fix(observability): prevent otel reactor panic in non-tokio contexts

tests/otel_dependency_feature_regression.rs

@@ -0,0 +1,17 @@
+#[test]
+fn opentelemetry_otlp_uses_blocking_reqwest_client() {
+    let manifest = include_str!("../Cargo.toml");
+    let otlp_line = manifest
+        .lines()
+        .find(|line| line.trim_start().starts_with("opentelemetry-otlp ="))
+        .expect("Cargo.toml must define opentelemetry-otlp dependency");
+
+    assert!(
+        otlp_line.contains("\"reqwest-blocking-client\""),
+        "opentelemetry-otlp must include reqwest-blocking-client to avoid Tokio reactor panics"
+    );
+    assert!(
+        !otlp_line.contains("\"reqwest-client\""),
+        "opentelemetry-otlp must not include async reqwest-client in this runtime mode"
+    );
+}