How should we enforce that only a single board object exist for onboard implementations?

[metasoarous]

One way would be to memoize the get-board function such that it always returns the same object. This could work somewhat similarly for overwire boards, except that the instantiation memoization would also look at :port, or whatever can be used as a unique identifier as to which board is behind the scenes. However, for overwire, it may be possible to write things such that this isn't necessary, if it always looks up state things directly from the board instead of caching :mode values and such.