pub fn apply(cfg: &mut Config, cmd: &Command) -> Result<Option<String>, String>Expand description
Apply the Config half of a command. Ok(Some(text)) is a
message for the status line (a query’s answer); Ok(None) is a
silent success, mutt-style. Commands the TUI owns (bind, macro,
alias, push, exec) return Ok(None) without touching the config,
so the caller must handle those itself.