/// Operator identity carried by the reducer. Kept independent of
/// `hjkl-engine` so `hjkl-vim` has no upstream dependency.
///
/// Only the five operators that can be entered directly from Normal mode via
/// bare `d` / `y` / `c` / `>` / `<` are listed here. Case operators
/// (`gu` / `gU` / `g~`) and Reflow (`gq`) are deferred to chunk 2c-v;
/// Fold (`zf`) does not enter bare op-pending so it is omitted entirely.