Function parse_todo_buffer 

pub fn parse_todo_buffer(
    text: &str,
    done_exists: bool,
    comment_char: char,
    resolve: &mut dyn FnMut(&str) -> TodoOidLookup,
) -> (Vec<RebaseTodoItem>, TodoParseMessages)

Parse the instruction sheet (todo_list_parse_insn_buffer + parse_insn_line). resolve maps an object-name token to a commit. Returns the items plus the ordered error/hint lines; an empty error list means the sheet parsed cleanly. Items that failed to parse are recorded as comments so totals/offsets still line up with upstream.