patch

name	patch
description	Propose a code patch for a finding. Produces a unified diff against the current HEAD plus a short rationale, written back as a finding note so the analyst can review, adjust, and open a PR themselves. The skill never pushes to the remote.
license	MIT
compatibility	Needs network access to the scrutineer API (http://host:port/api). Finding-scoped; runs against ./src at HEAD.
metadata	{"scrutineer.version":1,"scrutineer.output_file":"report.json","scrutineer.output_kind":"patch"}

patch

Propose a minimal code patch that fixes a confirmed finding. You are not shipping the fix; you are handing the analyst a starting diff and explaining what it does. The analyst reviews, edits if needed, and opens a PR by hand.

Workspace

• ./src — the repository at its current HEAD, on the default branch, writable
• ./context.json — has scrutineer.api_base, scrutineer.token, scrutineer.repository_id, scrutineer.scan_id, scrutineer.finding_id (required; this skill only makes sense finding-scoped)
• ./report.json — write the patch + rationale here
• ./schema.json — shape of report.json

What to do

1. Read ./context.json. If scrutineer.finding_id is missing, write {"error": "no finding_id in context.json; patch is finding-scoped"} to report.json and exit 0.

2. Fetch the finding: GET {api_base}/findings/{finding_id} with Authorization: Bearer {token}. Read location, cwe, trace, boundary, validation, rating. These five together tell you where the sink is, what the vulnerable input flow looks like, and what dangerous behaviour you need to stop.

3. Inside ./src, edit files to fix the finding. Constraints:

   • Minimal. Change only what the fix requires. Do not refactor surrounding code, rename variables, reformat unrelated lines, or upgrade dependencies unless the fix inherently requires it.
   • In place. Fix the sink where it lives. If the finding's location is pkg/foo/bar.go:42, that is where the patch should land (or at the nearest layer where a guard is sensible — e.g. the input validator that feeds the sink).
   • Consistent. Match the existing code style and idioms. If the codebase uses a specific sanitiser, validator, or helper for similar cases, reuse it. Do not introduce a new helper module for a one-off fix.
   • Safe. The patch must not break the reproduction's documented legitimate behaviour — only block the dangerous path. If you cannot tell where the dangerous path diverges from legitimate use, stop and refuse to patch (see "Refusing to patch" below for the {"error": ...} shape).
   • Include a test when practical. If the repo has a test suite that covers the vulnerable code path, add a regression test that would fail without your patch. If the repo has no tests, or the sink is in a place that is hard to cover, skip this and say why in rationale.

4. Once you have a working tree edit, generate a unified diff against HEAD:

   cd src
   git add -N .
   git diff HEAD -- . > ../patch.diff
   

   Read ../patch.diff (the workspace root, alongside report.json) and put its contents into report.json under the patch field. Do not commit; the diff is the artefact. If the diff is empty, something went wrong — do not write an empty patch. Write {"error": "patch produced no diff"} and exit 0.

5. POST a finding note summarising the patch: POST {api_base}/findings/{finding_id}/notes with:

   {
     "body": "Proposed patch in scan #{scan_id}.\n\nFiles changed: ...\n\n{short rationale}\n\nApply with: `git apply` the diff from the scan report.",
     "by": "patch"
   }
   

   The note lives on the finding page; the full diff lives in report.json and is viewable on the scan page.

6. Do not PATCH any editable fields on the finding. Specifically:

   • Do not set fix_commit — that field means a shipped upstream fix, not a proposal. The analyst sets it after their PR merges.
   • Do not set fix_version — same reason.
   • Do not touch status. Lifecycle transitions belong to the analyst.

7. Write ./report.json:

   {
     "patch": "diff --git a/pkg/foo/bar.go b/pkg/foo/bar.go\n...",
     "rationale": "Short prose — two or three sentences. What the guard is, why it blocks the trace, what legitimate input it still lets through.",
     "files_changed": ["pkg/foo/bar.go", "pkg/foo/bar_test.go"],
     "base_commit": "<HEAD sha from ./src>",
     "tests_added": true,
     "notes": "Optional: anything the analyst should know — a second sink you spotted but didn't patch, a style choice you weren't sure of, a test you couldn't write."
   }
   

   base_commit is the HEAD sha the diff applies to. The analyst needs this to git am or git apply cleanly — if they rebased since the scan, they know the patch may not apply and can regenerate.

Refusing to patch

Write {"error": "...", "rationale": "..."} and exit 0 in any of these cases — do not ship a bad patch:

• The finding prose is too thin (empty Trace, empty Validation). You need both to know where the sink is and what behaviour to stop.
• The fix is architectural (e.g. "rewrite this whole module to not shell out") rather than localisable. A patch skill proposes a surgical fix; larger changes are an issue comment for the maintainer, not a diff.
• The codebase is in a language or framework you cannot confidently edit without risking regressions. It is better to say so than to produce a plausible-looking but wrong patch.
• The finding has already been fixed upstream. Check git log -- {location} — if a recent commit looks like it addressed the sink, surface the SHA in notes and refuse to duplicate.

Constraints

• Do not push. Do not commit. Do not open a PR. The scrutineer workspace is ephemeral and isolated; your diff is the only thing that survives the scan.
• Do not add new dependencies. If sanitisation or escaping is needed, reuse a helper the codebase already imports. A patch that needs a new top-level dep almost always means the fix is in the wrong place.
• Do not edit the lockfile, go.sum, Gemfile.lock, package-lock.json, Cargo.lock, etc. unless you also changed the manifest that owns it. Stray lockfile churn makes diffs hard to review.
• Do not touch files outside what the fix requires. CI config, docs unrelated to the fix, README — leave alone.