The thread in the stack is the coroutine created inside 'prepare_lua_coroutine'
with the arguments: LUA_DIALOG "FDdialog" "run_node" "d" ...

A call to 'resume_lua_coroutine' happens after each line of the node code, maybe
to return from C code?

After adding "while (lua_isthread(L, -1)) L = lua_tothread(L, -1);" to 'run_lua'
the error changes to "attempt to yield across a C-call boundary".