> Is there an i3 command to (a) leap to another window from a selection and (b) leap back and forth between the window you came from and the window you just chose?

Not for windows as far as I know, but for workspaces, yes: https://i3wm.org/docs/userguide.html#back_and_forth https://i3wm.org/docs/userguide.html#workspace_auto_back_and...