--- a/ui/server/toolkit.c	Thu May 28 17:45:20 2026 +0200
+++ b/ui/server/toolkit.c	Thu May 28 18:07:00 2026 +0200
@@ -52,6 +52,9 @@
 static CxMap *srv_obj_map;
 static uint64_t srv_obj_id_counter = 0;
 
+// NOOP on most platforms, expect macos
+void ui_set_main_thread_error_msg(const char *msg) {}
+
 void ui_init(const char *appname, int argc, char **argv) {
     ui_app_name = appname ? strdup(appname) : NULL;