[nclack]

Verify every advertised NGFF extent directly from S3 with TensorStore before writer flush or close. CPU and GPU tests share the filesystem fixture, analytic references, metadata checks, and codec table: 30 codec/buffering combinations plus a multipart case per backend.

A test-only aiohttp proxy delays shard completion while the reader checks published extents. Missing/corrupt-shard and premature-metadata probes cover all three levels; explicit read bounds handle concurrent metadata growth. Each run cleans up its own bucket, including failed setup. CTest runs both variants in the existing S3Mock CI jobs.

Validation:

• Native CPU readback checks: 4/4 passed; GPU: 3/3 passed. All 31 S3 cases passed on each backend.
• CPU Docker S3 readback passed.
• Bypassing the publication fence fails on missing shard data; an injected proxy startup failure leaves no bucket.
• C/Python formatting, new Python test lint, and whitespace checks passed.

Closes #34.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
see 3 files with indirect coverage changes

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