The provider contract (metadata addToIndex/removeFromIndex, vector
addItem/removeItem, id-mapper getOrAssign/remove) gains an optional
trailing generation — evaluated lazily at operation execute time (the
graph surface's thunk pattern, generalized), threaded from all 17
construction sites: undefined during generation-0 bootstrap, the real
committed generation everywhere else. Optional = additive: no existing
provider or caller breaks; native delta logs that stamped literal zero
start hearing truth. JS twins accept the parameter with parity notes.
Pins: provider doubles capture and assert nonzero monotonic generations
across add/update/remove on both surfaces.
