Composed-tree shadow DOM capture, sized invisible spacers, track re-anchoring, block fill-width slides, javascript: href sanitization

- Walker serializes the composed (flattened) tree: open shadow roots walk
  as host children with <slot> replaced by its assigned light nodes (or
  fallback), so custom-element content (product cards, web components) is
  captured instead of arriving childless
- In-flow visibility:hidden nodes with a nonzero border box survive the
  prune as sized invisible placeholders - ghost spacers carry load-bearing
  geometry
- When pruning drops leading in-flow children of a horizontally-translated
  track, the baked translateX is re-anchored by their aggregate margin-box
  width (settled carousel tracks return to origin instead of pushing real
  content off-screen); animation-owned transforms unaffected
- Circular-shrink slide guard counts block-level fill children as
  width-deriving regardless of wAuto (block auto-width IS fill), pinning
  library-sized slide widths uniformly
- javascript: hrefs emit as "#" and the link gate normalizes both sides

382 tests pass (18 new), typecheck clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

compiler/src/validate/gates.ts

@@ -313,8 +313,12 @@ function isValidRetag(srcTag: string, genTag: string): boolean {
   return genTag === "div" && /^(ul|ol|menu|dl|p|h[1-6])$/.test(srcTag); // content-model → div
 }
 
-function normHref(href: string, origin: string): string {
+export function normHref(href: string, origin: string): string {
   if (!href) return "";
+  // A `javascript:*` href is a script trigger, not a navigable URL. Generation emits an inert `#`
+  // for it (React blocks the literal), so treat every javascript: href — on either side — as `#`
+  // and let the two sides match instead of failing on the un-reproducible script string.
+  if (/^\s*javascript:/i.test(href)) return "#";
   if (href.startsWith("#")) return href;
   try {
     const u = new URL(href, origin);