fix: listen on response close event instead of request close

The req.on('close') event fires when the request body is fully received,
not when the client disconnects. This was causing all requests to be
aborted immediately after parsing the body.

Changed to res.on('close') which properly fires only when the client
actually disconnects before the response is complete.

Author: hletrd

src/server.ts

@@ -1465,8 +1465,8 @@ async function handleChatCompletions(req: IncomingMessage, res: ServerResponse):
     abortController.abort();
   }, REQUEST_TIMEOUT_MS);
 
-  // Handle client disconnect
-  req.on('close', () => {
+  // Handle client disconnect - listen on response socket, not request
+  res.on('close', () => {
     if (!res.writableEnded) {
       structuredLog('info', 'Request', 'Client disconnected', { requestId });
       abortController.abort();