Pin the engine of the world editor the user has open, so engine tools (execute, capture, …) drive it for the rest of this conversation. An engine that is already connected returns at once. It is held only for an engine that is about to connect: once the editor has drawn its first frame the call holds, up to about 30 s, until the engine connects. In every other case it answers at once with `connected: false` and what the editor is doing (`editor.state`: never_opened, launching, booting, connecting, stalled, failed, started_not_connected), so while an editor is still loading do what needs no engine and call this again when you need one. `waited_ms` is how long the call was held (0 when it was not) and `wait` says how the wait ended. It opens nothing: nothing on the server can open a browser. Call world.open first and act on its `next`, which says whether you show the user a link or run a command on their machine. A world with engines on more than one branch is refused rather than guessed at: name the `branch`, or use session.list / session.connect to pick one engine outright.