I am currently implementing S3, with correct error handling for edge cases. Its been about a month and I have almost the whole API surface done, with some gaps (you actually need a broader surface eg some IAM, KMS encrytion needs a persistence layer so only done sse-c so far). Close to the point where you could drop it in as a local emulation tool, its a sub 9MB binary (Rust).

Literally as I write this the AI code review said "suspended-bucket current-version selection is still wrong when the numbered version and the newer null version land in the same millisecond." - thats the level of detail you have to deal with.