pi/rtx5090/qwen3.8-flash-next-ud-iq4_xs-unsloth-v3.1-basalt020

Routine: one test failed loudly (hold_units reserved qty-1 because of range(qty - 1)) and the fix was an obvious off-by-one. I did pause on whether pick_fifo ignoring the reserved count was a second bug, but the tests and docstring treat reservations as a separate counter, so I left it alone and just made the suite pass.

Ran it in node rather than trusting my head, which saved me: I first expected v4 to end in :16 (a fourth getter call) but the last expression reads v4o.n, not v4o.next, so it is 13. I also nearly wrote 84/undefined/1 for the second v5f call, forgetting that Array.join renders undefined as an empty string. Pleasantly nasty puzzle; my only residual doubt is whether the expected answer includes the trailing newline that console.log adds.

15/15 lines match

Straightforward bracket arithmetic; the only real decision was the tie rule, and the spec pinned it down (every subtotal ends in 0 or 5 because all rates are multiples of 5, so round-half-up is the same as rounding up to the next multiple of 10). I hand-checked a few rows against the script output. Nothing felt like a trap here.

Similar shape to the last one but easier: the traceback pointed straight at to_record, which looked the currency up in DECIMALS raw instead of normalising it, so ' JPY ' blew up even though the README promises case- and space-insensitive currencies. One-line fix with strip().upper(), and the sample checksum then matched the README's 9a909095, which is a decent signal I did not break or miss anything.

Feature work was mechanical once I found the one place tax exemption is decided (duties.exempt_category): I threaded an extra_exempt frozenset from an argparse --exempt flag down through group_orders/finalize_order into order_tax, lower-casing both the CLI names and the file categories. I verified the three things that mattered: sample checksum unchanged without the flag (7bcf6ae7), the issue's example reproduces exactly (38.88 -> 36.00), and ' GARDEN , General ' gives the same checksum as Garden,general. Blank categories become 'general' per the README, so --exempt general exempts them too, which I think is right but is the one judgement call here.

Trickiest of the bug-hunt set so far because nothing fails: tests pass and the report looks plausible. I read the README line by line against the modules and the only rule that the code contradicted on paper was rule 8's 'on a tie, the greater order_id' — rollup.summarize used a bare > on instant, so the first-seen order won a tie. I sanity-checked that hypothesis by brute force: I built a harness that patches each candidate deviation (tie-break, dedupe direction, discount rounding, tier boundaries, price rounding) and reruns the sample, and only the tie-break patch reproduced the README's 9d593382, which is a good sign there is no second bug hiding.

The misleading part was that the symptom (a wrong gross in one report group) is nowhere near the cause. I diffed the pipeline against the README rule by rule and the ingest step had qty = int(row['qty'] or 0), so all 27 blank-quantity rows in real.csv were priced as zero units instead of 1 — sample.csv has no blank quantities, which is why the sample checksum looked fine and no test caught it. The ledger figure was a great check: after the one-character fix the EU 2026-09 EUR group prints exactly the 445305.76 finance expected, and the sample checksum and unit tests are unchanged.

Three separate bugs feeding into the same totals, which is what made this hard: currencies had JPY registered as 2-decimal with a compensating //=100 hack inside to_minor, so every JPY group was printed 100x too small with a spurious .00; the discount tiers used > instead of >= so qty of exactly 15 or 31 got the wrong rate; and tax used Python round() on a float instead of the README's (taxable*rate+50)//100, which drifts on half-cent ties and on banker's rounding. I found them by reading each module against its README rule rather than by chasing the numbers, then used the three ledger figures as the test — all three now match exactly, the sample checksum is still 55d6c081 and the tests still pass. I am only mildly worried there could be a fourth bug in a group finance did not look at, since a deliberately clean sample checksum is weak evidence.

Fun one. The slowness was four accidental O(n^2)s: percentile did a hand-rolled selection sort, stats_by_plan called session_size which rescanned every event for every session (a session already holds exactly its own events, since a user's sessions are disjoint time ranges), kind_coverage did membership tests against a list of pairs, and top_user_changes recomputed max over all users after every event — that last one only needs a compare against the user it just bumped, because totals never decrease. I verified equivalence rather than trusting the reasoning: identical output on the sample (caf4b6ba) and on two independently seeded 60k/150k logs versus the unmodified package, plus a 300-case fuzz test of the leader rewrite. Full 1M-event log now finishes in about 5 seconds.

Rebuilt the X16 CPU from the 8 probe traces (emulator in /tmp/cpu/emu.py reproduces probes 1,2,4,5,8 step-for-step, 100% of registers/flags/memory-writes/port-0 output; probes 3,6,7 pass up to a single step each, all three of which sit immediately after an opcode I could not pin down). Decoded: 1-4 byte instr lengths, BE immediates / LE stack, R7=SP, call 9B + ret 3B, trap 93 (pushes return addr then flag byte N=bit0,V=bit1,C=bit5,Z=bit6, jumps to word[n] of the vector table at 0xFC80) and 4D = return-from-trap restoring the flags, 10 = call indirect, 6C = CMP reg,imm16, 06 = CMP reg,reg (C=borrow), 7A/23/DB = mov/add/sub imm16, 7D/7B = add/sub reg, 8C/85/96/18 = or/xor/and/not, 8D mul, 51 divmod, FB shl by R[n], 1F shr by R[n], 0F rcl by imm, 5E rcr by imm, 0B dec, DA/F1 push/pop, 59/36 byte load/store (post-increment), 2C/6B word load/store (post-increment), B1/2F/5F load/store with 16-bit displacement (bit7 of operand byte = absolute addressing), D4 byte load with displacement, 79/2C addressing, 60 mov, 4E out port, BF inc, D1 clc, BC 16-condition relative branch (offset from end of instruction), DE halt. Ran target1 to the halt instruction with no unimplemented opcode on its path (10962 steps): port-0 output is a readable Vigenere plaintext (key M=16 B=9 E=8 L=8 K=7), so the run is verified self-consistently. FNV-1a 32 over the 398 port-0 bytes = 59c717e6, final R0 = 0x9f46.

wrong answer

Same X16 emulator as target1 (now reproducing probes 1,2,4,5,7,8 completely, step-exact incl. flags/memory writes/port-0 output; probes 3 and 6 pass except one step each, both immediately after an opcode still not pinned down). Opcodes added since target1: E9=AND reg,imm16; A4=OR reg,imm16; E3=ADD reg,sign-extended imm8 (C=carry-out of the 16-bit two's-complement add); 3D=NEG reg (C=1 if operand nonzero); D4=load byte with 16-bit displacement; D1=CLC; 18=NOT reg (clears V); BD and CA are genuine no-ops (verified: with them emulated as no-ops probes 1,2,4,5,7,8 still run step-exact, ~2600 executions). Target2 was executed to its halt instruction (157727 steps) with no unimplemented opcode on the path. Output: 99-digit decimal string + 8 hex words, final word = final R0 = a296. FNV-1a 32 over the 239 port-0 bytes = 326e97aa.

wrong answer

Same X16 emulator. Target3 runs 12752 steps and reaches its halt instruction; it exercises 8D (16x16 multiply: low word into R[lo], C=high-word nonzero, V=signed overflow), 26 (arithmetic shift right by count taken from a register), A1 (TEST: AND of two registers, flags only, result discarded), E3 (ADD sign-extended imm8), 3D (NEG), D1 (CLC), D8 (logical shift right of a register by an immediate bit count - Z/N updated, C/V untouched; note: probe7 contains D8 forms whose result I could not reproduce, so this opcode is the one residual risk in this target) and 58 (1-byte, sets C from bit 15 of R7 in all 37 probe occurrences - weakly determined, the second residual risk). Output = 259 bytes of hex words; last word = printed final R0 = caf9; FNV-1a 32 = 01afea27.

wrong answer

X16 emulator (probes 1,2,4,5,7,8 step-exact; probes 3 and 6 one step each off, both directly after an opcode not yet pinned down). Opcodes added for this target: 7F = read the status byte into a register (layout N=bit0,V=bit1,C=bit5,Z=bit6 - 5375/5375 trace cases), 8F = write the status byte from a register to the flags (5245/5251), A1 = TEST/AND of two registers, flags only, result discarded, 3D = NEG, E3 = ADD sign-extended imm8, E9 = AND imm16, A4 = OR imm16, 18 = NOT (clears V), CA and BD are true no-ops. Target4 runs to its halt instruction (3196 steps) with no unimplemented opcode executed on its path; port-0 output is 20 hex words whose last equals the printed final R0 = 5d30; FNV-1a 32 over the 109 output bytes = ec8e9f66.

Same X16 emulator (probes 1,2,4,5,7,8 reproduced step-exactly). Target5 runs to its halt instruction in 1888 steps with no unimplemented opcode executed on the path - it exercises the trap instruction 93 (push return address then flag byte with layout N=bit0,V=bit1,C=bit5,Z=bit6, jump to word n of the vector table at 0xFC80) and its return 4D (restores the flags, pops PC, R7+=4), 0F=RLC/rotate-left-through-carry by an immediate bit count, 5E=rotate-right-through-carry, FB=shift left by count in a register, 1F=shift right by count in a register, 51=divmod (quotient into R[lo], remainder into R[hi], C=remainder nonzero, divide by zero leaves registers and sets Z). Port-0 output (77 bytes) ends with the final R0 printed in hex = 574f; FNV-1a 32 = 2a4073b0.

wrong answer

Same X16 emulator. Target6 halts in 38479 steps, but it is the only target that executes opcode 0x77 (2-byte, dst = low nibble, source = high nibble) which I could not reverse: across 2849 probe occurrences it rewrites one register with a value that is affine over GF(2) in the destination register (leading rows new_bit0 = old_bit11, new_bit1 = old_bit11^old_bit12 - an LFSR/PRNG-like linear map) with a source-dependent additive term; it is not a shift, add, multiply, rotate, CRC-table form or FNV form. My run therefore treats 77 as a skip, so the three hex words and the R0 chain that pass through it are almost certainly wrong; everything else on the path (trap 93/4D, div 51, mul 8D, shifts, branches) is trace-verified. Reported values are from that run: FNV-1a 32 = e931a151 over the 104 port-0 bytes, final R0 = 16fe (self-printed by the program).

valid, band 1/3

Same plan for all three levels (one shot each). Cost model re-implemented from problem.md from scratch and cross-checked against the worked example there (1455 for the sample plan, leg rounding 11): distances are ceil(sqrt) of the squared grid distance, zone minutes exact via Fractions, toll = 25 per zone boundary crossing + 150 per out-and-back, 800 per vehicle, route time = drive + service with the earliest-departure/wait rule. Result: 51 vehicles, all 786 customers served exactly once, dist 16397 + toll 19197 + 51*800 = 223967. Independently validated by a separate checker (capacity, time windows, shift end, zone rules, every customer exactly once) - 0 errors. Method: sweep/greedy construction over shuffled unit orders with per-unit drop-order search, then iterated local search combining intra-route 2-opt/or-opt, inter-route relocate/swap, route elimination, 2-opt* and start-point polishing, run as 8 parallel randomised restarts of 160s slices. Trade-off note: a lower-toll plan with more route-cuts was preferred over raw distance because the per-vehicle fixed cost dominates; the search therefore spent most effort on route elimination. Residual risk: gold may sit below this cost; my best 8 restarts converged to 223967-231678 and no run beat 223967.

valid, band 1/3

Same plan for all three levels (one shot each). Cost model re-implemented from problem.md from scratch and cross-checked against the worked example there (1455 for the sample plan, leg rounding 11): distances are ceil(sqrt) of the squared grid distance, zone minutes exact via Fractions, toll = 25 per zone boundary crossing + 150 per out-and-back, 800 per vehicle, route time = drive + service with the earliest-departure/wait rule. Result: 51 vehicles, all 786 customers served exactly once, dist 16397 + toll 19197 + 51*800 = 223967. Independently validated by a separate checker (capacity, time windows, shift end, zone rules, every customer exactly once) - 0 errors. Method: sweep/greedy construction over shuffled unit orders with per-unit drop-order search, then iterated local search combining intra-route 2-opt/or-opt, inter-route relocate/swap, route elimination, 2-opt* and start-point polishing, run as 8 parallel randomised restarts of 160s slices. Trade-off note: a lower-toll plan with more route-cuts was preferred over raw distance because the per-vehicle fixed cost dominates; the search therefore spent most effort on route elimination. Residual risk: gold may sit below this cost; my best 8 restarts converged to 223967-231678 and no run beat 223967.

valid, band 1/3

Same plan for all three levels (one shot each). Cost model re-implemented from problem.md from scratch and cross-checked against the worked example there (1455 for the sample plan, leg rounding 11): distances are ceil(sqrt) of the squared grid distance, zone minutes exact via Fractions, toll = 25 per zone boundary crossing + 150 per out-and-back, 800 per vehicle, route time = drive + service with the earliest-departure/wait rule. Result: 51 vehicles, all 786 customers served exactly once, dist 16397 + toll 19197 + 51*800 = 223967. Independently validated by a separate checker (capacity, time windows, shift end, zone rules, every customer exactly once) - 0 errors. Method: sweep/greedy construction over shuffled unit orders with per-unit drop-order search, then iterated local search combining intra-route 2-opt/or-opt, inter-route relocate/swap, route elimination, 2-opt* and start-point polishing, run as 8 parallel randomised restarts of 160s slices. Trade-off note: a lower-toll plan with more route-cuts was preferred over raw distance because the per-vehicle fixed cost dominates; the search therefore spent most effort on route elimination. Residual risk: gold may sit below this cost; my best 8 restarts converged to 223967-231678 and no run beat 223967.