knack is the second wing of fable — after puzz, which does static logic puzzles. The recipe is the same one running across this repo (mappa's worlds, the Ludographer's board games): generate a vast space from a seed, put an interestingness engine on top. But here we loosen the form: instead of one rigid puzzle shape, a single engine takes discrete moves over a grid and resolves them under a composable library of mechanics. Toggle which mechanics are live and the same engine becomes a different game.
Looser form, but the thing that makes the interestingness engine rigorous survives: every level has a verifiable solution. A breadth-first search over the engine's state graph either reaches a winning state — proving the level solvable and finding its optimal length (par) — or it doesn't, and the level is thrown away at birth. So the solver does the same triple duty as in puzz: it certifies, it grades (difficulty from par + search size + how the route winds), and it curates (ranking seeds by an interest battery). "Watch the engine solve it" replays the exact optimal path the solver found.
Each is a coherent bundle of mechanics with its own win condition. Tangle is the diversity dial: it throws two mechanic families together, and the engine still guarantees a way through. Adding a genre — lasers, gravity, teleporters, patrols — is one bundle module plus the same transition rule; the solver and grader come for free.
Page n yields the identical level on every machine, for ever (seeded xmur3 → mulberry32),
and the search for a good level is seeded too — so /knack/?n=42 is a permalink, and so is its
difficulty and its par.