pi/rtx5090/qwen3.8-flash-next-ud-iq4_xs-unsloth-v3.1

Straightforward: the failing test pinned the bug exactly (grade_letter used > instead of >= at the 800 boundary, so 800 fell through to C). One-line fix, tests green, checksum read off program output. Only mild ambiguity was whether 'inside the folder' meant the zip root or the grades/ subpackage, but output is identical either way.

I traced all five groups by hand first (parameter-scope TDZ on x=y, finally-block return overriding both continue and return, generator .return() leaving the iterator done, map() preserving holes so join emits an empty field, and two independent n+=2 closures) and my prediction matched node's output character for character. The trickiest bit was v2f: reasoning that the finally-return at i=1 wins over the try's return 9 while the i=0 finally still ran before the continue, giving '0127'. Having node locally made this a confidence check rather than a gamble.

15/15 lines match

Implemented the three rules in the stated order with a small regex parser plus integer part lists, and hand-checked every line against the spec before running it. The cases that actually bite are rule 2's 'fewer parts always wins even with zeros' (1.0 vs 1, 7 vs 7.0.0, 12-beta8 vs 12.0-beta8) because it deliberately contradicts the usual semver behaviour, and the interaction where rule 2 decides before suffixes are ever consulted (5.0.9-beta4 vs 5.0.9.0-beta4). Nothing blocked me; I am reasonably confident, though rule 2's wording 'equal after steps 1 and 2' left a moment of doubt about whether a suffix could rescue the shorter version - I took the explicit 'the suffixes are ignored' sentence at face value.

Crash was exactly where the traceback said: vat.is_exempt did a dict lookup CATEGORY_KIND[cat] over a whitelist of three categories, while the README says the exemption rule is binary - only 'books' is exempt, everything else is taxed. One-word fix to .get(cat, 'taxed'), which also keeps the sample checksum 5c9fff4e intact, so it was clearly the intended change. Routine and satisfying; the only thing I'd flag is that the whitelist style invites the same bug again for regions/rates, though those already use .get correctly.

Feature request was precise and the worked example was the real spec: I checked my reading against it before writing code (US 28.99 -> net 2899 + 350 fee = 3249, tax (3249*11+50)//100 = 357, gross 36.06) and my first implementation reproduced both expected report lines exactly, which is strong evidence the fee belongs inside net and inside taxable. Kept order_tax's fee argument defaulted so the existing tax tests still pass; the existing 15 tests stayed green and the sample checksum moved off 6af5103c as the prompt said it should. Slight uncertainty remains on whether 'below 3000' is strictly less-than (I used <, so the 3000 EUR order pays nothing) - the example's EU line confirms that boundary.

Hardest of the three 'fix the project' tasks so far because nothing points at the bug - all 15 tests were green by design, so I had to read every module against the README. The giveaway was in the data: sample.csv contains 'BOOKS' and 'Books' categories, and tax.skips_tax did CATEGORY_KIND.get(category) without lowering, so capitalised books got taxed while the README says category case does not matter. One-line fix and the sample checksum jumped from 59f3fa7c to the README's 46954682, which is the strongest confirmation this kind of task offers. I also walked real.csv's category/region/currency distributions to be sure it holds no further surprises the sample never exercises (lowercase currencies and unknown categories are already handled correctly), so I am fairly but not totally confident real.csv has no second, unexercised violation.

The 'far cause' framing was accurate - the bug is nowhere near the reported symptom. I read every module against the README and the one deviation was ingest.to_record defaulting a blank qty to 0 instead of 1. It hid in the sample because sample.csv happens to contain no blank-quantity rows at all (26 in real.csv), which is exactly why the README checksum still passed. Best part of this challenge was the built-in check: after the fix the US 2026-03 USD group came out at 177071.39, matching finance's ledger to the cent, so I am confident rather than merely hopeful.

Hardest of the README-fix tasks: the issue said 'there may be more than one cause' and there were three, and they had to interact to produce those three numbers. (1) money.DECIMALS had JPY:2 with a compensating '//=100' hack in to_minor - so parsing was right but formatting printed 36243.14 for a yen amount, which is what tipped me off; (2) tax used round(taxable*rate/100) instead of the README's (taxable*rate+50)//100, i.e. banker's rounding on a float instead of integer half-up; (3) revisions.keep_latest ordered revisions by comparing the raw ts STRINGS, so a '+09:00' revision could beat a later UTC instant. Fixing all three reproduces finance's ledger exactly on all three quoted groups (3743814 / 708864.84 / 99675.43) and leaves the sample checksum 6bd686b9 untouched, which is consistent with the sample exercising none of them. I verified with a script that the ts-string dedupe really diverges on 30 rows and blank-qty rows exist, so I am not carrying a fourth undiscovered bug - though I cannot rule one out for groups finance never quoted.

Fun one - four separate quadratic/hot-path sins: dedupe_events did list.index() on a growing list of event_ids (O(n^2)); attach_plans linear-scanned the whole user list for every event (1e6 x 2e5); leaderboard recomputed max() over every user after every single event; and peak_live asked 'how many sessions are live at t' by scanning all sessions for each session start. I fixed each with the standard equivalent (dict index, plan dict keeping the first U line, incremental argmax that only ever moves to the just-updated user, and a closed-interval sweep line where starts are added before ends that merely tie). Verification was the part I cared about: sample still prints 463ca0ff, and I kept the original package side by side and diffed full reports against it on two 25k/40k-event logs - byte identical, 25.0s -> 0.07s. Big log now runs in ~4.7s. Slight residual risk that some pathological case the sample and my two random logs missed would diverge, but each rewrite is a provably-equivalent algorithm rather than a heuristic.