fix(otel): cumulative metric temporality + metricIntervalMs knob (real metrics-export fix)

hive-c0re/src/meta.rs

@@ -668,6 +668,7 @@ struct OtelConfig {
     protocol: String,
     extra_resource_attributes: Option<String>,
     headers_credential: Option<String>,
+    metric_interval_ms: Option<u64>,
 }
 
 /// Read the hive-wide OTEL config from env, or `None` when OTEL is off.
@@ -690,11 +691,16 @@ fn otel_config() -> Option<OtelConfig> {
     let headers_credential = std::env::var("HYPERHIVE_OTEL_HEADERS_CREDENTIAL")
         .ok()
         .filter(|v| !v.is_empty());
+    let metric_interval_ms = std::env::var("HYPERHIVE_OTEL_METRIC_INTERVAL_MS")
+        .ok()
+        .and_then(|v| v.parse::<u64>().ok())
+        .filter(|v| *v > 0);
     Some(OtelConfig {
         endpoint,
         protocol,
         extra_resource_attributes,
         headers_credential,
+        metric_interval_ms,
     })
 }
 
@@ -982,6 +988,11 @@ where
                 esc(cred)
             );
         }
+        if let Some(ms) = otel.metric_interval_ms {
+            // Int option — emit a bare numeric literal (no quotes). `ms` is a
+            // parsed u64, so it can't inject anything into the rendered nix.
+            let _ = writeln!(out, "              hyperhive.otel.metricIntervalMs = {ms};");
+        }
     }
     out.push_str(
         r#"              # The harness service inside the container runs as a