Change Review with Repowise

When a diff is on the table, Repowise turns "what files changed" into "what does this change put at risk" — fusing git history (churn, ownership, co-change) with graph topology (dependents, impact surface), test gaps, security signals, and the architectural decisions that govern the touched code.

Two complementary risk signals, use both:

• get_change_risk(revspec=…) (MCP) scores the whole change as one unit (a commit or a base..head range) from its diff shape: a single 0-10 defect-risk score with drivers (lines added/deleted, files, directories, subsystems, change entropy, author familiarity). No LLM, no network. Prefer this in-MCP tool; it takes a revspec and diffs server-side, so you never shell out. Lead with risk_percentile (this change ranked against sampled recent commits), summarized by review_priority and classification. score is calibrated per single commit, so a PR-sized change reads high by construction, and fallback_band appears only when there was no baseline to rank against. Omit revspec to score uncommitted work. This is the pre-merge gate: "how risky is this change overall?" The repowise risk <revspec> CLI is the identical scorer for when you are already in a terminal.
• get_risk(changed_files=…) (MCP) works per file and returns the directive block, the specific things to check inside the diff.

Score the whole change first

get_change_risk(revspec="main..HEAD")   # HEAD, a commit SHA, or base..head

Read risk_percentile and the top drivers: a high score from large diffusion (many dirs/subsystems) or low author familiarity tells you where to look hardest. extensions=[".py", ".ts"] counts only certain file types; exclude_patterns=["tests/"] omits paths. A warning field means the revspec or filters matched no files, so an all-zero score there is not a clean bill of health. The equivalent from a terminal is repowise risk <revspec> (add --ext .py,.ts or --format json).

Then drill into the directive block

Call get_risk in PR mode by passing the changed files:

get_risk(targets=<changed files>, changed_files=<same changed files>)

The response carries a directive block — read it first, it's a few short lists:

• will_break — files/symbols that depend on what changed but are not in the diff. These are the likely breakages. Check each one.
• missing_cochanges — files that historically change together with the changed files but were left untouched. Often a forgotten update.
• missing_tests — changed code with a test gap. Flag for new/updated tests.
• tests_to_run — the positive complement of missing_tests: the tests the per-test coverage map proves execute the changed files (pytest-runnable ids). Recommend running these to validate the change. Empty until a coverage map is ingested (repowise coverage add); empty is "unknown", never "no tests exist".

pr_blast_radius holds the fuller dossier behind those lists (including the per-changed-file guarding_tests breakdown behind tests_to_run).

For the line-precise version from a terminal, repowise impacted-tests <revspec> maps each changed line to the tests whose recorded coverage touches it, then prints the ids (--format list | xargs pytest runs exactly them). It is honest about gaps: a changed file with no coverage rows is a labelled filename guess, and a brand-new file is "unknown, run the full suite", never "no tests needed".

Then go deeper where it matters

1. Why does this code exist? For any non-trivial changed file, call get_why(query="<file>") — don't let a change silently contradict a recorded architectural decision. Surface conflicts_with / supersedes hits.
2. Did the change make health worse? get_health(targets=<changed files>, include=["biomarkers"]) — call out new complexity, deep nesting, or duplication the diff introduced.
3. Who should review? get_risk ownership + co-change signals suggest the people with the most context on the touched code.

Getting the diff

• A GitHub PR: gh pr diff <number> (or gh pr view <number> --json files).
• A branch: git diff --name-only main...HEAD.
• Working tree: git status --porcelain.
• CLI shortcut for a range: repowise risk main..HEAD scores a branch/PR range for defect risk directly.

Write the review around evidence

Lead with a risk level and the directive findings, each tied to a concrete file. Distinguish "will break" (a dependent outside the diff) from "worth a look" (a co-change or health regression). Don't pad with findings the tools didn't support.

Error handling

If get_risk errors or returns nothing, the MCP server may be down or the repo unindexed — say so and review from the raw diff, noting that Repowise context was unavailable. Suggest /prompts:repowise-init if the repo isn't indexed.