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). No LLM, no network. Prefer this in-MCP tool; it takes a revspec and diffs server-side, so you never shell out. Lead with directive and health_delta — what the change actually made worse. Findings the change wrote sort above pre-existing ones it only touched. Then risk_percentile (this change ranked against sampled recent commits by diff size and spread, not a bug predictor), stated in one line by diff_shape; include=["scales"] adds its review_priority tercile and classification label. The raw 0-10 score ranks 0.99 against lines added, so it sits behind include=["diagnostics"] rather than on the wire. 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 directive first: status, a headline naming what got worse, the reasons behind it and next_actions to run. health_delta carries the findings the change introduced or resolved. Then 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, or a directive.status of unknown, 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 per-file directive

Call get_risk in PR mode by passing the changed files:

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

The response carries its own directive block, per file rather than per change (distinct from get_change_risk's) — read it first, it's a few short lists:

• may_break — files/symbols that import their way to what changed but are not in the diff. Reachability, not a diff: it says these depend on the changed files, not that the thing they use changed. 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 tests the change needs, from the same selection repowise impacted-tests makes, with tests_to_run_why giving each one's reason (the changed file and its evidence, or "runs with every subset"). Check tests_run_all first: when it is true no smaller set can be vouched for, tests_run_all_reasons says why, and the list is only what to run first; recommend the whole suite. When it is false the list is the set to run. tests_to_run_basis is measured when stored per-test coverage decided a changed file and inferred when only the dependency graph or a rule did; say which. tests_status appears only when no selection could be made (timeout, config_invalid, unknown, ...), and then every test must run.

get_change_risk carries the same answer as impacted_tests: status (selected or run_all, or why nothing was selected), run_all, reasons, tests_to_run and why. include=["blast"] on get_risk adds pr_blast_radius, the fuller dossier behind the directive's lists.

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 "may 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.