[justapithecus]

Summary

A Quarry run against R2 stalled for ninety minutes on one write and then failed with path already exists. The SDK had retried a PutObject whose response the network lost, and the retry met the object the first attempt had stored. The S3 adapter read the refusal as another writer's object, so a Put that had succeeded returned ErrPathExists, and the commit on top of it failed. The adapter now recognises its own upload.

Highlights

• The contract states the exception. CONTRACT_STORAGE.md § Put: where the backend reports a content digest the adapter can compare with its payload's, a refused conditional create is a success when the stored object's length and digest equal the payload's. When either differs, or the comparison fails, Put returns ErrPathExists as before.
• The S3 adapter compares length and ETag. Put hashes the payload as it spools it. On a precondition failure the atomic path reads the object's HEAD and returns nil when its length and ETag equal the payload's length and MD5, which an S3 store gives a single-part object. A multipart ETag carries a part count and never matches. A HEAD that fails leaves the refusal in place.
• The mock gives S3's ETag. The test client's ETag was a SHA-256. It is now the quoted MD5 that S3 gives, and HeadObject reports length and ETag as S3 does.
• Tests. A client that stores the object and then refuses, as a backend does after a lost response, makes Put succeed with the bytes in place. Another writer's object, a HEAD that fails, and a multipart ETag each keep ErrPathExists. The existing duplicate-write test writes other bytes for the refusal and the same bytes for the success.

Test Plan

• task lint and task test pass, with the four new cases and the adjusted duplicate-write case.
• The prose gate on the contract text, the changelog entry, the new comments and this body.
• Codex round 1: no findings.
• Bot review of fd46186a: no findings.
• Bosun's changelog check failed on the first head, since the entry ran to 103 words against the limit of 90. Commit d142e63d shortens it to 81.

🤖 Generated with Claude Code

[chatgpt-codex-connector]

Codex Review Summary: ✅ Completed

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-08T15:25:32.705339Z	fd46186	PR opened

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