Enforce at least two files selected for merge

frontend/src/components/tools/shared/FileStatusIndicator.tsx

@@ -5,17 +5,19 @@ import { useTranslation } from "react-i18next";
 export interface FileStatusIndicatorProps {
   selectedFiles?: File[];
   placeholder?: string;
+  minFiles?: number;
 }
 
 const FileStatusIndicator = ({
   selectedFiles = [],
   placeholder,
+  minFiles = 1,
 }: FileStatusIndicatorProps) => {
 const { t } = useTranslation();
   const defaultPlaceholder = placeholder || t("files.placeholder", "Select a PDF file in the main view to get started");
 
   // Only show content when no files are selected
-  if (selectedFiles.length === 0) {
+  if (selectedFiles.length < minFiles) {
     return (
       <Text size="sm" c="dimmed">
         {defaultPlaceholder}

frontend/src/components/tools/shared/FilesToolStep.tsx

@@ -7,6 +7,7 @@ export interface FilesToolStepProps {
   isCollapsed?: boolean;
   onCollapsedClick?: () => void;
   placeholder?: string;
+  minFiles?: number;
 }
 
 export function createFilesToolStep(
@@ -23,6 +24,7 @@ export function createFilesToolStep(
     <FileStatusIndicator
       selectedFiles={props.selectedFiles}
       placeholder={props.placeholder || t("files.placeholder", "Select a PDF file in the main view to get started")}
+      minFiles={props.minFiles}
     />
   ));
 }

frontend/src/components/tools/shared/createToolFlow.tsx

@@ -8,6 +8,7 @@ export interface FilesStepConfig {
   selectedFiles: File[];
   isCollapsed?: boolean;
   placeholder?: string;
+  minFiles?: number;
   onCollapsedClick?: () => void;
   isVisible?: boolean;
 }
@@ -68,6 +69,7 @@ export function createToolFlow(config: ToolFlowConfig) {
           selectedFiles: config.files.selectedFiles,
           isCollapsed: config.files.isCollapsed,
           placeholder: config.files.placeholder,
+          minFiles: config.files.minFiles,
           onCollapsedClick: config.files.onCollapsedClick
         })}
 

frontend/src/tools/Merge.tsx

@@ -75,7 +75,8 @@ const Merge = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
     }) as any /* FIX ME: Parameter type is wrong on setSelectedFiles */);
   }, []);
 
-  const hasFiles = selectedFiles.length > 1; // Merge requires at least 2 files
+  const minFiles = 2; // Merging one file doesn't make sense
+  const hasFiles = selectedFiles.length >= minFiles;
   const hasResults = mergeOperation.files.length > 0 || mergeOperation.downloadUrl !== null;
   const settingsCollapsed = !hasFiles || hasResults;
 
@@ -84,6 +85,7 @@ const Merge = ({ onPreviewFile, onComplete, onError }: BaseToolProps) => {
       selectedFiles,
       isCollapsed: hasFiles && !hasResults,
       placeholder: "Select multiple PDF files to merge",
+      minFiles: minFiles,
     },
     steps: [
       {