fix: properly chain gRPC interceptors and fix dashboard uptime

Two critical fixes for metrics:

1. Fix interceptor chaining
   - Changed from mixed grpc.UnaryInterceptor/ChainUnaryInterceptor to
     proper chaining with grpc.ChainUnaryInterceptor
   - Metrics interceptor now runs first (as intended)
   - All interceptors properly chained in order: metrics → auth → ratelimit
   - This fixes metrics not being recorded for any requests

2. Fix dashboard uptime calculation
   - Changed from page load time to process_start_time_seconds metric
   - Uptime now persists correctly across page refreshes
   - Uses Prometheus standard process_start_time_seconds gauge

Before: Metrics showed 0 for all requests, uptime reset on refresh
After: Metrics properly record all gRPC requests, uptime shows actual relay uptime

2 files changed, 32 insertions, 25 deletions

diff --git a/cmd/relay/main.go b/cmd/relay/main.go
index bd50e63..457a719 100644
--- a/cmd/relay/main.go
+++ b/cmd/relay/main.go
@@ -54,7 +54,18 @@ func main() {
         path, handler := nostrv1connect.NewNostrRelayHandler(connectHandler, connect.WithInterceptors())
         mux.Handle(path, handler)
 
-        var serverOpts []grpc.ServerOption
+        var unaryInterceptors []grpc.UnaryServerInterceptor
+        var streamInterceptors []grpc.StreamServerInterceptor
+
+        var m *metrics.Metrics
+        if cfg.Metrics.Enabled {
+                m = metrics.New(cfg.Metrics.ToMetrics())
+                unaryInterceptors = append(unaryInterceptors, metrics.UnaryServerInterceptor(m))
+                streamInterceptors = append(streamInterceptors, metrics.StreamServerInterceptor(m))
+
+                mux.Handle("/metrics", m.PrometheusHandler())
+                mux.Handle("/dashboard", m.DashboardHandler())
+        }
 
         if cfg.Auth.Read.Enabled || cfg.Auth.Write.Enabled {
                 authOpts := &auth.InterceptorOptions{
@@ -63,30 +74,22 @@ func main() {
                         TimestampWindow: cfg.Auth.TimestampWindow,
                         SkipMethods:     cfg.Auth.SkipMethods,
                 }
-                serverOpts = append(serverOpts,
-                        grpc.UnaryInterceptor(auth.NostrUnaryInterceptor(authOpts)),
-                        grpc.StreamInterceptor(auth.NostrStreamInterceptor(authOpts)),
-                )
+                unaryInterceptors = append(unaryInterceptors, auth.NostrUnaryInterceptor(authOpts))
+                streamInterceptors = append(streamInterceptors, auth.NostrStreamInterceptor(authOpts))
         }
 
         if cfg.RateLimit.Enabled {
                 limiter := ratelimit.New(cfg.RateLimit.ToRateLimiter())
-                serverOpts = append(serverOpts,
-                        grpc.ChainUnaryInterceptor(ratelimit.UnaryInterceptor(limiter)),
-                        grpc.ChainStreamInterceptor(ratelimit.StreamInterceptor(limiter)),
-                )
+                unaryInterceptors = append(unaryInterceptors, ratelimit.UnaryInterceptor(limiter))
+                streamInterceptors = append(streamInterceptors, ratelimit.StreamInterceptor(limiter))
         }
 
-        var m *metrics.Metrics
-        if cfg.Metrics.Enabled {
-                m = metrics.New(cfg.Metrics.ToMetrics())
-                serverOpts = append(serverOpts,
-                        grpc.ChainUnaryInterceptor(metrics.UnaryServerInterceptor(m)),
-                        grpc.ChainStreamInterceptor(metrics.StreamServerInterceptor(m)),
-                )
-
-                mux.Handle("/metrics", m.PrometheusHandler())
-                mux.Handle("/dashboard", m.DashboardHandler())
+        var serverOpts []grpc.ServerOption
+        if len(unaryInterceptors) > 0 {
+                serverOpts = append(serverOpts, grpc.ChainUnaryInterceptor(unaryInterceptors...))
+        }
+        if len(streamInterceptors) > 0 {
+                serverOpts = append(serverOpts, grpc.ChainStreamInterceptor(streamInterceptors...))
         }
 
         wsHandler := wshandler.NewHandler(store, subManager)
diff --git a/internal/metrics/dashboard.html b/internal/metrics/dashboard.html
index 800b6df..e7af48c 100644
--- a/internal/metrics/dashboard.html
+++ b/internal/metrics/dashboard.html
@@ -189,7 +189,7 @@
     </div>
 
     <script>
-        let startTime = Date.now();
+        let processStartTime = null;
 
         function parsePrometheusMetrics(text) {
             const metrics = {};
@@ -294,8 +294,15 @@
                 document.getElementById('event_deletions').textContent =
                     sumMetric(metrics, `${prefix}_relay_event_deletions_total`);
 
-                document.getElementById('uptime').textContent =
-                    formatUptime(Date.now() - startTime);
+                const processStart = sumMetric(metrics, 'process_start_time_seconds');
+                if (processStart > 0) {
+                    if (!processStartTime) processStartTime = processStart;
+                    const uptimeSeconds = Date.now() / 1000 - processStart;
+                    document.getElementById('uptime').textContent =
+                        formatUptime(uptimeSeconds * 1000);
+                } else {
+                    document.getElementById('uptime').textContent = '--';
+                }
 
                 document.getElementById('error').innerHTML = '';
             } catch (error) {
@@ -306,9 +313,6 @@
 
         updateMetrics();
         setInterval(updateMetrics, 5000);
-        setInterval(() => {
-            document.getElementById('uptime').textContent = formatUptime(Date.now() - startTime);
-        }, 1000);
     </script>
 </body>
 </html>