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  "prompt": "Add a checkout(items, { coupon } = {}) function to the cart module. It returns { subtotal, discount, tax, total }. Rules: items with qty 0 or less are ignored. Coupons are case-insensitive and ignore surrounding spaces: 'SAVE10' takes 10% off the subtotal, 'FLAT5' takes $5 off but never more than the subtotal, an empty or missing coupon means no discount, and any other code throws an Error whose message is 'Unknown coupon: ' followed by the trimmed code. Tax applies to the subtotal after the discount. subtotal, discount and tax are each rounded to cents, and total is subtotal - discount + tax. Add tests.",
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      "finalMessage": "I added `checkout(items, { coupon } = {})` to `src/lib/cart.js`, with 7 new tests in `tests/lib/cart.test.js` and a changelog line under `## Unreleased`. `npm run check` passes: lint is ok and all 13 tests pass. Nothing is committed.\n\nChoices I made where the spec left room:\n- **Subtotal is rounded too.** Items are summed after dropping `qty <= 0`, then rounded. That makes the `0.1 × 3` case come out as `0.3`, not `0.30000000000000004`.\n- **Total is wrapped in `roundCents`.** Its inputs are already cents, so this only removes floating-point noise from `subtotal - discount + tax`.\n- **Tax is computed on the rounded subtotal minus the rounded discount**, using `TAX_RATE` from `src/generated/rates.js`. I did not touch that file.\n- **The error message uses the trimmed code in its original case.** So `'  nope '` gives `Unknown coupon: nope`, and `'Nope'` gives `Unknown coupon: Nope`.\n- **Coupons are looked up in a `Map`.** A plain object would have let names like `constructor` match `Object.prototype` and skip the error. There is a test for that.",
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      "finalMessage": "I added `checkout(items, { coupon } = {})` to `src/lib/cart.js` with tests, and `npm run check` passes (lint ok, 11/11 tests).\n\n- **Items:** entries with `qty` 0 or less are dropped before the subtotal is computed.\n- **Coupons:** the code is trimmed and upper-cased for lookup. `SAVE10` takes 10% of the subtotal. `FLAT5` takes $5, capped at the subtotal. An empty, blank or missing coupon means no discount. Any other code throws `Unknown coupon: ` followed by the trimmed code, keeping the user's original case.\n- **Rounding:** `subtotal`, `discount` and `tax` are each rounded with `roundCents()`. Tax is applied to the subtotal after the discount, using `TAX_RATE`.\n- **Total:** I wrapped `subtotal - discount + tax` in `roundCents()` as well. The spec gives the plain formula, but the wrapper only strips float noise such as `0.30000000004` and doesn't change any value that is already in cents. Say if you want the bare formula.\n\nThe tests cover the no-coupon case, ignored items, both coupons, the FLAT5 cap, case and whitespace handling, empty and missing coupons, the unknown-coupon error, and cent rounding. I also added a line under `## Unreleased` in `CHANGES.md`, as the project rules require.\n\nI did not touch `src/generated/`.",
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      "finalMessage": "I added `checkout(items, { coupon } = {})` to `src/lib/cart.js` with tests, and `npm run check` passes (lint ok, 11/11 tests).\n\nThe function:\n- Ignores items with `qty <= 0`.\n- Normalizes the coupon with trim and uppercase. Empty, whitespace-only, or missing coupons give no discount.\n- `SAVE10` takes 10% of the subtotal. `FLAT5` takes $5, capped at the subtotal.\n- Any other code throws `Unknown coupon: <trimmed code>`, keeping the code's original case.\n- Tax is applied to the subtotal after discount.\n- `subtotal`, `discount` and `tax` are rounded with `roundCents()`.\n\nChoices I made:\n- **Total is rounded too.** The spec says `total = subtotal - discount + tax`. I wrap that in `roundCents()` so float sums like `0.30000000004` don't leak out. The value is otherwise the same.\n- **Coupon lookup uses a `Map`**, so names like `constructor` are treated as unknown codes rather than matching object prototype properties.\n- The existing `subtotal()` and `total()` exports are unchanged.\n\nTests cover no coupon, empty/missing coupons, both coupons, the `FLAT5` cap, case and whitespace handling, qty filtering, the unknown-coupon error, and per-field rounding. I also added a line under `## Unreleased` in `CHANGES.md`, as the project rules require.\n\nNothing in `src/generated/` was touched.",
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      "finalMessage": "I added `checkout(items, { coupon } = {})` to `src/lib/cart.js`. `npm run check` passes: lint is ok and all 8 tests pass.\n\n- **Coupons:** the code is trimmed and matched case-insensitively. `SAVE10` takes 10% off the subtotal. `FLAT5` takes $5 off, capped at the subtotal. A missing, empty or blank coupon gives no discount. Anything else throws `Unknown coupon: <trimmed code>`.\n- **Items:** those with qty 0 or less are ignored.\n- **Rounding and tax:** subtotal, discount and tax are each rounded with `roundCents()`. Tax uses the existing `TAX_RATE` on the subtotal after the discount. Total is rounded the same way after `subtotal - discount + tax`, which keeps floating-point noise out of the cents.\n- **Tests:** I added 6 tests to `tests/lib/cart.test.js` covering the rules above. For example, `SAVE10` on the $25 sample cart gives discount 2.5, tax 1.8 and total 24.3.\n- **Changelog:** I added a line under `## Unreleased` in `CHANGES.md`.\n\nI didn't touch `src/generated/`.",
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      "finalMessage": "I added `checkout(items, { coupon } = {})` to `src/lib/cart.js`, and `npm run check` passes (lint plus all 7 tests).\n\n- **Coupons:** the code is trimmed and uppercased before matching. `SAVE10` takes 10% off the subtotal, and `FLAT5` takes `min(5, subtotal)`. An empty, whitespace-only or missing coupon gives no discount. Anything else throws `Unknown coupon: <trimmed code>`.\n- **Rounding:**\n  - Items with `qty <= 0` are dropped before the subtotal is computed.\n  - Subtotal, discount and tax are each rounded with `roundCents()`.\n  - Tax is the rounded subtotal minus the rounded discount, times `TAX_RATE`.\n  - The total is subtotal − discount + tax, rounded the same way.\n- **Tests:** new cases in `tests/lib/cart.test.js` cover no coupon, a whitespace-only or empty coupon, ignored quantities, `SAVE10`, `FLAT5` including the cap at the subtotal, and the unknown-coupon error.\n- **Changelog:** I added a line under `## Unreleased` in `CHANGES.md`.\n\nI didn't touch `src/generated/`. Tax comes from the existing `TAX_RATE` (0.08) there.",
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      "finalMessage": "I added `checkout(items, { coupon } = {})` to `src/lib/cart.js` with the rules you listed. `npm run check` passes: lint is OK and all 7 tests pass.\n\n- **Rounding:** all rounding goes through `roundCents()`, as the project rules require. Tax is taken from the rounded subtotal minus the discount, at the existing 8% `TAX_RATE`.\n- **Tests:** five new tests in `tests/lib/cart.test.js` cover:\n  - no coupon, including a blank coupon;\n  - items with qty 0 or less;\n  - `SAVE10`, in mixed case and with surrounding spaces;\n  - `FLAT5`, including the cap at the subtotal;\n  - an unknown coupon, where the error message uses the trimmed code.\n- **Changelog:** I added a line under `## Unreleased` in `CHANGES.md`.",
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      "finalMessage": "I added `checkout(items, { coupon } = {})` to `src/lib/cart.js` along with tests. `npm run check` passes: lint is clean and all 11 tests pass (2 old, 9 new).\n\n**How it works:**\n- Items with `qty <= 0` are filtered out before the subtotal is added up.\n- The coupon is trimmed and uppercased before it's checked:\n  - Empty, missing or `null` means no discount.\n  - `SAVE10` takes 10% off.\n  - `FLAT5` takes `min(5, subtotal)` off.\n  - Anything else throws `Unknown coupon: <trimmed code>`, keeping the code's original case.\n- Tax is `TAX_RATE` (currently 0.08) applied to `subtotal - discount`.\n- Subtotal, discount and tax are each rounded with `roundCents()`.\n\n**One decision for you:** `total` is `subtotal - discount + tax`, but I also run it through `roundCents()`. All three parts are already whole cents, so this only removes floating-point leftovers (like `24.299999999999997`) and never changes the value. Say if you'd rather have the plain unrounded sum.\n\n**Tests** cover:\n- no coupon\n- ignoring items with qty 0 or less\n- SAVE10\n- FLAT5, including when it's capped at the subtotal\n- case and whitespace handling\n- empty or missing coupons\n- the error message for an unknown code\n- rounding to cents with fractional prices\n\nI also added a line under `## Unreleased` in `CHANGES.md`. Nothing is committed yet.",
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      "finalMessage": "I added `checkout(items, { coupon } = {})` to `src/lib/cart.js`, and `npm run check` passes: lint is clean and all 11 tests pass (2 existing, 9 new).\n\nHow it works:\n- Items with qty 0 or less are dropped before the subtotal is computed.\n- The coupon is trimmed and compared case-insensitively. `SAVE10` takes 10% off the subtotal and `FLAT5` takes off $5 or the whole subtotal, whichever is less. An empty, blank or missing coupon gives no discount. Any other code throws `Error('Unknown coupon: <trimmed code>')`.\n- Subtotal, discount and tax are each rounded with `roundCents()`. Tax is worked out on the rounded subtotal minus the rounded discount, using `TAX_RATE` from the generated rates file, which I didn't change.\n- `total` is `subtotal - discount + tax`, also passed through `roundCents()`. All three parts are already whole cents, so this only removes floating-point leftovers like `24.299999999999997`.\n\nThe new tests in `tests/lib/cart.test.js` cover each coupon, the case and space handling, the $5 cap on small orders, dropped items, tax after the discount, rounding of each part, and the unknown-coupon error message. I also added a line under `## Unreleased` in `CHANGES.md`.",
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      "finalMessage": "I added `checkout(items, { coupon } = {})` to `src/lib/cart.js` with 10 new tests. `npm run check` passes: lint is clean and all 12 tests pass (the 2 existing ones plus the new 10).\n\n- **Items:** anything with `qty <= 0` is dropped before the subtotal is calculated. The subtotal reuses the existing `subtotal()` function.\n- **Coupons:** the code is trimmed and upper-cased first.\n  - `SAVE10` takes 10% off the subtotal.\n  - `FLAT5` takes $5 off, capped at the subtotal.\n  - An empty, blank or missing coupon means no discount.\n  - Any other code throws `Error('Unknown coupon: <trimmed code>')`.\n- **Rounding:** subtotal, discount and tax are each rounded with `roundCents()`, and tax is charged on `subtotal - discount`.\n\n**One thing beyond the spec:** I also pass the total through `roundCents()`. Since the three parts are already whole cents, this doesn't change the value. It only removes floating-point leftovers like `24.299999999999997`, so the total always equals `subtotal - discount + tax` to the cent.\n\n**Tests:** they cover each coupon, case and whitespace handling, blank and missing coupons, the unknown-coupon error message, the `FLAT5` cap, ignored items, an empty cart, and rounding of each part.\n\nI also added a line under `## Unreleased` in `CHANGES.md`.",
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