Add user warnings for file truncation and size limits

- Alert user when file exceeds 1MB (rejected)
- Warn in filename when file is truncated (>50KB)
- Show clear '[TRUNCATED]' marker in content
- Better error handling with user-facing messages

client/main.js

@@ -547,21 +547,38 @@ function autoResizeTextarea(e) {
 
 async function handleFileSelect(e) {
   const files = Array.from(e.target.files);
+  const MAX_FILE_SIZE = 50000; // 50KB text limit
   
   for (const file of files) {
     try {
+      // Check file size first
+      if (file.size > 1024 * 1024) { // 1MB
+        alert(`File "${file.name}" is too large (${(file.size / 1024 / 1024).toFixed(1)}MB). Maximum size is 1MB.`);
+        continue;
+      }
+      
       // Read file content
       const content = await readFileContent(file);
       
+      // Warn if content will be truncated
+      let finalContent = content;
+      let warning = '';
+      if (content.length > MAX_FILE_SIZE) {
+        warning = ` (truncated - file is ${Math.round(content.length / 1000)}KB, max ${MAX_FILE_SIZE / 1000}KB per file)`;
+        finalContent = content.substring(0, MAX_FILE_SIZE) + '\n\n... [TRUNCATED - file too large for context window]';
+      }
+      
       state.files.push({
         id: file.name + '-' + Date.now(),
-        name: file.name,
+        name: file.name + warning,
         type: file.type,
         size: file.size,
-        content: content
+        content: finalContent,
+        truncated: content.length > MAX_FILE_SIZE
       });
     } catch (err) {
       console.error('Failed to read file:', file.name, err);
+      alert(`Failed to read file "${file.name}": ${err.message}`);
     }
   }
   
@@ -573,7 +590,7 @@ function readFileContent(file) {
   return new Promise((resolve, reject) => {
     const reader = new FileReader();
     reader.onload = () => resolve(reader.result);
-    reader.onerror = reject;
+    reader.onerror = () => reject(new Error('Failed to read file'));
     reader.readAsText(file);
   });
 }
@@ -676,15 +693,10 @@ function buildMessageContent(text, files) {
   if (!files.length) return text;
   
   const fileContents = files.map(f => {
-    const maxLen = 50000; // Limit file content length
-    const content = f.content || '[File content not available]';
-    const truncated = content.length > maxLen 
-      ? content.substring(0, maxLen) + '\n... [truncated]' 
-      : content;
-    return `--- ${f.name} ---\n${truncated}\n--- end of ${f.name} ---`;
+    return `--- ${f.name.replace(/ \(truncated.*\)$/, '')} ---\n${f.content}\n--- end of file ---`;
   }).join('\n\n');
   
-  return `${text}\n\n${fileContents}`;
+  return `${text}\n\nAttached files:\n\n${fileContents}`;
 }
 
 function updateLastMessage(content) {