pub fn register_narrow_operator(registry: &mut CommandRegistry) -> OperatorIdExpand description
N.1.3 (2026-06-10): register the zn narrow operator into the
grammar’s CommandRegistry and return its OperatorId.
The operator is universal — you narrow from any editable buffer,
like d / y / c. Per the mode-ownership split, this crate owns
the operator SPEC + apply; the host wires the zn chord to the
returned OperatorId at the universal operator-pending layer
(operator-pending composition needs the host-resolved Builtins,
which this crate can’t reach). The narrow-VIEW surface
(:widen / :w / q) stays with NarrowMode.
apply reads the resolved OperatorContext.range (the span the
following motion / text object produced), converts it to an
inclusive whole-line span, and emits
Effect::AppAction(AppEffect::NarrowLines { .. }); the host arm
narrows the active buffer to that span via create_narrow_view.