Fix: Resolve 'Link Severed' race condition by preventing double-termination of streams and improving error handling

backend/controllers/ai.js

@@ -181,6 +181,7 @@ exports.chat = asyncHandler(async (req, res, next) => {
         }
       } catch (e) { console.error("Gradio Error", e); }
       
+      if (res.writableEnded) return;
       await Message.create({ sessionId: session._id, sender: 'user', content: message || "[SIGNAL]", attachmentUrl });
       await Message.create({ sessionId: session._id, sender: 'ai', content: fullAIResponse || "[EMPTY_SIGNAL]", modelUsed: activeModelName });
       user.usage.requestsToday += 1;
@@ -248,13 +249,15 @@ exports.chat = asyncHandler(async (req, res, next) => {
     console.log(`[DEBUG] Calling API: ${apiUrl} for model: ${apiModelId}`);    const response = await axios.post(apiUrl, { model: apiModelId, messages: apiMessages, stream: true, temperature: 0.7 }, { headers: { 'Authorization': `Bearer ${apiKey}`, 'Content-Type': 'application/json' }, responseType: 'stream' });
 
     let fullAIResponse = "";
+    let isStreamEnded = false;
+
     response.data.on('data', chunk => {
       const lines = chunk.toString().split('\n');
       for (const line of lines) {
         if (line.startsWith('data: ')) {
-          const dataStr = line.slice(6);
+          const dataStr = line.slice(6).trim();
           if (dataStr === '[DONE]') {
-            res.write(`data: ${JSON.stringify({ done: true, sessionId: session._id })}\n\n`);
+            isStreamEnded = true;
             return;
           }
           try {
@@ -270,6 +273,7 @@ exports.chat = asyncHandler(async (req, res, next) => {
     });
 
     response.data.on('end', async () => {
+      if (res.writableEnded) return;
       await Message.create({ sessionId: session._id, sender: 'user', content: message || "[SIGNAL]", attachmentUrl });
       await Message.create({ sessionId: session._id, sender: 'ai', content: fullAIResponse, modelUsed: activeModelName });
       user.usage.requestsToday += 1;
@@ -278,11 +282,21 @@ exports.chat = asyncHandler(async (req, res, next) => {
       res.end();
     });
 
+    response.data.on('error', (err) => {
+      console.error("Stream Error:", err);
+      if (!res.writableEnded) {
+        res.write(`data: ${JSON.stringify({ error: "STREAM_ERROR", details: err.message })}\n\n`);
+        res.end();
+      }
+    });
+
   } catch (err) {
     console.error("[DEBUG] Chat Controller Catch:", err.message);
-    res.write(`data: ${JSON.stringify({ error: "NEURAL_LINK_SEVERED", details: err.message })}\n\n`);
-    res.write(`data: ${JSON.stringify({ done: true })}\n\n`);
-    res.end();
+    if (!res.writableEnded) {
+      res.write(`data: ${JSON.stringify({ error: "NEURAL_LINK_SEVERED", details: err.message })}\n\n`);
+      res.write(`data: ${JSON.stringify({ done: true })}\n\n`);
+      res.end();
+    }
   }
 });
 

backend/public/chat.html

@@ -397,6 +397,12 @@
                         if (line.startsWith('data: ')) {
                             try {
                                 const data = JSON.parse(line.slice(6));
+                                if (data.error) {
+                                    aiNode.querySelector('.prose').innerHTML += `<div class="text-red-500 font-bold mt-2">!! ${data.error}: ${data.details || ''}</div>`;
+                                    isProcessing = false;
+                                    clearTimeout(safetyTimeout);
+                                    return;
+                                }
                                 if (data.message) { 
                                     fullText += data.message; 
                                     aiNode.querySelector('.prose').innerHTML = marked.parse(fullText);