VTERM_MOD_ALT
vterm_push_output_sprintf(vt, mod & VTERM_MOD_ALT ? "\e%c" : "%c", k.literal);
if(needs_CSIu && (mod & ~VTERM_MOD_ALT)) {
vterm_push_output_sprintf(vt, "%s%c", mod & VTERM_MOD_ALT ? "\e" : "", c);