src/vs/workbench/contrib/notebook/browser/view/renderers/backLayerWebView.ts/BackLayerWebView/initializeMarkup
class BackLayerWebView:	async initializeMarkup(cells: readonly IMarkupCellInitialization[]) {
		if (this._disposed) {
			return;
		}

		// TODO: use proper handler
		const p = new Promise<void>(resolve => {
			this.webview?.onMessage(e => {
				if (e.message.type === 'initializedMarkup') {
					resolve();
				}
			});
		});

		for (const cell of cells) {
			this.markupPreviewMapping.set(cell.cellId, { ...cell, visible: false });
		}

		this._sendMessageToWebview({
			type: 'initializeMarkup',
			cells,
		});

		await p;
	}