cadical VS jnisat

That is true, but there are many interesting heuristics in modern SAT solvers, such as kissat: https://github.com/arminbiere/kissat (winner for a few years now). LBD ("glues" in glucose) is one of them. Kissat is actually quite readable. More readable is CaDiCaL, also extremely fast and effective: https://github.com/arminbiere/cadical

I personally also develop a SAT solver called CryptoMiniSat, but the above two are easier to read :)

You'd probably end up with thousands of variables and tens / hundreds of thousands of constraints. You'd assign each variable a number, then feed the whole mess of constraint equations into an off-the-shelf SAT solver like Cadical, then interpret the solver's results in terms of puzzle piece positions.

Alongside with the SAT solver interface and its extensions, `kotlin-satlib` provides wrappers for native SAT solvers (these days, most of them are written in C/C++) implemented using JNI technology. Currently, the solvers included are: MiniSat, Glucose, Cadical and CryptoMiniSat. Sadly, `kotlin-satlib` won't work out-of-the-box, you have to provide it with some external SAT solver, either in the form of a library or a binary. Luckily, there are build instructions for each of the supported SAT solver, both for Linux and Windows. Checkout the README!

The project itself was originally based on https://github.com/mmaroti/jnisat.