Where the PAGE is served, e.g. http://localhost:1234 — the application, as a browser sees it.

Worth holding apart from ReplSession.inspector, which is the other address a session has. Opening this one in a browser gets a FRESH DOCUMENT: same server, same routes, but a second realm that shares no bindings, no DOM and no module state with the prompt. Opening inspector gets a second VIEW of the realm the prompt is already typing into.