code-box/background/messages/sidepanel.ts

import type { PlasmoMessaging } from "@plasmohq/messaging"

const handler: PlasmoMessaging.MessageHandler = (req, res) => {
  chrome.tabs.query({ active: true, currentWindow: true }, ([tab]) => {
    chrome.sidePanel.open({ tabId: tab.id })
  })
}

export default handler