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.

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1. Widget Promotion Guidelines

• Widget Framework Rules: Follow the rules defined in devtools-ui-widgets.

1. 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.
   • Note that VBox and HBox inherit directly from Widget. They fully support view injection (view = DEFAULT_VIEW), performUpdate(), and requestUpdate() without modification.

2. 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), and use static INJECT if requesting dependencies from Universe:

     class MyWidget extends UI.Widget.VBox {
       static override readonly INJECT = [SDK.TargetManager.TargetManager] as const;
     
       #targetManager: SDK.TargetManager.TargetManager;
       #view: View;
       constructor(
         element?: HTMLElement,
         [targetManager]: UI.Widget.WidgetDependencies<typeof MyWidget> = [],
         view: View = DEFAULT_VIEW,
       ) {
         super(element);
         this.#targetManager = targetManager;
         this.#view = view;
       }

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

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

3. 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.

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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.

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🔍 Mental Audit (Internal Self-Correction)

Before reporting back or committing, re-read the instructions and verify:

1. ❓ Decoupling: Did I remove all direct .element or .contentElement couplings from instantiator files?
2. ❓ Inheritance: Does the class now cleanly inherit from UI.Widget or its variants?
3. ❓ Injectability: Is the view injectable in the constructor?
4. ❓ Build: Does the code compile and do tests pass?