New harness (common_libs/gun_harness/prediction_quality.nim +
common_libs/tests/run_prediction_quality.nim): per-gun single-tick aim error in
degrees against the true continuous interception point on the recorded
live-vs-real-DrussGT corpus (/tmp/tfil_ab2/out, 70 runs, 899607 ticks), per
range band, with the hit-probability proxy mean(|err|<=atan(18/range)).
Validated: recorded hits separate from misses 13.34x px (reference 11.59x),
perfect-oracle max |err| = 0, correct ordering on synthetic ground truth, two
full runs byte-identical. Fixed a wrap180 bug (Nim float mod keeps the dividend
sign) that inflated the negative error tail.
Bar (mean|err| deg [hitProxy] at 450+): Pattern 16.19 [0.077], naive-linear
22.86 [0.054], TMHorizon 16.20 [0.076], BitBrain 16.20 [0.077], static HeadOn
12.33 [0.098], oracle 0 [1.0]. Lead-gain sweep on Pattern is a dead end (1.0
wins every band). Naive-linear applies ~1.8x Pattern's lead but carries no more
lead information (corr 0.178 vs 0.165) and is strictly worse. Ledger:
docs/bitbrain_campaign.md. All verdicts remain live-only.
