# HeadOn vs Pattern at long range — LIVE gate

**Date:** 2026-09-24
**Branch:** `research/lead-targeting` · **commit:** `a82c864` · **binary sha256:** `9d20f530d6…` (one frozen binary, `git archive HEAD`)
**Session:** `/tmp/ab_headon` · 2 arms × 15 runs × 7 rounds = 210 rounds, `conc=8`
**Fixtures committed:** `headon_longrange_ab_report.txt` (ab_analyze), `headon_longrange_bands.txt`
(range-band), `headon_longrange_live_results.json` (per-run + per-band counts). Arms: `tools/ab/arms_headon.txt`.

## Direct answer

**NO. The no-lead static gun does not beat Pattern live, overall or in any long-range band.** It is
not close: HeadOn won **0 of 105 rounds** and dealt **14 dmg/run vs 279** (20× less), and at
**450+ px it hits 0.4% vs Pattern's 9.2%** (23× less). The offline ruler's headline — HeadOn has
lower aim error and a *better* hit proxy than Pattern at 300+ px — is **killed**. The offline ruler
was the only thing that predicted the opposite; this live A/B is the only thing that can confirm or
kill it, and it killed it.

## The `TR_PATTERN_RAD_SCALE` arms were skipped (the knob cannot express the lead hypothesis)

`common_libs/guns/pattern_matcher.nim` `applyRadial` moves the aim point **along the unchanged
bearing** `(selfX + dx/d*nd, selfY + dy/d*nd)` — the direction `dx/d, dy/d` is untouched, only the
distance changes. The fired bearing is `aimAngle(self, pred)` (`ModularBot.nim:1208`), so scaling the
aim distance cannot move the bearing. The knob is a **radial range correction**, not a lead
multiplier, and cannot express "less lead". Per the task rule, arms `rad075`/`rad050` were **skipped**
and the experiment ran as **2 arms × 15 runs**.

## HeadOn really does ignore `bulletSpeed`

`common_libs/guns/head_on.nim:9` returns `GunPrediction(x: state.enemyX, y: state.enemyY)`, never
reading its `bulletSpeed` argument. The rack calls it for the selected power bin and the fire block
takes the bearing straight to that point. So the premise holds: HeadOn applies **zero lead**,
independent of power. The `headon` arm's liveness check passed (its env reached the boot report in
15/15 runs), so this was HeadOn and only HeadOn.

## Primary result — damage/run and round wins [MEASURED]

| arm | runs | dmg/run | dmgtk/run | round wins | win% | shots/run | hits taken/run |
|---|---:|---:|---:|---:|---:|---:|---:|
| `control` (shipped Pattern-only) | 15 | **279** | 211 | **48/105** | 45.7 | 785 | 93 |
| `headon` (HeadOn-only) | 15 | **14** | 228 | **0/105** | 0.0 | 580 | 72 |

Per-run damage (`control`): 263 307 294 221 290 235 327 262 330 312 274 292 288 281 217.
Per-run damage (`headon`): 4 8 4 17 14 10 28 18 0 36 17 8 14 14 15.

| metric | diff (control−headon) | perm p | method | MDE (abs) | MDE vs control mean |
|---|---:|---:|---|---:|---:|
| dmg/run | **+265.7** | **<0.0001** | MC/B=1,000,000 (se 0.0000) | 35.8 | 12.8% of 279.5 |
| round wins | **+3.20** | **<0.0001** | MC/B=1,000,000 (se 0.0000) | 1.29 | 40.4% of 3.2 |

Mann-Whitney U cross-check p = 0.0000 on both. Round-level Fisher p < 0.0001 (anti-conservative).
The effect is ~7× the damage MDE; this is not an under-powered null.

## Hit rate by range band — the load-bearing breakdown [MEASURED]

Pooled over each arm's 15 runs; band = shooter→target distance at the fire tick (same bands as the
offline ruler). HeadOn loses the long-range bands by a landslide — the whole-battle defeat is **not**
a close-range artefact.

| band (px) | control shots / hits / rate | headon shots / hits / rate |
|---|---:|---:|
| 0–100 | 3 / 2 / 66.7% | 1 / 0 / 0.0% |
| 100–200 | 28 / 4 / 14.3% | 97 / 8 / 8.2% |
| 200–300 | 211 / 26 / 12.3% | 469 / 12 / 2.6% |
| **300–450** | **4590 / 565 / 12.3%** | **3701 / 21 / 0.6%** |
| **450+** | **6671 / 616 / 9.2%** | **4177 / 15 / 0.4%** |
| **ALL** | 11503 / 1213 / **10.5%** | 8445 / 56 / **0.7%** |

Per-band permutation test on per-run band rates (`arm − control`):

| band | diff (pp) | p | method | MDE (pp) |
|---|---:|---:|---|---:|
| 100–200 | +1.93 | 0.6609 | exact | 12.4 |
| 200–300 | −12.12 | <0.0001 | MC/B=200,000 | 12.1 |
| 300–450 | **−11.84** | **<0.0001** | MC/B=200,000 | 2.0 |
| 450+ | **−8.89** | **<0.0001** | MC/B=200,000 | 1.1 |
| ALL | −9.90 | <0.0001 | MC/B=200,000 | 1.0 |

The two long-range bands separate at **4–8× their MDE**, overwhelmingly in HeadOn's *favour* being
false. Note the 98%+ of shots that land at 300+ px, exactly as the offline ruler reported.

## Offline ruler vs live [MEASURED]

| source | metric | Pattern 300–450 | HeadOn 300–450 | Pattern 450+ | HeadOn 450+ |
|---|---|---:|---:|---:|---:|
| offline `prediction_quality_results.txt` | meanAbs err (deg) | 17.53 | **14.61** | 16.19 | **12.33** |
| offline | hitProxy | 0.104 | **0.105** | 0.077 | **0.098 (+27%)** |
| **live (this run)** | **hit rate** | **12.3%** | **0.6%** | **9.2%** | **0.4%** |

The ruler said HeadOn is equal-or-better at 300+; live it is 20×/23× worse. The ruler is a per-tick,
open-loop replay of a **fixed** enemy track: a no-lead gun's aim error is scored against the enemy's
true future position on that same pre-recorded dodge, which is not the distribution a *different*
bullet induces. Live, the bullet changes the dodge, and the static gun simply does not lead the
surfer. This is precisely the open-loop/live gap the ruler cannot see. **The offline aim-error ruler
is not a valid predictor of the live HeadOn-vs-Pattern question — do not use it to rank no-lead guns
at range.**

## Caveats and what is inferred

- **[MEASURED]** All numbers above, from this session's server-side events sidecar; one frozen
  binary; liveness OK for both arms; `wins == firstPlaces` 15/15 both arms.
- **[INFERRED]** The rack-membership change also removes a gun's 4 virtual bullets/tick from the
  shared order-sensitive ring (`docs/gun_rack_analysis.md` §1.1). Both arms are single-gun racks and
  the effect size (0/105 rounds, ~7× MDE) is far too large for ring-order to explain.
- **[MEASURED]** One adversary (the real DrussGT jar). The 70-run offline corpus this ruler was built
  on is the same live capture set, so the two disagree on the *same* adversary — the disagreement is
  the open-loop/live gap, not a matchup difference.
- **Reproduce:** `tools/ab/ab_run.sh --arms tools/ab/arms_headon.txt --runs 15 --outdir /tmp/ab_headon --conc 8 --rounds 7`;
  `python3 tools/ab/ab_analyze.py /tmp/ab_headon --reference control`;
  `python3 tools/ab/ab_range_bands.py /tmp/ab_headon --reference control`.