Add fail-fast on init for missing provider credentials

internal/observability/tracing_middleware.go

@@ -72,14 +72,29 @@ func TracingMiddleware(next http.Handler, tp *sdktrace.TracerProvider) http.Hand
 // statusResponseWriter wraps http.ResponseWriter to capture the status code.
 type statusResponseWriter struct {
 	http.ResponseWriter
-	statusCode int
+	statusCode  int
+	wroteHeader bool
 }
 
 func (w *statusResponseWriter) WriteHeader(statusCode int) {
+	if w.wroteHeader {
+		return
+	}
+	w.wroteHeader = true
 	w.statusCode = statusCode
 	w.ResponseWriter.WriteHeader(statusCode)
 }
 
 func (w *statusResponseWriter) Write(b []byte) (int, error) {
+	if !w.wroteHeader {
+		w.wroteHeader = true
+		w.statusCode = http.StatusOK
+	}
 	return w.ResponseWriter.Write(b)
 }
+
+func (w *statusResponseWriter) Flush() {
+	if flusher, ok := w.ResponseWriter.(http.Flusher); ok {
+		flusher.Flush()
+	}
+}