---
title: "2026-08-07 Histo S3 I/O migration semantics review"
description: "Adversarial review found unsafe resume mixing, incorrect virtual TIFF resolution, shard-dependent inference, and calibration drift."
image: "https://docs.virdx.dev/img/virdx-social-card.png"
---

> Documentation Index
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# 2026-08-07 Histo S3 I/O migration semantics review

## Work Done

Read both `main` and `feat/fk/s3-io` versions of the `src/histo` migration, focusing on the new `histo.io` seam, physical resolution/rounding, resume semantics, and weakened errors. Ran small pixi-based checks that demonstrated: a partial writer resumes across a changed physical geometry; TIFF `Level.mpp(1.5)` reports a shape and MPP inconsistent with the returned array; non-square pyramid rounding stamps the x axis with the y downsample; and OME-XML-only calibration is discarded by the TIFF adapter. Also identified removal of panoptic input fingerprints and shard-dependent gland inference windows. Reported exact priorities and source locations to the parent review agent. No histo repository files were edited.

## Lessons Learned: Pitfalls

The general histo workstream overview did not contain I/O seam or migration invariants and was not directly useful for this narrow diff review. The branch's tests emphasize surface parity and happy-path stored levels but omit adversarial resolution requests, changed-job resume, axis-specific rounded pyramid dimensions, and calibration sources other than TIFF resolution tags.

## Lessons Learned: Improvements

Document and test a migration contract for resumable artifacts: persisted geometry, layout, inputs, model/config fingerprints, and code version must match before any shard is reused. Add property tests asserting `image.read(region).shape` agrees with the pinned geometry for arbitrary requested MPPs, and that every pyramid level preserves per-axis physical extent within rounding tolerance. Maintain a format calibration matrix (TIFF tags, OME-XML, SVS, NDPI, NGFF units) at the I/O seam.

Source: https://docs.virdx.dev/knowledge/inbox/2026-08-07-histo-s3-io-migration-semantics-review/index.mdx