src/vs/workbench/browser/parts/panel/panelPart.ts/BasePanelPart/onDidRegisterExtensions
class BasePanelPart:	private onDidRegisterExtensions(): void {
		this.extensionsRegistered = true;

		// hide/remove composites
		const panels = this.getPaneComposites();
		for (const { id } of this.getCachedPanels()) {
			if (panels.every(panel => panel.id !== id)) {
				if (this.viewDescriptorService.isViewContainerRemovedPermanently(id)) {
					this.removeComposite(id);
				} else {
					this.hideComposite(id);
				}
			}
		}

		this.saveCachedPanels();
	}