another tweak

cmd/server/main.go

@@ -328,7 +328,8 @@ func buildDiagramsNetURL(r *http.Request, id string) string {
 		scheme = "https"
 	}
 	base := fmt.Sprintf("%s://%s/diagram?id=%s", scheme, r.Host, url.QueryEscape(id))
-	return "https://app.diagrams.net/?splash=0&ui=min&url=" + url.QueryEscape(base)
+	// Request AWS library for custom shapes (e.g., aws4) to render correctly.
+	return "https://app.diagrams.net/?splash=0&ui=min&libs=aws4&url=" + url.QueryEscape(base)
 }
 
 func addCORS(w http.ResponseWriter) {