* s3: return the multipart object checksum in the CompleteMultipartUpload body
S3 carries the flexible-checksum members of CompleteMultipartUploadResult in
the XML body, not in response headers, so every SDK read back an empty
checksum from an upload that asked for one.
Claude-Session: https://claude.ai/code/session_01Huux1uh7JxAbf8yypMYrMk
* s3: echo the checksum algorithm and type from CreateMultipartUpload
The upload directory already records both, but the response dropped them, so a
client could not confirm which checksum its parts had to carry.
Claude-Session: https://claude.ai/code/session_01Huux1uh7JxAbf8yypMYrMk
* test: multipart upload reports the object checksum it was asked for
Covers every algorithm end to end: the create response echoes the algorithm and
type, the complete response carries the checksum, and it matches what a later
HEAD reports.
Claude-Session: https://claude.ai/code/session_01Huux1uh7JxAbf8yypMYrMk
CRC64NVME multipart objects now emit a full-object checksum instead of a composite base64-N value, matching AWS (CRC64NVME supports full-object only). Adds x-amz-checksum-type handling (COMPOSITE/FULL_OBJECT) for CRC32/CRC32C/CRC64NVME via CRC combination, resolved at CreateMultipartUpload and applied at completion.
Chris Lu