Accumulation mode

Accumulation mode - what a refired window does about its previous output: the accumulating vs discarding mode choice decides whether the new result replaces the last one or only carries what arrived since. In accumulating mode each firing emits the full running value: pane two says 12, meaning 12. In discarding mode each firing emits only the delta: pane two says 5, meaning 5 more.

The trap is that the two are indistinguishable on the wire, both just rows with numbers in them. Pair an accumulating producer with a consumer that sums panes and every refire double-counts; pair a discarding producer with a consumer that overwrites and the totals quietly come up short. The setting hides inside trigger configuration, and it quietly decides whether your totals are right.

Do you need it? Only if you switched on early and late firings, which is how the leopard gets you: one buried knob deciding whether the revenue numbers are right. Ubik never asks the question. A window fires once, and a continuous view republishes the full running value per key as an upsert, so replace-by-key is the contract rather than a mode.