sitesmith: pre-create section-inner/bg-section-inner/form-inner linkedNodes

The Invariant 'component type (undefined) does not exist in the resolver'
was Craft.js's toNodeTree choking on the linkedNode that <Element id="X">
auto-creates at render time inside Section / BackgroundSection /
FormContainer. The auto-created node stores its type as the Container
React component class itself, not as {resolvedName:'Container'}, so the
later type.resolvedName lookup returns undefined.

For each shell, treeToState (and apply-ai-response's buildNodeTree) now
synthesizes the linkedNode container up-front with a proper serialized
type, moves the AI's direct children into it, and reparents them. This
matches the canonical shape Craft.js writes when the user manually builds
a site, so Craft.js never has to materialize the linkedNode itself.

craft/src/state/PageContext.tsx

@@ -12,6 +12,18 @@ import { useSiteDesign, SiteDesign } from './SiteDesignContext';
  * because the shell claims to be a canvas but its render ignores `nodes`. */
 const CANVAS_TYPES = new Set<string>(['Container']);
 
+/** Shells that wrap their content in a single <Element id="<key>" is={Container}>.
+ * When the AI puts content directly under one of these, the children end up
+ * orphaned (the shell ignores data.nodes — it renders via the linkedNode) and
+ * Craft.js auto-creates the linkedNode at render time with a botched type
+ * field, which then crashes toNodeTree. Pre-create the linkedNode ourselves
+ * to keep the state shape Craft.js expects. */
+const SHELL_INNER: Record<string, string> = {
+  Section: 'section-inner',
+  BackgroundSection: 'bg-section-inner',
+  FormContainer: 'form-inner',
+};
+
 interface PageContextValue {
   pages: PageData[];
   headerPage: PageData;
@@ -340,9 +352,56 @@ export const PageProvider: React.FC<{ children: ReactNode }> = ({ children }) =>
         if (!cur.columns || cur.columns !== childIds.length) cur.columns = childIds.length;
         (nodes[id] as any).props = cur;
       }
+      // Section/BackgroundSection/FormContainer each render a single
+      // <Element id="<key>" is={Container} canvas> ... </Element>. If the AI
+      // nests content as direct children, Craft.js will auto-create the
+      // linkedNode on first render — and store its type as the Container
+      // component class rather than {resolvedName:'Container'}, which then
+      // crashes toNodeTree with "type (undefined) does not exist in resolver".
+      // Pre-create the linkedNode ourselves with the correct serialized type
+      // so Craft.js never has to materialize it.
+      const innerKey = SHELL_INNER[typeName ?? ''];
+      if (innerKey && childIds.length > 0) {
+        const innerId = `${id}__${innerKey}`;
+        nodes[innerId] = {
+          type: { resolvedName: 'Container' },
+          isCanvas: true,
+          props: { tag: 'div' },
+          displayName: 'Container',
+          custom: {},
+          hidden: false,
+          parent: id,
+          nodes: [...childIds],
+          linkedNodes: {},
+        };
+        for (const cid of childIds) {
+          if (nodes[cid]) (nodes[cid] as any).parent = innerId;
+        }
+        (nodes[id] as any).nodes = [];
+        (nodes[id] as any).linkedNodes = { [innerKey]: innerId };
+      }
       return id;
     };
     const rootId = walk(tree, null);
+    // DIAGNOSTIC: dump the produced state + scan for type=undefined nodes
+    // so when the resolver invariant fires we can see which node is bad.
+    try {
+      const w = window as any;
+      w.__sitesmithLastTree = tree;
+      w.__sitesmithLastState = nodes;
+      const bad: Array<{id:string; node:any}> = [];
+      for (const [nid, n] of Object.entries(nodes)) {
+        const t = (n as any).type;
+        const name = t && typeof t === 'object' ? t.resolvedName : t;
+        if (!name) bad.push({ id: nid, node: n });
+      }
+      if (bad.length > 0) {
+        // eslint-disable-next-line no-console
+        console.warn('[SITESMITH] nodes with undefined type:', bad);
+      }
+      // eslint-disable-next-line no-console
+      console.log('[SITESMITH] treeToState produced', Object.keys(nodes).length, 'nodes; rootId=', rootId);
+    } catch (_e) { /* diagnostic only */ }
     // Craft.js deserialize requires the root node keyed as 'ROOT'
     if (rootId !== 'ROOT') {
       nodes['ROOT'] = nodes[rootId];