You:
Refactor @orders.ts with these goals:
1. Extract the discount calculation into a separate pure function
2. Replace the nested if/else block (lines 45-78) with a switch or map
3. Add TypeScript types for all function parameters and return values
4. Add JSDoc comments to each exported function

Constraints:
- Do NOT change any external behaviour — all existing tests must still pass
- Do NOT rename any exported functions (other modules import them)
- Do NOT add new dependencies

After the refactor, list every change you made and why.

You:
Write Jest tests for @cart.ts. Use describe/it blocks.

Cover these scenarios:
- Happy path: add item, update quantity, remove item, calculate total
- Edge cases: empty cart, quantity of 0, negative quantity
- Error cases: invalid product ID, product not found, stock exceeded
- Boundary: maximum cart size (50 items), maximum quantity per item (99)
- Concurrency: two simultaneous addItem calls with the same product

For each test:
- Use descriptive test names that explain the expected behaviour
- Include arrange/act/assert comments
- Use test fixtures, not inline data
- Mock the database layer using jest.mock()

You:
Review these files for our upcoming PR:
@webhook-handler.ts @order-processor.ts @types/order.ts

Review criteria (check each):
1. SECURITY: Input validation, authentication, injection vulnerabilities
2. ERROR HANDLING: Are all failure modes handled? Are errors logged?
3. PERFORMANCE: N+1 queries, unnecessary allocations, O(n^2) algorithms
4. TYPES: Are types complete? Any implicit `any`?
5. READABILITY: Clear naming, appropriate comments, no magic numbers
6. TESTS: Is the code testable? What test cases are missing?

For each issue found, provide:
- Severity: Critical / High / Medium / Low
- File and line number
- Problem description (one sentence)
- Suggested fix (code snippet)

At the end, give an overall "merge readiness" rating:
Ready / Needs Minor Changes / Needs Major Changes / Block

You:
Add a "wishlist" feature to ThreadCo's store:
1. @types/product.ts — add a WishlistItem type
2. @api/wishlist.ts — create GET/POST/DELETE endpoints
3. @components/ProductCard.tsx — add a heart icon toggle
4. @__tests__/wishlist.test.ts — write tests for the API endpoints

Use the same patterns as @api/cart.ts and @components/CartButton.tsx
for consistency. Include error handling. Do not modify any existing
tests or endpoints.

Claude reads all referenced files, creates/edits 4 files, and
maintains consistency across all of them because it can see the
existing patterns.

You (in Claude Code chat):
Review @webhook-handler.ts for security issues.
Focus on: input validation, authentication, and anything
that could be exploited by a malicious POST request.

Rate each issue: Critical / High / Medium / Low.

Claude responds:
CRITICAL: Missing Stripe signature verification (line 14).
Any HTTP client can send fake webhook events. Add:

  const sig = req.headers['stripe-signature'];
  stripe.webhooks.constructEvent(payload, sig, process.env.STRIPE_SECRET);

HIGH: Raw body not preserved — signature verification will fail
because body-parser is consuming the stream before verification.
...