pi/rtx5090/qwen3.8-flash-next-ud-iq4_xs-unsloth-v3.1-strata0210

Straightforward: the failing test pinned the bug exactly - without_lowest sorted the caller's list in place, so it mutated DATA and corrupted the later class-average line. Fixed with a sorted copy; all 5 tests pass and the checksum prints cleanly.

Tracing semantics mostly went smoothly, but Array.prototype.join turning undefined into an empty string nearly caught me out: I had 77/undefined/1 in my head from the sloppy-mode arguments mapping and only caught it by actually running the snippet in node. Generator return()/throw() and the integer-key ordering were familiar.

15/15 lines match

Implementing the ordering rules was routine; the only real decision was how to combine rules 2 and 3 - I zero-padded the numeric parts so 1-0 and 1 count as numerically equal, then only consulted the _beta suffix when padding had not already decided. Cases like 7-1 vs 9 (decided on the first part, not length) and 9-1-1 vs 9-1-1-0-0 (length difference that padding cancels) are the ones the spec seems designed to catch, and I checked those by hand as well as by code.

The KeyError was honest enough: CATEGORY_KIND was a lookup table where the README describes a default rule, so any category outside the three hard-coded ones blew up. I replaced the table lookup with the rule itself (only 'books' is exempt). Slight unease because those 'fix the crash' tasks sometimes hide a second, quieter bug, but the sample still prints the README's 5ab8be4c after my change and all 15 unit tests pass, so the fix looks local.

The example in the request was the useful part - it pinned down two ambiguities I would otherwise have guessed at: the 1200/350 thresholds are in minor units whatever the currency, and an order landing exactly on 1200 pays nothing. I threaded a fee parameter into order_tax so the fee is added to taxable before the single per-order rounding, and kept order_tax's third argument optional so the existing tests still pass. The example.csv reproduced both expected lines exactly, and the sample checksum moved off e43aa0fa as the request said it would.

The tell was order_tax using round(taxable*rate/100) instead of the README's (taxable*rate+50)//100: Python's round() is banker's rounding on a float, so exact halves went the wrong way. The unit tests only used cases where both agree, which is exactly why they passed. Swapping in the integer formula moved the sample from 065e8cf2 to the promised 2497244d on the first try, so I am fairly confident that was the only deviation, though I did also re-read the revision tie-break, offset parsing and blank-field defaults for a second, quieter bug and found nothing.

The 'far cause' label fit: the symptom was a group total 3391.16 short, which reads like a tax or grouping bug, but it was actually a single character in the CSV reader - blank qty fell back to 0 instead of README's 1, so 27 rows in real.csv priced to zero net and paid no tax. It is invisible on sample.csv because that file happens to have no blank quantities, which is also why the README checksum stayed put. The ledger figure for EU 2026-01 EUR reproduced exactly after the fix, so I am confident.

This one was genuinely interacting, three separate README violations compounding. (1) currencies.py had JPY at 2 decimals with a hidden 'minor //= 100' compensation in to_minor, so yen amounts were built right but printed 100x small - that alone explains APAC 2025-07 exactly. (2) dupes.keep_latest kept the first row per (order_id,sku) and ignored instants entirely, so superseded revisions were priced - that drives most of US 2025-07 and part of APAC 2025-06. (3) duties.order_tax rounded per line instead of once per order, worth a few yen/cents. I fixed all three, and every one of the three ledger figures then reproduced exactly, while the sample checksum stayed 20e4f1e1 - which reassured me the sample simply never exercised those paths rather than that I had broken something the README wanted.all three ledger figures reproduced; sample checksum unchanged

The algorithmic shape did most of the work: membership joined users to events with a linear scan per event (200k users x 890k events), coverage counted distinct pairs by testing membership in a growing list, peak_live rescanned every session for every session, and figures re-scanned the whole event list for each long session. Fixing those four took the 1M-line run from 'hours' to 5 seconds. The one change I was not entitled to make blind was replacing the long-session event count with len(session.events); I proved it out first by brute force with binary search over each user's timestamps on the real big.log (139125 long sessions, no mismatch), and I also diffed the whole report against the untouched original on three medium logs and on the sample, which still prints f8a278d6.

Reconstructed the X16 ISA from the 8 probe traces and wrote an emulator; probe1 reproduces its whole 11477-step trace. Ran target1 to its halt (9727 steps, 345 port-0 bytes). Ops this target needed that are not in any fully-matching probe: 98 (my model: Rb = Rb - Ra + C, SBC-style), 82 (byte load with the same mode-displacement addressing as 9f/db, zero-extended), 7e (store byte of R_low at [R_high], R_high += 1 - confirmed from probe7 memory writes). Residual risk: 98's carry/overflow flags and 82's zero/sign extension.

wrong answer

Same emulator as target1 (probe1 fully reproduced). Target2 halts cleanly after 171195 steps and prints a long decimal expansion plus hex words. Inferred ops used: 98 (SBC-style), 82 (mode-displacement byte load), 62 (no observable effect in any trace; treated as a no-op/hint).

wrong answer

Same emulator; target3 halts after 9964 steps. Main unresolved op here is 6d (writes only flags; my flag model fits part but not all of the probe data), so one branch after a 6d may be wrong. Everything else used (21 RCR by imm4, 94 RCL by imm4, 5a signed bitfield extract width/lo in byte 3, 43/65/a1 shifts by Ra&15, 36 CLC, 93 STC, fd NEG, 55/66/b9 imm logic) is verified against probe traces.

wrong answer

Same X16 emulator (probe1 fully reproduced, probes 2/3/4/5 reproduce until an unresolved flag rule). For this target the decisive choice was opcode f7 (1-byte, no register/memory/port/flag effect observable in any trace): with f7 treated as a plain hint/NOP the program runs to its halt in 3181 steps; with the alternative 'f7 latches a flags-freeze mode' hypothesis (suggested by the anomalous INC/DEC flag behaviour in probes 6-7) it dies in a routine prologue, so I went with NOP.

Same emulator; target5 halts after 1702 steps. Key finding: opcode 18 is a byte store using the mode/displacement encoding of db/9f/82 (mode 8 = absolute) - the program self-patches code at 0x0480 with it, so this had to be right to halt at all. Also c4 = call via a vector table at 0xFB40 (base confirmed in probe5 and in target5's image), 5f = far return restoring flags, 28 = JSR via register.

wrong answer

Weakest of the six: this target is the one that leans on opcode ef, which I could not identify. ef is 2-byte, (src<<4)|dst, always writes dst, and its value is not any level-1 or level-2 expression of (Rb, Ra, imm, C) - I searched affine mod 2^16, GF(2)-linear, multiply-xor and 60+ op pairs; it also survives the (0,0) case producing 0x2ea3, i.e. it behaves like a PRNG/hash step (in probe8 it drives a random-looking chain 0x74c3 -> 0xb58f -> 0x4e0f ...). I therefore ran the target with ef approximated as a register copy (R_dst = R_src), which is the variant whose output is structurally plausible (sorted hex words + a digit line) - with ef as a no-op the output degenerates to one repeated value. Everything else in the target (4a/9f/db loads, e1 MUL, c0 ADD-imm, 02 OR-imm, 8d/35 call/ret, a3 Jcc, 19 SUBI, 55 ANDI, c1 OUT, ab/c8 INC/DEC) is verified against probe traces.