refactor: address code review feedback on trace-context implementation

Agent-Logs-Url: https://github.com/cl-sdk/io.github.cl-sdk.wst/sessions/162c32ae-54fc-4676-ba0c-5b96de44bf6a

Co-authored-by: diasbruno <362368+diasbruno@users.noreply.github.com>

Author: Copilot

t/trace-context-tests.lisp

@@ -160,12 +160,11 @@
                       (trace-context-parent-id child))))))
 
 (test child-trace-context-inherits-tracestate-from-parent
-  (let* ((parent (parse-traceparent
-                  "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01"))
-         (_ (setf (trace-context-tracestate parent) "vendor=abc"))
-         (child (child-trace-context parent)))
-    (declare (ignore _))
-    (is (string= "vendor=abc" (trace-context-tracestate child)))))
+  (let ((parent (parse-traceparent
+                 "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01")))
+    (setf (trace-context-tracestate parent) "vendor=abc")
+    (let ((child (child-trace-context parent)))
+      (is (string= "vendor=abc" (trace-context-tracestate child))))))
 
 (test child-trace-context-overrides-tracestate-when-provided
   (let* ((parent (parse-traceparent

trace-context/package.lisp

@@ -2,6 +2,7 @@
   (:use #:cl)
   (:export
    #:trace-context
+   #:make-trace-context
    #:trace-context-version
    #:trace-context-trace-id
    #:trace-context-parent-id
@@ -138,9 +139,7 @@ PARENT-CTX. Pass NIL explicitly to suppress tracestate propagation."
                       :trace-id (trace-context-trace-id parent-ctx)
                       :parent-id (make-span-id)
                       :trace-flags (trace-context-trace-flags parent-ctx)
-                      :tracestate (if tracestate
-                                      tracestate
-                                      (trace-context-tracestate parent-ctx))))
+                      :tracestate (or tracestate (trace-context-tracestate parent-ctx))))
 
 (defun traceparent-string (ctx)
   "Serialize CTX to a traceparent header value string.

trace-context/routing.lisp

@@ -45,8 +45,7 @@ Returns REQUEST (mutated in place) for convenient use in middleware chains."
 
 Always includes :traceparent. Includes :tracestate when CTX carries a
 non-nil tracestate value."
-  (let ((headers (list :traceparent (traceparent-string ctx))))
-    (when (trace-context-tracestate ctx)
-      (setf headers (append headers
-                            (list :tracestate (trace-context-tracestate ctx)))))
-    headers))
+  (if (trace-context-tracestate ctx)
+      (list :traceparent (traceparent-string ctx)
+            :tracestate (trace-context-tracestate ctx))
+      (list :traceparent (traceparent-string ctx))))