vecnode/dsh-modal

Modal: the pack's shared dialog surface for the vncode Web GUI. A body-level overlay any client plugin reaches through ctx.get('modals') - open/alert/confirm/prompt, with async submit work that keeps the dialog open and shows the failure inline - plus a RICH dialog (spec.content plus size: 'lg'), a render function handed { close } that owns the whole body for a dialog that is not a question, whose mask click deliberately does not close it. Alpha.