If the counter example is changed to run more steps than 270, it behaves in a way that was surprising to me. It resets once, at 256, but after counting back up from 0, it then continues past 256.

That might be what was intended, the comment that it "resets when it reaches 256" is perhaps just unclear. Since this was the second copilot program I tried, my impression was that it wasn't working right somehow.

Here's a version that behaved how I expected it to behave.

bytecounter :: Stream Int32
bytecounter = counter true reset where
reset = let n = counter true false
in n mod 256 == 0

(And I'm very impressed, BTW, that I was able to write the natural haskell code there, and it just worked in the copilot EDSL!)