fix: use singleton pattern and force nodejs runtime for metrics route

- Add runtime = 'nodejs' to ensure Node.js environment
- Add dynamic = 'force-dynamic' to prevent static optimization
- Use singleton pattern to avoid duplicate metric registration
- Add error logging for debugging

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/api/metrics/route.ts

@@ -1,30 +1,55 @@
 import { NextResponse } from 'next/server';
 import client from 'prom-client';
 
-// Create a Registry to register the metrics
-const register = new client.Registry();
+// Force Node.js runtime for this route
+export const runtime = 'nodejs';
+export const dynamic = 'force-dynamic';
 
-// Add default metrics (CPU, memory, etc.)
-client.collectDefaultMetrics({ register });
+// Singleton pattern to avoid duplicate metric registration
+const globalForProm = globalThis as unknown as {
+  promRegistry: client.Registry | undefined;
+  metricsInitialized: boolean | undefined;
+};
 
-// Custom metrics
-const httpRequestsTotal = new client.Counter({
+function getRegistry(): client.Registry {
+  if (!globalForProm.promRegistry) {
+    globalForProm.promRegistry = new client.Registry();
+  }
+  return globalForProm.promRegistry;
+}
+
+function initializeMetrics(register: client.Registry) {
+  if (globalForProm.metricsInitialized) {
+    return;
+  }
+
+  // Add default metrics (CPU, memory, etc.)
+  client.collectDefaultMetrics({ register });
+
+  // Custom metrics
+  new client.Counter({
     name: 'http_requests_total',
     help: 'Total number of HTTP requests',
     labelNames: ['method', 'path', 'status'],
     registers: [register],
-});
+  });
 
-const httpRequestDuration = new client.Histogram({
+  new client.Histogram({
     name: 'http_request_duration_seconds',
     help: 'Duration of HTTP requests in seconds',
     labelNames: ['method', 'path'],
     buckets: [0.1, 0.3, 0.5, 0.7, 1, 3, 5, 7, 10],
     registers: [register],
-});
+  });
+
+  globalForProm.metricsInitialized = true;
+}
 
 export async function GET() {
   try {
+    const register = getRegistry();
+    initializeMetrics(register);
+
     const metrics = await register.metrics();
     return new NextResponse(metrics, {
       status: 200,
@@ -33,6 +58,7 @@ export async function GET() {
       },
     });
   } catch (error) {
+    console.error('Metrics error:', error);
     return NextResponse.json({ error: 'Failed to get metrics' }, { status: 500 });
   }
 }