piece

Merge two replicas' op-logs. The result is idempotent set-union — both replicas converge to the same toList after piece.

Satisfies the Quilted lattice laws:

• Idempotent: a.piece(a) converges to a

• Commutative: a.piece(b) == b.piece(a)

• Associative: a.piece(b).piece(c) == a.piece(b.piece(c))

Any FugueOp.Compact ops in the union are applied eagerly so that Insert/Remove ops already GC'd on one peer do not re-inflate the op-log on merge.