VIOLET V3d: base-sizer parity harness + gate vs recorded BLUE

parity_harness.py: median-curve parity of V3a VioletBetSizer vs recorded
dolphin.trade_events (vel_div->leverage), restricted to short-signal domain.
GATE PASSES on prod host: pearson 0.9998, max_abs_err 0.238 (budget 1.0) over
23 bins -> base conviction sizer reproduces BLUE's central tendency. Per-trade
scatter is the deferred SC/ACB/OB/gold modulation layer (separate finding doc).
3 unit + 1 gate green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

prod/clean_arch/violet/test_violet_parity.py

@@ -0,0 +1,80 @@
+"""V3d: base-sizer median-curve parity vs recorded BLUE (unit + @gate)."""
+
+from __future__ import annotations
+
+import json
+import sys
+from datetime import datetime, timezone
+from pathlib import Path
+
+sys.path.insert(0, "/mnt/dolphinng5_predict")
+
+import pytest
+
+from prod.clean_arch.violet.parity_harness import (
+    ParityReport, base_curve_parity, live_blue_sizer, load_recorded_samples_from_ch,
+)
+
+REPORTS_DIR = Path("/mnt/dolphinng5_predict/prod/VIOLET_dev/reports")
+
+
+def _base_samples(per_bin: int = 12):
+    """Synthetic samples drawn exactly from the base curve (perfect parity)."""
+    s = live_blue_sizer()
+    out = []
+    for k in range(2, 13):                     # vd = -0.02 .. -0.12, all on 0.01 bin centers
+        vd = -k / 100.0
+        base = s.calculate(capital=1.0, vel_div=vd, trade_direction=-1).conviction_leverage
+        out.extend([(vd, base)] * per_bin)
+    return out
+
+
+def test_perfect_base_samples_pass():
+    rep = base_curve_parity(_base_samples(), live_blue_sizer())
+    assert rep.passed
+    assert rep.max_abs_err == pytest.approx(0.0, abs=1e-6)
+    assert rep.pearson_r == pytest.approx(1.0, abs=1e-6)
+
+
+def test_median_tracks_base_under_minority_haircuts():
+    # majority at base, minority haircut down -> median still tracks base -> passes.
+    s = live_blue_sizer()
+    samples = []
+    for k in range(2, 13):                               # vd on 0.01 bin centers
+        vd = -k / 100.0
+        base = s.calculate(capital=1.0, vel_div=vd, trade_direction=-1).conviction_leverage
+        samples.extend([(vd, base)] * 8)                 # 8 at base
+        samples.extend([(vd, base * 0.3)] * 3)           # 3 haircut (minority)
+    rep = base_curve_parity(samples, s)
+    assert rep.passed
+
+
+def test_decorrelated_noise_fails_gate():
+    # leverage independent of vel_div -> low correlation -> gate fails (guard works).
+    import random
+    rng = random.Random(7)
+    samples = [(vd / 1000.0, rng.uniform(0.5, 9.0))
+               for vd in range(-60, -1) for _ in range(12)]
+    rep = base_curve_parity(samples, live_blue_sizer())
+    assert not rep.passed
+
+
+@pytest.mark.gate
+def test_base_curve_parity_vs_recorded_blue():
+    """GATE (prod host): the V3a base sizer reproduces BLUE's recorded median curve."""
+    samples = load_recorded_samples_from_ch(limit=5000)
+    assert len(samples) >= 500, f"too few recorded samples: {len(samples)}"
+    rep = base_curve_parity(samples, live_blue_sizer())
+
+    REPORTS_DIR.mkdir(parents=True, exist_ok=True)
+    ts = datetime.now(timezone.utc).strftime("%Y%m%d_%H%M%S")
+    (REPORTS_DIR / f"violet_v3_parity_{ts}.json").write_text(
+        json.dumps(rep.model_dump(), indent=2, default=str))
+
+    assert isinstance(rep, ParityReport)
+    assert rep.n_bins >= 5
+    assert rep.passed, (
+        f"base-curve parity FAILED: max_abs_err={rep.max_abs_err:.3f} "
+        f"(budget {rep.max_abs_err_budget}), pearson={rep.pearson_r:.3f} "
+        f"(budget {rep.pearson_budget})"
+    )