Out of curiosity, do you have any documentation on reifying and reflecting continuations in pure concatenative languages? I did some preliminary work in this direction a bit ago, but found that the pure concatenative languages, like Joy, don't actually have continuations (delimited or undelimited) with the flexibility that I'd like, and Factor's continuations aren't pure. Factor cheats in order to get its stack effects to line up, with a separate continuation stack.

Additionally, if you've managed to crack this puzzle, I'd love to see some documentation accompanying FJS, because it is a major omission from the concatenative literature and nobody seems to actually have anything to read besides the shift/reset white papers.