register
Register the handler for a patch slot.
Copy-on-write even when the array already fits: a plain store into the live array gives a reader no happens-before, and only the volatile publish below does. Installs are rare, so copying is cheaper than having to reason about when a fire would see the store.
Parameters
slot
the index minted for this install, inlined into the woven advice as a constant
h
the game-side handler to invoke when that slot fires