Zero-based position of this batch in the chunked sequence.
Whether sending was attempted. See BatchUpsertDisposition.
The documents this batch carried, ready to be passed back in for a retry.
What the attempt produced, or a Errors.PineconeBatchUpsertUnsentError for an unsent batch.
error.message, lifted out so a failure can be logged or serialized without unwrapping.
One failed batch within a batched upsert.