fix: harden typed metrics review findings

crates/crank-core/src/correlation.rs

@@ -183,6 +183,11 @@ impl TraceContext {
         &self.traceparent
     }
 
+    /// Whether this context was selected for recording by the upstream/local sampler.
+    pub fn is_sampled(&self) -> bool {
+        self.traceparent.ends_with("-01")
+    }
+
     pub fn tracestate_within_budget(value: &str) -> bool {
         header_list_within_budget(
             value,

crates/crank-core/tests/correlation.rs

@@ -55,6 +55,8 @@ fn traceparent_parser_is_strict_and_never_accepts_zero_ids() {
         "0af7651916cd43dd8448eb211c80319c"
     );
     assert_eq!(context.traceparent(), VALID_TRACEPARENT);
+    assert!(context.is_sampled());
+    assert!(!TraceContext::generate().is_sampled());
 
     for invalid in [
         "00-00000000000000000000000000000000-b7ad6b7169203331-01",