fix(editor): prevent focus loss when typing in header/footer editors (SD-1993)

Replace unconditional appendChild calls in DomPainter.updateVirtualWindow()
with cursor-based DOM reconciliation that skips moves for elements already
in the correct position. Add focus save/restore safety net in
PresentationEditor.#flushRerenderQueue for edge cases.

Author: tupizz

packages/layout-engine/painters/dom/src/renderer.ts

@@ -1709,8 +1709,13 @@ export class DomPainter {
     }
     this.mount.appendChild(this.bottomSpacerEl);
 
-    // Ensure mounted pages are ordered (with gap spacers) before bottom spacer.
+    // Ensure mounted pages are ordered (with gap spacers).
+    // Use cursor-based reconciliation to skip DOM moves for elements already in
+    // the correct position. Moving an element via appendChild/insertBefore triggers
+    // a browser blur event on any focused descendant, which breaks header/footer
+    // in-place editing where a PM editor lives inside a page element (SD-1993).
     let prevIndex: number | null = null;
+    let cursor: ChildNode | null = this.virtualPagesEl.firstChild;
     for (const idx of mounted) {
       if (prevIndex != null && idx > prevIndex + 1) {
         const gap = this.doc!.createElement('div');
@@ -1721,10 +1726,16 @@ export class DomPainter {
           this.topOfIndex(idx) - this.topOfIndex(prevIndex) - this.virtualHeights[prevIndex] - this.virtualGap * 2;
         gap.style.height = `${Math.max(0, Math.floor(gapHeight))}px`;
         this.virtualGapSpacers.push(gap);
-        this.virtualPagesEl.appendChild(gap);
+        this.virtualPagesEl.insertBefore(gap, cursor);
       }
       const state = this.pageIndexToState.get(idx)!;
-      this.virtualPagesEl.appendChild(state.element);
+      if (state.element === cursor) {
+        // Already in the correct position. Skip the DOM mutation.
+        cursor = state.element.nextSibling;
+      } else {
+        // Out of order. Move to the correct position.
+        this.virtualPagesEl.insertBefore(state.element, cursor);
+      }
       prevIndex = idx;
     }
 

packages/super-editor/src/core/presentation-editor/PresentationEditor.ts

@@ -3165,13 +3165,34 @@ export class PresentationEditor extends EventEmitter {
     }
     this.#pendingDocChange = false;
     this.#isRerendering = true;
+
+    // Capture H/F editor focus state before rerender so we can restore it if
+    // a DOM mutation (e.g. page re-ordering in updateVirtualWindow) causes the
+    // browser to blur the active header/footer editor (SD-1993).
+    const sessionMode = this.#headerFooterSession?.session?.mode ?? 'body';
+    const activeHfEditor = sessionMode !== 'body' ? this.#headerFooterSession?.activeEditor : null;
+    const hadHfFocus = activeHfEditor?.view?.hasFocus?.() ?? false;
+
     try {
       await this.#rerender();
     } finally {
       this.#isRerendering = false;
       if (this.#pendingDocChange) {
         this.#scheduleRerender();
       }
+
+      // Restore focus if the H/F editor lost it during rerender.
+      if (hadHfFocus && activeHfEditor?.view) {
+        const doc = this.#visibleHost.ownerDocument;
+        const editorDom = activeHfEditor.view.dom;
+        if (doc && !editorDom.contains(doc.activeElement)) {
+          try {
+            activeHfEditor.view.focus();
+          } catch {
+            // Ignore focus errors during recovery
+          }
+        }
+      }
     }
   }