improve reasoning toggle tests and refactor model capability checks

src/services/modelService.js

@@ -1,4 +1,5 @@
 import {supportsReasoning} from "../../public/app/modelCapabilities.js";
+import {AttachmentError} from "./attachmentService.js";
 
 class ModelServiceError extends Error {
     constructor(code, message, status = 500) {
@@ -196,7 +197,7 @@ export function createModelService(config, overrides = {}) {
                     const response = await fetchImpl(`${config.modelApiBaseUrl}/chat`, {
                         method: "POST",
                         headers: {"Content-Type": "application/json"},
-                        body: JSON.stringify(buildRequestBody(model, messagesPayload, options.generation, options.reasoning)),
+                        body: JSON.stringify({...buildRequestBody(model, messagesPayload, options.generation, options.reasoning), ...(options.format ? {format: options.format} : {})}),
                         signal
                     });
 
@@ -332,6 +333,7 @@ export function createModelService(config, overrides = {}) {
             };
         },
         mapError(error) {
+            if (error instanceof AttachmentError) return {status: error.status, body: {error: error.message}};
             if (error instanceof ModelServiceError) {
                 return {status: error.status, body: {error: error.message, code: error.code}};
             }