Can we use the `opStack` for this? This is rough thinking, but it seems like we could have an "input-pending mode" and a "character-pending mode". In input-pending, we're just looking for an "vim-mode:input-complete" command. In character-pending, the next typed character is automatically pushed to the stack as a `CharacterInput` operation. It composes with the `t` or `f` command below it, and voila.