I worked a little bit more on it, and thanks to my refactoring I have identified a bug in the original code (which I have intentionally retained in my own code because the point is to produce the same output as the original version, all the way down to and including bug-for-bug compatibility).
Description of bug, which I also posted as a comment on the OP gist:
> Player and other entities will never be placed on the rightmost column of the room floor, nor on the bottom-most row of the room floor. See https://gist.github.com/ctsrc/fef3006e1d728bb7271cff0656eb02... [...]. In my refactored version of your code the bug is explained at the line I linked to in this comment.
Description of bug, which I also posted as a comment on the OP gist:
> Player and other entities will never be placed on the rightmost column of the room floor, nor on the bottom-most row of the room floor. See https://gist.github.com/ctsrc/fef3006e1d728bb7271cff0656eb02... [...]. In my refactored version of your code the bug is explained at the line I linked to in this comment.
https://gist.github.com/munificent/b1bcd969063da3e6c298be070...