

Generate a reactive API (reactive: true) from a spec with a multipart/form-data body containing a file (type: string, format: binary) and a file array.

Expected result

Each part exposed as @RequestPart, files typed with the WebFlux FilePart API, plus a consumes declaration:

@RequestMapping(method = RequestMethod.POST, value = "/upload",
    produces = {"application/json"},
    consumes = {MediaType.MULTIPART_FORM_DATA_VALUE})
default ResponseEntity<Void> uploadMultipart(
    @RequestPart(value = "someFile", required = false) FilePart someFile,
    @RequestPart(value = "someFiles", required = false) Flux<FilePart> someFiles,
    @RequestPart(value = "someString", required = false) String someString,
    @ApiIgnore final ServerWebExchange exchange) { ... }

Root cause

templateReactive.ftlh never branches on request.isFormData; both signature variants (with/without securities) always emit @RequestBody wrapped in Mono/Flux.

Environment

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