ReadonlyblockThe assembled block, or null when the kind cannot be assembled from deltas.
ReadonlyblockReadonlyclosedTrue when a block-end chunk closed this block.
ReadonlyindexThe index the adapter used to correlate this block's chunks.
ReadonlyordinalFirst-seen position, 0-based and contiguous.
This — not index — is what a durable assistant/block row should use as
its blockIndex, because adapter indexes are only required to be distinct,
not dense, while the signed sequence must be both.
ReadonlyoutcomeReadonlypartialRaw accumulations; non-null exactly when block is null.
One block of a stream, with its outcome. Every opened index produces one.