Remove custom response handler from Merge (#4457)

# Description of Changes
Remove custom response handler from Merge. Also make `filePrefix`
mandatory for `multiFile` tools to make the output more visually
different since you get a new 'V1' file rather than 'V2' of the current
file.

CLAUDE.md

@@ -89,7 +89,6 @@ return useToolOperation({
   endpoint: '/api/v1/misc/compress-pdf',
   buildFormData: (params, file: File) => { /* single file */ },
   multiFileEndpoint: false,
-  filePrefix: 'compressed_'
 });
 ```
 
@@ -103,7 +102,7 @@ return useToolOperation({
   endpoint: '/api/v1/general/split-pages',
   buildFormData: (params, files: File[]) => { /* all files */ },
   multiFileEndpoint: true,
-  filePrefix: 'split_'
+  filePrefix: 'split_',
 });
 ```
 
@@ -115,7 +114,6 @@ return useToolOperation({
 return useToolOperation({
   operationType: 'convert',
   customProcessor: async (params, files) => { /* custom logic */ },
-  filePrefix: 'converted_'
 });
 ```
 

frontend/src/hooks/tools/merge/useMergeOperation.test.ts

@@ -81,24 +81,6 @@ describe('useMergeOperation', () => {
     expect(formData.get('generateToc')).toBe('false');
   });
 
-  test('should handle response correctly', () => {
-    renderHook(() => useMergeOperation());
-
-    const config = getToolConfig();
-    const mockBlob = new Blob(['merged content'], { type: 'application/pdf' });
-    const mockFiles = [
-      new File(['content1'], 'file1.pdf', { type: 'application/pdf' }),
-      new File(['content2'], 'file2.pdf', { type: 'application/pdf' })
-    ];
-
-    const result = config.responseHandler!(mockBlob, mockFiles) as File[];
-
-    expect(result).toHaveLength(1);
-    expect(result[0].name).toBe('merged_file1.pdf');
-    expect(result[0].type).toBe('application/pdf');
-    expect(result[0].size).toBe(mockBlob.size);
-  });
-
   test('should return the hook result from useToolOperation', () => {
     const { result } = renderHook(() => useMergeOperation());
 

frontend/src/hooks/tools/merge/useMergeOperation.ts

@@ -1,5 +1,5 @@
 import { useTranslation } from 'react-i18next';
-import { useToolOperation, ResponseHandler, ToolOperationConfig, ToolType } from '../shared/useToolOperation';
+import { useToolOperation, ToolOperationConfig, ToolType } from '../shared/useToolOperation';
 import { createStandardErrorHandler } from '../../../utils/toolErrorHandler';
 import { MergeParameters } from './useMergeParameters';
 
@@ -16,11 +16,6 @@ const buildFormData = (parameters: MergeParameters, files: File[]): FormData =>
   return formData;
 };
 
-const mergeResponseHandler: ResponseHandler = (blob: Blob, originalFiles: File[]): File[] => {
-  const filename = `merged_${originalFiles[0].name}`
-  return [new File([blob], filename, { type: 'application/pdf' })];
-};
-
 // Operation configuration for automation
 export const mergeOperationConfig: ToolOperationConfig<MergeParameters> = {
   toolType: ToolType.multiFile,
@@ -28,7 +23,6 @@ export const mergeOperationConfig: ToolOperationConfig<MergeParameters> = {
   operationType: 'merge',
   endpoint: '/api/v1/general/merge-pdfs',
   filePrefix: 'merged_',
-  responseHandler: mergeResponseHandler,
 };
 
 export const useMergeOperation = () => {

frontend/src/hooks/tools/shared/useToolOperation.ts

@@ -31,7 +31,10 @@ interface BaseToolOperationConfig<TParams> {
   /** Operation identifier for tracking and logging */
   operationType: string;
 
-  /** Prefix added to processed filenames (e.g., 'compressed_', 'split_') */
+  /**
+   * Prefix added to processed filenames (e.g., 'compressed_', 'split_').
+   * Only generally useful for multiFile interfaces.
+   */
   filePrefix?: string;
 
   /**
@@ -68,6 +71,9 @@ export interface MultiFileToolOperationConfig<TParams> extends BaseToolOperation
   /** This tool processes multiple files at once. */
   toolType: ToolType.multiFile;
 
+  /** Prefix added to processed filename (e.g., 'merged_', 'split_') */
+  filePrefix: string;
+
   /** Builds FormData for API request. */
   buildFormData: ((params: TParams, files: File[]) => FormData);
 
@@ -214,9 +220,9 @@ export const useToolOperation = <TParams>(
             processedFiles = await config.responseHandler(response.data, filesForAPI);
           } else if (response.data.type === 'application/pdf' ||
                     (response.headers && response.headers['content-type'] === 'application/pdf')) {
-            // Single PDF response (e.g. split with merge option) - use original filename
+            // Single PDF response (e.g. split with merge option) - add prefix to first original filename
-            const originalFileName = filesForAPI[0]?.name || 'document.pdf';
+            const filename = `${config.filePrefix}${filesForAPI[0]?.name || 'document.pdf'}`;
-            const singleFile = new File([response.data], originalFileName, { type: 'application/pdf' });
+            const singleFile = new File([response.data], filename, { type: 'application/pdf' });
             processedFiles = [singleFile];
           } else {
             // Default: assume ZIP response for multi-file endpoints