Function nova_rt_fs_last_error_message 

#[unsafe(no_mangle)]
pub extern "C" fn nova_rt_fs_last_error_message() -> *mut NovaStr

Take the pending error message.

The fs_ prefix is now historical, for the same reason nova_rt_fs_take_bytes’s doc comment gives: [fail] stashes into the same per-task [Slot::Message] regardless of which module’s intrinsic called it. Every fallible wrapper in std/io/lib.nova – read_stdin, write_stdout, write_stderr, flush_stdout and flush_stderr – reads its own error message back through this same taker now, alongside std/fs’s own wrappers.