Fix I-1: landing-page edits lost when activePageId goes dangling

buildSavePayload matched the active page by page.id === activePageId,
but activePageId defaults to the hardcoded 'home' and load() never
updated it. Deleting the original Home page (its replacement gets id
page_<ts>), reloading, editing, and saving would then match no page --
the live edit only reached the legacy top-level craft_state, while the
authoritative pages[]/pages_craft_state[0] for index.html fell back to
stale state.

Belt-and-suspenders fix:
- buildSavePayload now falls back to pages[0] as the effective active
  page when a real page is active but activePageId matches nothing.
- useWhpApi's load() now points activePageId at the freshly restored
  first page via a new PageContext setActivePageIdDirect setter
  (bookkeeping only -- no re-serialize/deserialize), so activePageId
  stays valid after every load.

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

craft/src/hooks/useWhpApi.ts

@@ -49,6 +49,18 @@ export function buildSavePayload(input: BuildSavePayloadInput) {
 
   const isPageActive = !isEditingHeader && !isEditingFooter;
 
+  // I-1 (data-loss): `activePageId` can go dangling -- e.g. the original
+  // Home page (id 'home') is deleted, its replacement gets a fresh id
+  // (`page_<ts>`), and a reload re-initializes `activePageId` back to the
+  // hardcoded default `'home'` (see PageContext's `useState('home')`) before
+  // `load()` has a chance to point it at the actually-restored page. If a
+  // real page IS active but matches no entry in `pages`, treat `pages[0]`
+  // (the landing page) as the active one so the live canvas serialization
+  // still reaches the index.html page slot / `pages_craft_state[0]` instead
+  // of only the legacy top-level `craft_state`/`html` fields.
+  const activePageIndex = isPageActive ? pages.findIndex((p) => p.id === activePageId) : -1;
+  const effectiveActivePageId = activePageIndex !== -1 ? activePageId : pages[0]?.id;
+
   // Fresh header/footer state: the live canvas wins when that zone is the
   // one currently being edited; otherwise fall back to the last-committed
   // stored state (updated on zone switch by PageContext's saveCurrentState).
@@ -115,7 +127,7 @@ export function buildSavePayload(input: BuildSavePayloadInput) {
     const filename = i === 0 ? 'index.html' : page.slug + '.html';
     let pageHtml = '';
 
-    if (isPageActive && page.id === activePageId) {
+    if (isPageActive && page.id === effectiveActivePageId) {
       // Active page: use the current canvas HTML (already exported above)
       pageHtml = currentHtml;
     } else if (page.craftState) {
@@ -146,7 +158,7 @@ export function buildSavePayload(input: BuildSavePayloadInput) {
     // reload the editor's clean-URL routing (.htaccess rewrite of /name →
     // name.html) lines up with the file we just wrote (index.html).
     slug: i === 0 ? 'index' : page.slug,
-    craftState: (isPageActive && page.id === activePageId) ? liveCraftState : (page.craftState || null),
+    craftState: (isPageActive && page.id === effectiveActivePageId) ? liveCraftState : (page.craftState || null),
   }));
 
   return {
@@ -177,6 +189,7 @@ export function useWhpApi() {
     setHeaderCraftState,
     setFooterCraftState,
     setPagesCraftState,
+    setActivePageIdDirect,
   } = usePages();
 
   const save = useCallback(async () => {
@@ -271,10 +284,23 @@ export function useWhpApi() {
             console.warn('Failed to load page state:', e);
           }
         }
+
+        // I-1 (data-loss): point activePageId at the page we just loaded
+        // into the canvas. Without this, activePageId stays at whatever it
+        // was initialized to (the hardcoded default 'home'), which goes
+        // dangling the moment the original Home page has been deleted and
+        // replaced (its replacement gets a fresh `page_<ts>` id) -- the next
+        // edit+save would then only reach the legacy top-level fields
+        // instead of the actual page slot. Only do this when a real page is
+        // being loaded, i.e. we're not currently mid-edit of the header/
+        // footer zone (switching zones is handled separately by switchPage).
+        if (!isEditingHeader && !isEditingFooter) {
+          setActivePageIdDirect(firstPage.id);
+        }
       }
     }
     return data;
-  }, [isWHP, whpConfig, actions, setHeaderCraftState, setFooterCraftState, setPagesCraftState]);
+  }, [isWHP, whpConfig, actions, setHeaderCraftState, setFooterCraftState, setPagesCraftState, setActivePageIdDirect, isEditingHeader, isEditingFooter]);
 
   const uploadAsset = useCallback(
     async (file: File) => {