A core StorageAdapter. Consume/cancel get streams; retain ownership of the S3 client.
Remarks
Replacement never deletes the old key first. Failures settle active work before abort;
cleanup failures are preserved. A lost completion response yields COMMIT_OUTCOME_UNKNOWN,
requiring reconciliation rather than claiming rollback. Empty multipart support is backend-specific.
Create strict multipart storage with bounded upload concurrency and byte-preserving reads.