reset

Reset the counter to zero: clear the store and carry the current causal context forward. Returns the delta to absorb with piece; the receiver is unchanged.

Any increment concurrent with this reset — minted on a replica that had not yet seen the reset — will survive the merge, because its dot is not in this reset's context.

O(1). The Causal invariant guarantees every live dot is already in causal.context (see class KDoc), so no fold over live dots is needed — the context is already complete.