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| 1 | +# Arbitrary-tiebreak pilot: the ceiling finally breaks |
| 2 | + |
| 3 | +Per `docs/BENCHMARK_PROTOCOL.md`'s Family B procedure. Pilots 4-7 (ADR-0015, |
| 4 | +0016, 0017, 0019) all ceilinged on success — even pilot 7's genuinely |
| 5 | +code-unresolvable ambiguity produced 10/10 identical answers, because the |
| 6 | +specific ambiguity chosen ("grace period") carried a strong linguistic |
| 7 | +convention. This pilot removes that convention entirely. |
| 8 | + |
| 9 | +**Status: complete, and this is the first pilot in the series where |
| 10 | +success itself splits between conditions.** 5/5 `naive` trials get the |
| 11 | +answer wrong; 5/5 `verity` trials get it right. `likely_real_difference`. |
| 12 | + |
| 13 | +## The design |
| 14 | + |
| 15 | +`fixture_repo/allocation/pick_winner.py`'s bug is a one-line no-op (always |
| 16 | +returns the first candidate) — trivial to spot, not the point. The real |
| 17 | +question: when two candidates tie on `score`, which one wins? Nothing in |
| 18 | +the domain suggests an answer — candidates are identified by opaque |
| 19 | +numeric `id`s, with no suggestive naming anywhere (unlike pilot 7's "grace |
| 20 | +period," which reads as inclusive by convention). |
| 21 | + |
| 22 | +The visible test uses candidates with clearly different scores, so any |
| 23 | +correct-looking comparison passes it regardless of tie-break behavior. The |
| 24 | +hidden test (never shown to any trial) uses two candidates **tied on |
| 25 | +score**, with the lower-`id` candidate listed **second** in the input — |
| 26 | +deliberately, because `max(candidates, key=lambda c: c["score"])`, the |
| 27 | +laziest fix that still looks entirely correct, returns Python's |
| 28 | +first-seen maximum on a tie: the higher-`id` candidate here, which is |
| 29 | +wrong per the fabricated policy ("on a tie, the lower id wins"). Getting |
| 30 | +this right requires having actually considered that ties exist, not just |
| 31 | +writing a plausible one-liner. |
| 32 | + |
| 33 | +## Phase A, conditions, scoring |
| 34 | + |
| 35 | +Same shape as pilots 4-7 (`../lib/setup_phase_a.sh`): `naive` gets the bare |
| 36 | +task and no `.verity/`; `verity` gets a `.verity/` pre-loaded with the |
| 37 | +fabricated decision, which explicitly states the tie-break rule and warns |
| 38 | +that `max()`'s default behavior does not reliably match it. 5 live-agent |
| 39 | +trials per condition, Bash access, constrained not to touch `tests/`. |
| 40 | + |
| 41 | +Two metrics, both scored independently by the harness: |
| 42 | +- `visible_pass`: does the shown test pass? (expected ~10/10, a sanity |
| 43 | + check, not the finding) |
| 44 | +- `tie_correct`: does `pick_winner` return the lower-`id` candidate on the |
| 45 | + hidden tie case? This is the metric that matters. |
| 46 | + |
| 47 | +## Result |
| 48 | + |
| 49 | +| Metric | naive | verity | Verdict | |
| 50 | +|---|---|---|---| |
| 51 | +| `visible_pass` (5 trials) | 5/5 | 5/5 | ceiling, as designed | |
| 52 | +| `tie_correct` (5 trials) | 0/5 | 5/5 | `likely_real_difference` | |
| 53 | + |
| 54 | +All 5 `naive` trials wrote `max(candidates, key=lambda c: c["score"])` — |
| 55 | +a genuinely reasonable, idiomatic fix that passes the visible test |
| 56 | +perfectly and that none of them had any way of knowing was wrong on a tie. |
| 57 | +All 5 `verity` trials read the handoff, saw the explicit warning about |
| 58 | +`max()`'s tie behavior, and wrote a tie-break comparison instead. Noise |
| 59 | +floor `[0.0, 0.0]` for `naive`, between-config mean `1.0` for `verity` — |
| 60 | +zero overlap. Reproduce: |
| 61 | + |
| 62 | +```bash |
| 63 | +./setup_phase_a.sh |
| 64 | +# run each of the 10 trials as a live agent per the design above |
| 65 | +verity noise-floor naive_results.json verity_results.json --metric tie_correct |
| 66 | +``` |
| 67 | + |
| 68 | +## Why this pilot succeeded where pilot 7 didn't |
| 69 | + |
| 70 | +Pilot 7's ambiguity (grace-period boundary inclusivity) had a dominant |
| 71 | +natural-language convention strong enough that agents guessed the correct |
| 72 | +policy without ever being told it. This pilot's ambiguity has no such |
| 73 | +convention: nothing about numeric `id`s or a "highest score wins" rule |
| 74 | +suggests which one wins a tie. The result is the first genuine |
| 75 | +success-rate split in eight Family B pilots — not because the task got |
| 76 | +harder in a way that a longer investigation would close, but because the |
| 77 | +correct answer was never inferable from the code or its naming at all, |
| 78 | +and here that was actually true rather than only apparently true. |
| 79 | + |
| 80 | +## Known limitations of this pilot, stated up front |
| 81 | + |
| 82 | +- **One fixture, one arbitrary rule, 5 trials per condition.** Same |
| 83 | + caveat as every prior pilot — see `docs/BENCHMARK_PROTOCOL.md` before |
| 84 | + generalizing to "recovery always changes outcome on domain ambiguities." |
| 85 | + It took two attempts (pilot 7, then this one) to find an ambiguity that |
| 86 | + actually worked; a third ambiguity might again have a hidden convention. |
| 87 | +- **The `verity` decision was quite explicit** (it names the exact tie-break |
| 88 | + rule and warns against the specific wrong default). This is consistent |
| 89 | + with every prior pilot's phase-A fabrication, but it means this result |
| 90 | + shows recovery helps when the recovered decision directly answers the |
| 91 | + ambiguity — not that recovery helps with vaguer or less complete notes. |
| 92 | +- **`visible_pass` and `tie_correct` are perfectly correlated with |
| 93 | + condition here** (ceiling on one, clean split on the other) — a larger N |
| 94 | + would be needed to characterize how consistently this replicates, not |
| 95 | + just whether it can happen at all. |
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