ui-eng-vision-widget-promoter

Development

Promotes legacy views to modern UI.Widget classes, hooks up performUpdate() rendering, and exports default views.

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Subskill: Widget Promoter (Pass 3)

This subskill completes the architectural transition, upgrading the component from legacy base classes (like SimpleView or custom wrapper layouts) into clean UI.Widget classes that use native update rendering delegates.

1. Widget Promotion Guidelines

Change Class Inheritance:
- Rewrite class declarations to extend UI.Widget (or specialized sub-layouts like UI.Widget.VBox).
- Clean up and remove older constructors that perform custom container initializations or access .element directly for manual append operations.

Upgrade View Delegates & Inject View:

Migrate the local Lit template strings into a formally exported default view layout:

export const DEFAULT_VIEW: View = (input, output, target) => {
  Lit.render(html`...`, target);
};

Make the view injectable in the constructor for testability (as per docs/ui_engineering.md):

class MyWidget extends UI.Widget.VBox {
  #view: View;
  constructor(element?: HTMLElement, view: View = DEFAULT_VIEW) {
    super(true, element);
    this.#view = view;
  }

Implement the standard modern performUpdate() override on the widget:

override performUpdate(): void {
  this.#view(this.viewInput, this.viewOutput, this.contentElement);
}

Clean Up Legacy Wrappers:
- Remove any LegacyWrapper bindings or custom wrappable custom elements.
- Replace old panel instantiations with standard <devtools-widget> declarative entries:
```
html`<devtools-widget .widgetConfig=${widgetConfig(MyWidgetClass, [params])}></devtools-widget>`
```
- Inspect instantiator files (e.g., ApplicationPanelSidebar.ts) and decouple any direct accesses to .element.

2. Safety & Verification Rules

CRITICAL: Never update screenshot goldens without explicit consent of the user. Most likely the failure points to an issue in the implementation or (less likely) the test itself. Look at the screenshot diffs to debug.
Minimal Code Movement: When migrating, try to move code around as little as possible, in particular around the lit rendering helpers. This minimizes the git diff and improves reviewability.