Fixes a hidden-parent solo replay that could silence the mix. Also closes the N-mode segment silent no-op, amends the invariant comment, trims view.cpp under 600 lines, hedges two SDK inferences, drops a dead null-check.
Solo is cached, cleared and replayed per mode on a real switch only; the switch is refused visibly while the transport runs. The footer segment now routes through the activate actions, so a panel switch finally persists.
Top toolbar = capture+placement, bottom toolbar = Design-View verbs, footer = narrow Arrange|Design toggle + count + Tail button + set-apart Prune. New pure footer_bar module; Tail is now a real kit button.
daniel