/prepare-regression

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.