Coroutines are mostly working but they're kind of junk anyway. Feel free to tinker with this if you like.

builder.cpp

@@ -56,6 +56,8 @@ void Builder::run_build() {
   while(fgets(buffer, BUF_MAX, build_out) != nullptr) {
     string line(buffer);  // yeah, that's probably a problem
 
+    cerr << buffer;
+
     smatch err;
     bool match = regex_match(line, err, err_re);