The behaviour a node's compute module implements — the recompute for ONE op, the per-cell unit of work.

A ReactiveDag.Node records its compute module in cell.meta.compute; the generic ReactiveDag.Node.Recompute strategy dispatches to it. The op reads its inputs (the input cells' rows, and/or the host's own resources) and writes its output, returning the keys that ACTUALLY changed — only those propagate, keeping the cascade O(real changes).

This is deliberately thin: the substrate says WHEN a cell recomputes and in what order; the op says HOW, in whatever storage/effect model the host uses (per-key Elixir calling an LLM, or a set-based SQL write). The library never inspects what an op does — only that it returns {:ok, changed_keys}.

A LEAF has no op: an external source writes its rows and marks its parents dirty, so a leaf never reaches recompute.

There is no coordination write

This module used to carry put/3, delete/2 and tombstone/2, routing to a configured CoordinationWriter that wrote a row per (cell_id, key) into a side table. Every node now writes its results into its own resource, so that table had nothing left to record that the resource does not already say — and an op's return value is the changed set, which is what the drain actually propagates. An op writes its rows and returns its keys; nothing else is asked of it.