Add internal/tracing: env-gated OTel setup, span/log helpers, decorators

Co-Authored-By: Claude <noreply@anthropic.com>

internal/tracing/transport_test.go

@@ -0,0 +1,73 @@
+package tracing
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+	"go.opentelemetry.io/otel/sdk/trace/tracetest"
+	"go.opentelemetry.io/otel/trace"
+)
+
+func TestRestConfigWrapper_parentGated(t *testing.T) {
+	t.Parallel()
+
+	var gotTraceparent string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotTraceparent = r.Header.Get("traceparent")
+		w.WriteHeader(http.StatusOK)
+	}))
+	t.Cleanup(srv.Close)
+
+	sr := tracetest.NewSpanRecorder()
+	tp := sdktrace.NewTracerProvider(sdktrace.WithSpanProcessor(sr))
+	t.Cleanup(func() { _ = tp.Shutdown(context.Background()) })
+
+	rt := RestConfigWrapper(WithTracerProvider(tp))(http.DefaultTransport)
+	do := func(ctx context.Context) {
+		t.Helper()
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, srv.URL, nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+		resp, err := rt.RoundTrip(req)
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, _ = io.Copy(io.Discard, resp.Body)
+		_ = resp.Body.Close()
+	}
+
+	// No parent span: informer watches, leader election. Must not trace.
+	do(context.Background())
+	if len(sr.Ended()) != 0 {
+		t.Fatalf("request without parent span produced %d spans, want 0", len(sr.Ended()))
+	}
+	if gotTraceparent != "" {
+		t.Fatalf("request without parent span injected traceparent %q", gotTraceparent)
+	}
+
+	// Under a parent span: one client child span, traceparent injected.
+	ctx, parent := tp.Tracer("test").Start(context.Background(), "reconcile")
+	do(ctx)
+	parent.End()
+
+	var client sdktrace.ReadOnlySpan
+	for _, s := range sr.Ended() {
+		if s.SpanKind() == trace.SpanKindClient {
+			client = s
+		}
+	}
+	if client == nil {
+		t.Fatalf("no client span recorded, got %d spans", len(sr.Ended()))
+	}
+	if got := client.Parent().SpanID(); got != parent.SpanContext().SpanID() {
+		t.Errorf("client span parent = %s, want %s", got, parent.SpanContext().SpanID())
+	}
+	if gotTraceparent == "" {
+		t.Error("traceparent header not injected under a parent span")
+	}
+}