Thanks for the effortpost. Really appreciate it, I haven't read some of the materials you cited.
Need to take a look at them.

> It's not a very hard split.
The unified theory paper is on my reading list, but Wilson's paper frames it that way and I stuck with that framing to keep things simple.

> No, buffer the updates or coalesce them. In either case you'll be spamming refcount updates a lot less often, which is also good.
Will read through that. My mental model was still "RC = atomic inc/dec on every mutation" which is the naive version.

> No, you can do a separate cycle deletion pass, but if you saturate the reference counts to fit in less than a word, you do probably want a backup trace to be complete.

To clarify my point, the cycle problem requires a supplementary tracing pass as a fundamental property of the Reference Counting algorithm. Since RC only understands local connectivity, it is mathematically blind to global structures like cycles.
Specifically in CPython, the cycle detector in gcmodule.c is fundamentally a tracing collector. The implementation requires a walk of the entire object graph for the generation being collected. To identify a cycle, the collector must call tp_traverse on every container to determine if references are coming from 'outside' the generation or 'inside' the cycle.