исправить: закрыть ревью сквозной корреляции

crates/crank-observability/tests/correlation.rs

@@ -1,3 +1,4 @@
+use axum::http::{HeaderMap, HeaderValue};
 use crank_observability::RequestId;
 use uuid::Version;
 
@@ -40,3 +41,34 @@ fn rejects_values_over_the_shared_limit() {
         Some(Version::SortRand)
     );
 }
+
+#[test]
+fn resolves_exactly_one_header_value_and_rejects_ambiguous_values() {
+    let mut single = HeaderMap::new();
+    single.insert(
+        "x-request-id",
+        HeaderValue::from_static("opaque-request-id"),
+    );
+
+    assert_eq!(
+        RequestId::resolve_from_headers(&single).as_str(),
+        "opaque-request-id"
+    );
+
+    let mut ambiguous = HeaderMap::new();
+    ambiguous.append("x-request-id", HeaderValue::from_static("first-request-id"));
+    ambiguous.append(
+        "x-request-id",
+        HeaderValue::from_static("second-request-id"),
+    );
+
+    let generated = RequestId::resolve_from_headers(&ambiguous);
+    assert_ne!(generated.as_str(), "first-request-id");
+    assert_ne!(generated.as_str(), "second-request-id");
+    assert_eq!(
+        uuid::Uuid::parse_str(generated.as_str())
+            .expect("generated UUID")
+            .get_version(),
+        Some(Version::SortRand)
+    );
+}