Two separate Relates strongly holding each other's key as their value
(inst->slot in one, slot->inst in the other) is a mutual-reachability
cycle that ordinary weak-key GC can't resolve on its own -- the case
Lua 5.2 ephemerons exist for. Weaken both to pure lookups and make
bindLifetime/unbindLifetime (already used for Slot's own observers)
the single GC anchor for the slot object itself, which attachSlot/
destroySlotTree were missing.
Audited every other Relate() in base/ for the same shape (an object
other than inst used as the outer key) -- slotOwner was the only one;
everything else either has no back-reference to inst or is the safe
single-table self-reference shape bindLifetime already relies on.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
