[xidedix]

Body scroll lock and modal-open are held per owner and released when the hide transitions end, not when the backdrop goes. The backdrop is one element per type, removed after its own fade and brought back while fading, so switching modals no longer flashes 0.5 → 0 → 0.5. No timers: the end comes from the element's running CSS transitions (getAnimations), or a microtask when nothing transitions (reduced motion, transition=false, jsdom, server).

Behaviour changes:

• Offcanvas: backdrop off/on keeps the lock; scroll applies while open. Without a backdrop, padding-left stayed on body after closing in RTL; with one, the service timer used to remove it.
• Modal: modal-open kept while another modal holds it, removed on destroy; under reduced motion display: none and portal detached at once (was display: block); with transition=false the backdrop shows and goes without a fade; a modal closed during a server render leaves a clean body; a modal that never opened keeps its own display.
• Offcanvas: the host becomes inert only once the hide ends, its content still at close: a click on the sliding panel lands on the panel instead of passing through to the fading backdrop, the panel's controls stay inactive and the host takes no focus; the host has tabindex only while open or laid out in place. Responsive offcanvas laid out in place stays without inert. Modal keeps inert at close.
• Backdrop goes after its own fade (~150 ms, was a 300 ms timer), so from then a click outside the closing offcanvas panel or over the transparent closing modal reaches the page.
• BackdropService: new lockScroll(owner)/unlockScroll(owner); hideScrollbar()/resetScrollbar() deprecated, they lock on behalf of the service, so an outside resetScrollbar() no longer releases a component lock and clearBackdrop() no longer touches the lock. unlockScroll() removes the padding side the lock set; the page's own inline padding on that side is overwritten while locked and not restored, as before. scrollbarWidth is measured when the first owner locks, not on setBackdrop(). setBackdrop() returns the shared element of its type, pair it with clearBackdrop(); new optional fade argument. A backdrop released before its delayed show no longer flashes, one set again before it waits for it instead of popping in, and closing and reopening a modal in one tick keeps one backdrop.
• ModalService: addOpenClass(modal)/removeOpenClass(modal).
• OffcanvasModule, ModalModule: services no longer in providers, a lazy module or a routed standalone component gets the root instances: one backdrop and one backdropClick$ per page, and opened$ and id toggles reach modals across the former module boundary.

Offcanvas specs run the component in a test host, no hosts or backdrops left in the shared document.