Where to open Chrome's DevTools on the page this session is evaluating in — the same realm, the same DOM, the same paused frame. null where this browser has none to serve them from.

The point is that it is the SAME page rather than another one at the same address: a value declared at the prompt is in the console there, and a debugger shows as paused in both. The frontend is Chrome's own, served over localhost — no network, no extension.

It needs an HTTP debugging endpoint, which is what the Chrome this process pre-launched has. A session that fell back to a browser Playwright launched talks over a pipe and gets null — today that is macOS, where nothing is pre-launched, and any headed session, which has F12.