The loadModule_ primitive now returns NULL for already-loaded modules and an error string for missing modules, shifting the error handling from Wren's Fiber.abort to C's native string return. The Wren import_ method simplifies to only call the result when non-null, removing the false/true branching logic.
The Wren scripts in this directory get converted to C string literals and then inserted into their respective .c files so that the interpreter can load them directly without having to do any file IO.
The script that does this copying is script/generate_builtins.py.
You can invoke using make builtin.