fix: unique addPage ids + collision-free scopeId hashing

M-3: PageContext.addPage minted ids from bare `page_${Date.now()}` --
two adds inside the same millisecond collided on id, so a subsequent
rename/delete/save silently acted on both pages at once. Added a
module-scoped monotonic counter combined with the timestamp
(nextPageId(), exported for direct unit testing) and used it
everywhere an addPage-style id is minted (addPage, replaceAllPages).

M-4: scopeId() lowercased + stripped non-alphanumeric characters from
the node id into a slug, so two node ids differing only by
case/punctuation (e.g. "AbC" vs "abc", or "a-b" vs "ab") collapsed
onto the same scope -- defeating the whole point of scoping ids per
node (M-1/Menu/Tabs/ColumnLayout/Gallery/etc. all rely on it). Now
hashes the raw node id via the existing djb2 stableHash() instead of
slugifying it: still deterministic (same id -> same scope) and a valid
CSS ident, but collision-resistant across case/punctuation. This
changes the exact scope strings Menu/Tabs/ColumnLayout/Gallery/etc.
emit -- expected and fine, since none of their tests pinned an exact
scope value (all already asserted structure/uniqueness).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/state/PageContext.tsx

@@ -43,6 +43,20 @@ interface PageContextValue {
 const HEADER_ID = '__header__';
 const FOOTER_ID = '__footer__';
 
+// M-3: `page_${Date.now()}` alone collides when two pages are minted inside
+// the same millisecond (addPage called twice in quick succession, or two AI
+// replaceAllPages entries) -- then rename/delete/save operate on both pages
+// at once since they share an id. A module-scoped monotonic counter,
+// combined with the timestamp, guarantees uniqueness regardless of how many
+// ids are minted within the same millisecond. This is state/id-minting code
+// (not toHtml/export), so Date.now() here is fine -- see task-minors-brief.md.
+let pageIdCounter = 0;
+
+/** Mints a unique page id: timestamp (base36) + a monotonic per-process counter (base36). */
+export function nextPageId(): string {
+  return 'page_' + Date.now().toString(36) + '_' + (++pageIdCounter).toString(36);
+}
+
 const EMPTY_CANVAS =
   '{"ROOT":{"type":{"resolvedName":"Container"},"isCanvas":true,"props":{"style":{"minHeight":"100vh","backgroundColor":"#ffffff"},"tag":"div"},"displayName":"Container","custom":{},"hidden":false,"nodes":[],"linkedNodes":{}}}';
 
@@ -338,7 +352,7 @@ export const PageProvider: React.FC<{ children: ReactNode }> = ({ children }) =>
   const addPage = useCallback(
     (name: string, slug: string) => {
       const requestedSlug = slug || slugify(name);
-      const id = `page_${Date.now()}`;
+      const id = nextPageId();
 
       // Save current page first
       saveCurrentState();
@@ -452,7 +466,7 @@ export const PageProvider: React.FC<{ children: ReactNode }> = ({ children }) =>
       const slug = i === 0 ? 'index' : uniqueSlug(slugify(p.name), seenSlugs);
       seenSlugs.push(slug);
       return {
-        id: i === 0 ? 'home' : `page_${Date.now()}_${i}`,
+        id: i === 0 ? 'home' : nextPageId(),
         name: p.name,
         slug,
         craftState: treeToCraftState(p.tree),