Aha I've been semi-vibe-coding a scheme for esp32c3 and linux at the same time, and forgoing the libc too, so baremetal c. I went with a slightly awkward approach for allocation, with heap being seen as pages, and within pages, fixed size objects of size 8, 16 or 32 bytes. A pair is two words, and either bitpacked or pointer to another object. I'm not far in, vaguely following the Peter Michaux approach.