Hold back an inspector rebuild while a field in it has focus

A rebuild destroys the widget being typed in, and a typed value can change the
very structure that decides whether a rebuild is needed -- a field that says
how many ports a node has. That made such a field unusable: every keystroke
previewed, the preview emitted 'project', refreshValues() saw the signature
change and threw the row away. Dragging the value worked only because a drag
keeps receiving globalpointermove on the destroyed widget.

So refreshValues() now postpones a due rebuild while the focus sits inside the
inspector, and runs it as soon as the field is left. Values are safe in the
meantime: TextField.setValue ignores an edit in progress.

Two handles for that in the toolkit. FocusManager.isWithin(node) also replaces
the parent chain refreshLive() walked by hand, and changeHandlers lets a panel
notice that the focus has gone -- there was no signal for that before.

Nothing in the editor can trigger this today, since the Sequence setting that
did is gone. It is the ground for the List tab, where a row that adds or
deletes an item changes the structure while you type. The e2e check therefore
builds the case out of real parts: type into a field, set the object's parent
from outside -- the parent is part of the structure signature -- and confirm
the input survives and the rebuild follows on Escape.

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

src/ui/FocusManager.ts

@@ -9,6 +9,8 @@ import { collectFocusables, type Widget } from './Widget';
 export class FocusManager {
   /** Global handlers for keys nobody consumed (Delete, Ctrl+Z, …). */
   readonly globalHandlers: ((event: KeyboardEvent) => boolean)[] = [];
+  /** Called after focus moved, so a panel can catch up on work it postponed while being typed in. */
+  readonly changeHandlers: (() => void)[] = [];
   private focusedWidget: Widget | null = null;
   private readonly onKeyDown = (event: KeyboardEvent) => this.handleKeyDown(event);
 
@@ -26,6 +28,15 @@ export class FocusManager {
     this.focusedWidget = widget;
     previous?.onBlur();
     widget?.onFocus();
+    for (const handler of this.changeHandlers) handler();
+  }
+
+  /** Whether the focused widget is `node` or sits inside it. */
+  isWithin(node: Container): boolean {
+    for (let current: Container | null = this.focusedWidget; current; current = current.parent) {
+      if (current === node) return true;
+    }
+    return false;
   }
 
   blur(): void {