prepare-regression

Name: prepare-regression
Author: trailofbits/skills

$npx mdskill add trailofbits/skills/prepare-regression

Input: PR URL or repository plus commit/range, and registry assignment. Follow [project guidance](../../references/evidence.md#project-guidance) after resolving the target commit.

SKILL.md

.github/skills/prepare-regressionView on GitHub ↗

---
name: prepare-regression
description: Use when pinning before/after sources and collecting PR or commit context for a regression investigation.
---

# Prepare a change

## When to Use

Input: PR URL or repository plus commit/range, and registry assignment.
Follow [project guidance](../../references/evidence.md#project-guidance) after resolving the target commit.

## When NOT to Use

The same inputs have a verified preparation record; reuse it.

## Prepare

1. Read the [standard](../../docs/regression-definition.md) and
[file contract](../../references/evidence.md). Pin the complete change as S0/S1:
commit parent or explicit range baseline; merge base to frozen head for unmerged
PRs; merge first parent to merge commit, squash parent to squash, or the complete
rebased series for merged PRs. Ambiguous ranges and missing root baselines block
preparation.
2. Freeze commit titles/messages or PR title, body, discussion, reviews and inline
comments with URLs and collection time. Paginate APIs; record limits and
lifecycle. Locate security/threat-model documents in both states; record paths
or search limitations.
3. Run [snapshot.py](../../scripts/snapshot.py) via `uv run --no-project` with
repository, S0, S1 and a new directory, or equivalent Git commands for special
source needs. Preserve dependency/submodule/LFS revisions. Exclude later history;
keep exports pristine and build in separate copies.
4. Write and seal `prepare.json` with boundary explanations, frozen context and
source artifacts. If blocked, preserve collected evidence and name the prerequisite.

## Report Back

Keep detailed evidence in the sealed package. Return only:

- Status: `complete` or `blocked`, matching the record.
- Record: sealed `prepare.json` path, or why none was produced.
- Result: selected S0/S1 and material collection limitations.
- Blocker: missing prerequisite or required caller action, if blocked.

## Rationalizations to Reject

- “The PR is merged”: that does not identify the complete change boundary.

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