Goal

On full document navigations between layout screens, keep the sidebar and topbar visually stable so the page does not blank out as a whole. Navigation stays a normal same-origin page load: a new Wicket page, new Ajax callback URLs, and new WebSocket observers. This is not SPA-style content swapping.

Requirements

1. Enable cross-document view transitions for same-origin navigations (@view-transition { navigation: auto; }).
2. Pair chrome with CSS view-transition-name on the existing .sidebar and .topbar classes (already unique on LayoutPage). Do not add HTML ids for this, and do not use Wicket markup ids.
3. Honor prefers-reduced-motion: reduce by disabling the effect.
4. Unsupported browsers keep current behavior (progressive enhancement). Firefox does not ship cross-document view transitions yet; Chromium 126+ and Safari 18.2+ do.

Out of scope

• Fetch-and-swap or innerHTML replacement of #content / #main
• Click interception and History API as a router
• Server-side AbstractAjaxBehavior to render another page into the current one
• Naming .side-info or .main (those classes are duplicated or unstable and skip the whole transition)
• Changing intra-page Ajax + onedev.server.history.pushState (already same-document)

Constraints

• Only the chrome boxes are pinned. Sidebar menus and the topbar title still change across project, administration, user, and my pages.
• SimplePage (login and similar) has no sidebar or topbar.
• .sidebar and .topbar already use CSS transition: all … ease; that must not fight view-transition snapshots.
• Only real document navigations participate. Wicket Ajax updates, many window.location fallbacks, POSTs, and some redirects will not.

Acceptance criteria

•  Same-origin full navigations between LayoutPage screens in supporting browsers keep sidebar and topbar from blanking out with the rest of the document
•  No duplicate view-transition-name values (in particular, do not name .side-info or nested .main)
•  prefers-reduced-motion: reduce disables the effect
•  Unsupported browsers are unchanged
•  Existing intra-page Ajax navigation is unchanged