16 bucket config subresources (versioning, ACL, policy, CORS, lifecycle, etc.) now return honest 501 NotImplemented instead of silently misrouting to ListObjects/GetObject.
CAS keys make verify-on-read free: central verification, x-amz-checksum echo, tombstone GC, and corruption surfacing.
S3 integrity checksums moved from a surface-level adapter into the storage/ingest core via a protocol-agnostic ChecksumProvider seam — every write path verified, replicas re-verify on receive.
x-amz-checksum-CRC32/SHA256 echo on PUT; integrity surfaced to clients so dirty bytes never masquerade as clean. Teaches: client-verifiable integrity, Bolt zero-allocation on read path, Sentinel honesty guarantee.
S3 ListObjectsV2 XML serialization dropped from ~1000 allocations to 16 per op via inlined time formatting and a pre-allocated escape buffer.
Three adaptive feedback loops: gossip fanout scales with cluster size, streaming chunk size adapts to cipher/memory, peer quality feeds quorum decisions.
Threshold-OPRF lets E2EE cas blobs dedup without revealing content hashes — plus adaptive failed-auth backoff and lockout.
Scatter-gather lists across shard owners; leases with correct majority quorum — and the two nasty off-by-one/partition bugs found by audit.
Multipart upload support plus a rigorous 501 strategy for unsupported S3 subresources — honest breadths over silent misbehavior.
The Bolt mindset codified: no heap escapes in hashing/encoding, deadline amortization cuts SetDeadline ~98%, allocation hotspots hunted by profile. Teaches: zero-escape patterns, measurement contracts, trade-off posture.