Nice :) I referenced the below but ended up making my own impl that keeps data structures serialisable (just arrays and gl-matrix) and avoids allocations.

github.com/FedUni/caliko
github.com/lo-th/fullik
editor.p5js.org/rjgilmour/sk...

also enjoyed (for 2d fabrik):
www.youtube.com/watch?v=NfuO...

Per usual, the sketch is open source and can be found on my website / github:

live: sketches.isaacmason.com/sketch/crawler
github: github.com/isaac-mason/...

This is my first stab at foot placement procedural animation so my approach is fairly rudimentary.
tl;dr

- raycast to find an ideal foot position
- step if the current vs ideal distance exceeds some threshold, and a leg is within their slot in a repeating step phase timer

I created a handful of controls to quickly throw together new "crawlers". If I use this in a game someday I'd imagine creating a bunch of different characters and enemies just with different crawler configurations.