# Flag Hidden Binary Files in Tests

Flag Hidden Binary Files in Tests: what it does, its label on each agent, what it misses, and examples.

Catalog policy opaque-blob-guard, version 0.0.5, labelled warns on Claude Code.

> Ask the user before running any command on this page: each one changes how their agent or repository behaves.

## What it does

Warns (observe rollout; never refuses yet) when a change adds or edits, in tests/, fixtures/, testdata/, spec/, m4/, vendor/, gradle/wrapper/: a file whose first bytes are an archive, executable, wasm or database signature (any extension), a random-looking non-media file over 100 KB, or a symlink out of the repo; m4/configure/Makefile text that decodes and evaluates; a gradle wrapper jar changed with no new distributionSha256Sum. Misses text-encoded or prefixed payloads, other folders.

## On each agent

| Agent | Label | What it does there |
| --- | --- | --- |
| Claude Code | Warns | Warns on an agent's file writes and at turn end |
| Cursor | Warns | Warns on an agent's file writes and at turn end |
| Codex | Warns | Warns on an agent's file writes and at turn end. If the hook errors, the action goes through (not witnessed; the vendor's row is only partly live-run) |
| GitHub Copilot | Warns | Warns at turn end only. It does not check a file write when it happens. If the hook errors, the action goes through (not witnessed; the vendor's row is only partly live-run) |
| Devin | Warns | Warns at turn end only. It does not check a file write when it happens. If the hook errors, the action goes through (vendor docs only, not witnessed) |
| Grok | Not graded | Not graded yet for Grok |
| goose | Not graded | Not graded yet for goose |
| Antigravity | Not graded | Not graded yet for Antigravity |
| OpenHands | Not graded | Not graded yet for OpenHands |
| Kimi Code | Not graded | Not graded yet for Kimi Code |
| Factory Droid | Not graded | Not graded yet for Factory Droid |

## What it misses

This policy does not state what it misses.

## Examples from its eval suite

Warns: A commit adds an archive under testdata/ with a .txt name (roadmap xz-in-testdata, the signature is what counts).

Allowed: A person commits a binary fixture together with an allowlist entry holding its path and sha256.

## More

- [The policy on the catalog pages](https://chock.sh/coding/policies/opaque-blob-guard/)
- [Source at the pinned catalog commit](https://github.com/open-coder-ai/chock-catalog/tree/1e60d211c1bb767152c6ab0167932da06ab3a10f/base/opaque-blob-guard)


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