Turn a PR review into a repo-specific checklist Copilot Chat actually runs against the diff

You are reviewing a pull request in this repository using Copilot Chat, with the PR's diff open or referenced via #file so you have the actual changed lines in context, not a description of them.

PR CONTEXT
Adds rate limiting to the /api/checkout endpoint after last week's incident where a retry loop from a client bug hit it 40,000 times in an hour.

RISK AREAS TO WEIGHT MOST HEAVILY
Whether the rate-limit key is scoped per-user or per-IP (per-IP would break for users behind a shared corporate proxy), and whether the 429 response includes a Retry-After header.

HOUSE CONVENTIONS THIS DIFF MUST FOLLOW
All new middleware must be registered in middleware/index.ts, not imported ad hoc in the route file; error responses must use the shared ApiError class.

BLOCKING VS. NITPICK RULE
Anything that could let a request bypass the rate limiter entirely is blocking; naming, comment style, and import order are nitpicks only.

FILES OUT OF SCOPE FOR THIS REVIEW
package-lock.json and any file under generated/ that changed only because of a dependency bump.

STEP 1 — SCAN FOR BLOCKING ISSUES FIRST
Go through the diff once looking only for issues that match the blocking criteria above — do not surface a style nitpick in this pass even if you notice one, since mixing severities in one list is how a genuine blocker gets buried under six formatting comments and skimmed past. For each blocking issue, cite the exact file and line range from the diff you were shown, not a paraphrase of what the file probably does — if you are inferring behavior from a function name rather than reading its body, say so explicitly rather than presenting a guess as a finding.

STEP 2 — CHECK THE RISK AREAS SPECIFICALLY
For each item under RISK AREAS, state explicitly whether this diff touches it at all. If it does not, say so in one line and move on — do not manufacture a paragraph of analysis about a risk area the diff never goes near just to look thorough.

STEP 3 — HOUSE CONVENTIONS PASS
Check the diff against each house convention listed above as a yes/no, not a vibe. A convention either was followed in the changed lines or it was not; if you can't tell from what's in context, say which additional file you'd need to see rather than assuming compliance.

STEP 4 — NITPICKS, SEPARATED
List lower-severity suggestions in their own section, clearly separated from Step 1, and skip the files named as out of scope entirely — do not comment on a vendored or generated file just because it happened to appear in the diff.

OUTPUT FORMAT
1. Verdict: approve / request changes / needs discussion.
2. Blocking issues (file:line, what's wrong, what would fix it).
3. Risk-area check (one line per named risk area).
4. House-convention check (one line per convention, yes/no/can't-tell).
5. Nitpicks (separate section, optional to act on).