fix: SSE stream endpoint with proper HTTP/2 stream handling and heartbeat

- Fixed /api/stream/requests endpoint HTTP/2 INTERNAL_ERROR
- Use reply.raw.writeHead() instead of Fastify headers API for SSE
- Added 30s heartbeat to keep connection alive
- Proper event format with 'event:' and 'data:' fields
- Comprehensive error handling and cleanup on disconnect
- Mirrors working pattern from /api/stream/costs endpoint
- Resolves dashboard perpetual 'Loading...' state

packages/gateway/src/routes/dashboard.ts

@@ -463,31 +463,82 @@ export async function dashboardRoute(fastify: FastifyInstance): Promise<void> {
 
   // Server-Sent Events endpoint for real-time request updates
   fastify.get('/api/stream/requests', async (request: FastifyRequest, reply: FastifyReply) => {
-    // Set SSE headers
+    // Use raw Node.js API to properly initialize HTTP/2 stream
-    reply.type('text/event-stream');
+    reply.raw.writeHead(200, {
-    reply.header('Cache-Control', 'no-cache');
+      'Content-Type': 'text/event-stream',
-    reply.header('Connection', 'keep-alive');
+      'Cache-Control': 'no-cache',
+      'Connection': 'keep-alive',
+      'Access-Control-Allow-Origin': '*',
+      'Access-Control-Allow-Methods': 'GET',
+      'Access-Control-Allow-Headers': 'Content-Type',
+    });
+
+    const clientIp = request.ip;
+    const clientId = `${clientIp}-${Date.now()}`;
+
+    logger.info({ clientId, clientIp, activeListeners: globalRequestStream.getListenerCount() }, 'SSE client connected to /api/stream/requests');
 
     // Send initial connection message
-    reply.raw.write(`data: ${JSON.stringify({ type: 'connected', timestamp: new Date().toISOString() })}\n\n`);
+    reply.raw.write('event: connected\n');
+    reply.raw.write(`data: ${JSON.stringify({ clientId, timestamp: new Date().toISOString() })}\n\n`);
 
     // Subscribe to request events
     const unsubscribe = globalRequestStream.onRequest((event) => {
-      reply.raw.write(`data: ${JSON.stringify(event)}\n\n`);
+      try {
+        reply.raw.write('event: request-update\n');
+        reply.raw.write(`data: ${JSON.stringify(event)}\n\n`);
+      } catch (err) {
+        logger.debug({ clientId, err }, 'Error writing to SSE stream /api/stream/requests');
+        unsubscribe();
+        if (!reply.raw.writableEnded) {
+          reply.raw.end();
+        }
+      }
     });
 
+    // Keep connection alive with heartbeat every 30 seconds
+    const heartbeat = setInterval(() => {
+      try {
+        if (reply.raw.writable) {
+          reply.raw.write(': heartbeat\n\n');
+        } else {
+          clearInterval(heartbeat);
+          unsubscribe();
+        }
+      } catch (err) {
+        logger.debug({ clientId, err }, 'Heartbeat failed on /api/stream/requests');
+        clearInterval(heartbeat);
+        unsubscribe();
+      }
+    }, 30000);
+
     // Handle client disconnect
     reply.raw.on('close', () => {
+      logger.info({ clientId }, 'SSE client disconnected from /api/stream/requests');
+      clearInterval(heartbeat);
       unsubscribe();
-      logger.info('SSE client disconnected from /api/stream/requests');
     });
 
+    // Handle stream errors
     reply.raw.on('error', (error) => {
-      logger.error({ error }, 'SSE stream error');
+      logger.error({ clientId, error }, 'SSE stream error on /api/stream/requests');
+      clearInterval(heartbeat);
       unsubscribe();
     });
 
-    logger.info(`SSE client connected to /api/stream/requests (active: ${globalRequestStream.getListenerCount()})`);
+    // Cleanup on reply finish
+    reply.raw.on('finish', () => {
+      logger.debug({ clientId }, 'SSE stream finished on /api/stream/requests');
+      clearInterval(heartbeat);
+      unsubscribe();
+    });
+
+    // Prevent response from ending automatically
+    request.raw.on('close', () => {
+      logger.debug({ clientId }, 'Request closed on /api/stream/requests');
+      clearInterval(heartbeat);
+      unsubscribe();
+    });
   });
 
   // Test endpoint