It's harder than you'd expect. Depending on what kind of bucketing an arena does (by size or by type), a stale reference may end up pointing to another piece of memory of the correct type, which is still wrong, but more subtly than a crash.

Look at the architecture of lightpanda and come back with a response.

I'm not familiar enough with Zig to want to dive into architecture, the point I wanted to make is general to arenas in any language that can have a stale reference.

I once had a stale stack reference bug in C that lived for a year, because the exact same object was created at the exact same offset every time it was used, which is a similar situation.