feat: add cpu_time_seconds Prometheus metric

bin/debug-trace-server/src/metrics.rs

@@ -163,6 +163,26 @@ impl ResponseSizeMetrics {
     }
 }
 
+/// CPU execution time per request (global, no method label).
+#[derive(Clone, Metrics)]
+#[metrics(scope = "debug_trace")]
+pub struct CpuTimeMetrics {
+    /// CPU execution time per request in seconds
+    cpu_time_seconds: Histogram,
+}
+
+impl CpuTimeMetrics {
+    /// Creates global CPU time metrics.
+    pub fn create() -> Self {
+        Self::new_with_labels(&[] as &[(&str, &str)])
+    }
+
+    /// Records a CPU time measurement.
+    pub fn record(&self, seconds: f64) {
+        self.cpu_time_seconds.record(seconds);
+    }
+}
+
 // ---------------------------------------------------------------------------
 // ── Cache Layer ────────────────────────────────
 // ---------------------------------------------------------------------------
@@ -427,6 +447,9 @@ fn pre_register_all_metrics() {
     let _ = ResponseSizeMetrics::new_for_method(METHOD_TRACE_BLOCK);
     let _ = ResponseSizeMetrics::new_for_method(METHOD_TRACE_TRANSACTION);
 
+    // Request Layer: CPU time (global)
+    let _ = CpuTimeMetrics::create();
+
     // Cache Layer
     let _ = CacheMetrics::new_for_cache(CACHE_TYPE_DEBUG_TRACE);
     let _ = CacheMetrics::new_for_cache(CACHE_TYPE_TRACE);

bin/debug-trace-server/src/timing.rs

@@ -17,6 +17,8 @@ use http::{HeaderName, HeaderValue};
 use pin_project_lite::pin_project;
 use tower::{Layer, Service};
 
+use crate::metrics::CpuTimeMetrics;
+
 /// Header name for execution time in nanoseconds.
 pub const TIMING_HEADER_NAME: &str = "x-execution-time-ns";
 
@@ -111,6 +113,8 @@ where
                         response.headers_mut().insert(header_name, header_value);
                     }
                 }
+                // Record as Prometheus metric
+                CpuTimeMetrics::create().record(Duration::from_nanos(cpu_ns).as_secs_f64());
                 Poll::Ready(Ok(response))
             }
             Poll::Ready(Err(e)) => Poll::Ready(Err(e)),