/// Parse a first-line slash command of the form `/name <rest>`./// Returns `(name, rest_after_name, rest_offset)` if the line begins with `/`/// and contains a non-empty name; otherwise returns `None`.////// `rest_offset` is the byte index into the original line where `rest_after_name`/// starts after trimming leading whitespace (so `line[rest_offset..] == rest_after_name`).pub fn parse_slash_name(line: &str) -> Option<(&str, &str, usize)> {    let stripped = line.strip_prefix('/')?;    let mut name_end_in_stripped = stripped.len();    for (idx, ch) in stripped.char_indices() {        if ch.is_whitespace() {            name_end_in_stripped = idx;            break;        }    }    let name = &stripped[..name_end_in_stripped];    if name.is_empty() {        return None;    }    let rest_untrimmed = &stripped[name_end_in_stripped..];    let rest = rest_untrimmed.trim_start();    let rest_start_in_stripped = name_end_in_stripped + (rest_untrimmed.len() - rest.len());    let rest_offset = rest_start_in_stripped + 1;    Some((name, rest, rest_offset))}