Addressed feedback from kwilczynski, thank you!

internal/server/request_start_middleware.go

@@ -6,6 +6,10 @@ import (
 	"time"
 )
 
+const (
+	requestStartHeader = "X-Request-Start"
+)
+
 type RequestStartMiddleware struct {
 	next http.Handler
 }
@@ -17,13 +21,8 @@ func WithRequestStartMiddleware(next http.Handler) http.Handler {
 }
 
 func (h *RequestStartMiddleware) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	if r.Header.Get("X-Request-Start") == "" {
-		r.Header.Set("X-Request-Start", h.nowStr())
+	if r.Header.Get(requestStartHeader) == "" {
+		r.Header.Set(requestStartHeader, strconv.FormatInt(time.Now().UnixMilli(), 10))
 	}
 	h.next.ServeHTTP(w, r)
 }
-
-func (h *RequestStartMiddleware) nowStr() string {
-	var now = time.Now().UnixMilli()
-	return strconv.FormatInt(now, 10)
-}

internal/server/request_start_middleware_test.go

@@ -10,8 +10,8 @@ import (
 
 func TestRequestStartMiddleware_AddsUnixMilliWhenNotPresent(t *testing.T) {
 	handler := WithRequestStartMiddleware(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		id := r.Header.Get("X-Request-Start")
-		assert.NotEmpty(t, id)
+		timestamp := r.Header.Get(requestStartHeader)
+		assert.NotEmpty(t, timestamp)
 	}))
 
 	r := httptest.NewRequest("GET", "/", nil)
@@ -23,13 +23,13 @@ func TestRequestStartMiddleware_AddsUnixMilliWhenNotPresent(t *testing.T) {
 
 func TestRequestStartMiddleware_PreservesExistingHeaderWhenPresent(t *testing.T) {
 	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		id := r.Header.Get("X-Request-Start")
-		assert.Equal(t, "1234", id)
+		timestamp := r.Header.Get(requestStartHeader)
+		assert.Equal(t, "1234", timestamp)
 	})
 	handler := WithRequestStartMiddleware(next)
 
 	r := httptest.NewRequest("GET", "/", nil)
-	r.Header.Set("X-Request-Start", "1234")
+	r.Header.Set(requestStartHeader, "1234")
 
 	w := httptest.NewRecorder()
 	handler.ServeHTTP(w, r)

internal/server/server.go

@@ -119,11 +119,12 @@ func (s *Server) startCommandHandler() error {
 func (s *Server) buildHandler() http.Handler {
 	var handler http.Handler
 
+	// Note: handlers are executed in the inverse order.
 	handler = s.router
-	handler = WithRequestStartMiddleware(handler)
 	handler, _ = WithErrorPageMiddleware(pages.DefaultErrorPages, true, handler)
 	handler = WithLoggingMiddleware(slog.Default(), s.config.HttpPort, s.config.HttpsPort, handler)
 	handler = WithRequestIDMiddleware(handler)
+	handler = WithRequestStartMiddleware(handler)
 
 	return handler
 }