src/vs/workbench/contrib/notebook/browser/notebookRendererMessagingServiceImpl.ts/NotebookRendererMessagingService/postMessage
class NotebookRendererMessagingService:	private postMessage(editorId: string, rendererId: string, message: unknown): void {
		if (!this.activations.has(rendererId)) {
			this.prepare(rendererId);
		}

		const activation = this.activations.get(rendererId);
		const toSend = { rendererId, editorId, message };
		if (activation === undefined) {
			this.postMessageEmitter.fire(toSend);
		} else {
			activation.push(toSend);
		}
	}