Context passed to the *cngxStepIndicator template. Drives the
numbered / checkmark / error glyph inside each step button. The
<button> shell - aria-current, aria-controls, click handler -
stays library-owned.
status mirrors node.state(). busy is the presenter-derived
"this step is the in-flight commit target" flag - independent of
status === 'pending' (which is the aggregate landmark state).