routeV: margin (p75 clean / p75 hack) routing band, route the confident tail

Was the widest band (min clean, max hack): routed even neutral rollouts
(~0.4 of a cos=0 gradient), the over-route that costs solve. Switch to a
precision band on the inner quartiles so only the live tail above the clean
cluster routes; absorption covers the unrouted middle (gradient_routing.md
L420; SGTM tolerates ~40% undiscovered, Fig5b). p75 not min/max: 10 pairs
make the extremes single-sample noisy. Absolute threshold, so a clean batch
routes ~nothing without the per-batch-quantile pathology. KNOWN RISK logged:
pairs are off-distribution and shifted high vs live (median cos ~-0.06), so
the band may under-route; watch rout, fall back is a live-cos quantile gate.

Co-Authored-By: Claudypoo <288921227+claudypoo@users.noreply.github.com>

src/vgrout/train.py

@@ -339,17 +339,38 @@ def _zone_stats(f: torch.Tensor, w: torch.Tensor) -> tuple[float, ...]:
 
 
 def route_band_edges(raw_grads: dict, v_grad: dict, device) -> dict[str, tuple[float, float]]:
-    """Per-module routing band (lower, upper) from the contrastive pairs ALONE -- the
-    pair-calibrated replacement for the old live-detector τ. lower = MIN clean-pair cosine
-    to v_grad; upper = MAX hack-pair cosine. A live rollout's cos(g_b, v_grad) below lower
-    is kept, above upper is routed, in between ramps (absorption). min/max (not mean) is the
-    conservative "degrade to absorb" edge: almost nothing sits below the smallest clean
-    cosine, so when uncertain the rollout absorbs into the quarantine rather than escaping
-    into the deployed knob. raw_grads carries the train-pair per-pair δS grads as
-    `hack/{name}` / `clean/{name}` [n_pairs, r]. Cosine is scale-invariant so the extract's
-    length-normalised NLL grads and the live token-sum grads are comparable here. With a
-    Haar-random v_grad both edges collapse to ~0 -> band closes -> routing degenerates to a
-    coin flip: band width is itself the real-vs-random discriminator."""
+    """Per-module routing MARGIN band (lower, upper) from the contrastive pairs ALONE -- the
+    pair-calibrated replacement for the old live-detector τ. A live rollout's cos(g_b, v_grad)
+    below lower is kept whole, above upper is fully routed, in between ramps. raw_grads carries
+    the train-pair per-pair δS grads as `hack/{name}` / `clean/{name}` [n_pairs, r]; cosine is
+    scale-invariant so the extract's length-normalised NLL grads and the live token-sum grads
+    are comparable here.
+
+    Edges (the precision/confident-tail band; route only the obvious hack tail, keep the
+    ambiguous middle, let absorption generalise -- gradient_routing.md L420, SGTM tolerates
+    ~40% undiscovered with leak<0.02, Fig 5b). Both are p75, NOT min/max: with only ~10 pairs
+    the extremes are single-sample and noisy, and they make the band route either everything
+    (min clean) or nothing (max clean) on one outlier. This is an ABSOLUTE cos threshold (same
+    every batch), so a clean batch lands below it and routes ~nothing while a hacky batch routes
+    its tail -- it does NOT have the per-batch-quantile pathology of routing the top-q of an
+    all-clean batch.
+      lower = p75 clean-pair cosine. Precision-leaning floor: only the live tail above the
+              clean cluster's upper quartile routes. Routing clean is the expensive error
+              (gradient_routing.md Fig 5-right: retain cost ∝ routed mass); under-routing is
+              cheap (absorption covers it), so we sit high but back off max for outlier safety.
+      upper = p75 hack-pair cosine. Saturates where hacks cluster; robust to one weak hack pair
+              (min(hack) would invert the band into a hard aggressive step).
+    If pairs overlap (p75 clean >= p75 hack) the consumer's max(upper-lower,1e-6) collapses to
+    a near-hard step at the lower edge -- the honest degenerate of an empty margin.
+
+    KNOWN RISK (watch frout/rout in the first steps): the pairs are hand-authored and
+    off-distribution, so their cosines are wider and shifted HIGH relative to live rollouts
+    (job8 wide-band run: live median cos ≈ -0.06, below the pair-hack cluster). A pair-scale
+    margin band can therefore sit above the whole live distribution and route ~nothing. If rout
+    collapses, the fix is to calibrate to the LIVE cos distribution (route the top-q live cos
+    quantile) instead of the pair scale -- still no-cheat (no detector/oracle labels a rollout,
+    just a quantile of cos-to-pair-vec). With a Haar-random v_grad the band closes (real-vs-
+    random discriminator)."""
     band = {}
     for name in v_grad:
         v = v_grad[name].detach().cpu().float()
@@ -357,7 +378,7 @@ def route_band_edges(raw_grads: dict, v_grad: dict, device) -> dict[str, tuple[f
         gc = raw_grads[f"clean/{name}"].float()
         ch = (gh @ v) / gh.norm(dim=1).clamp_min(1e-12)             # [n_pairs] hack-pair cosines
         cc = (gc @ v) / gc.norm(dim=1).clamp_min(1e-12)             # [n_pairs] clean-pair cosines
-        band[name] = (cc.min().item(), ch.max().item())            # (lower, upper)
+        band[name] = (cc.quantile(0.75).item(), ch.quantile(0.75).item())   # (lower=p75 clean, upper=p75 hack)
     return band
 
 
@@ -489,10 +510,12 @@ def main(cfg: Config) -> int:
             _mean_lo = sum(lo for lo, _ in route_band.values()) / len(route_band)
             _mean_hi = sum(hi for _, hi in route_band.values()) / len(route_band)
             _mean_bw = _mean_hi - _mean_lo
-            logger.info(f"routeV band: edges from {len(route_band)} modules, "
-                        f"mean lower(min clean cos)={_mean_lo:+.3f}, mean upper(max hack cos)={_mean_hi:+.3f}, "
-                        f"mean width={_mean_bw:+.3f} (>0 = pairs separate; ~0 = random/degenerate). "
-                        f"Live cos below lower -> kept; above upper -> routed; between -> ramps (frout).")
+            logger.info(f"routeV MARGIN band: edges from {len(route_band)} modules, "
+                        f"mean lower(p75 clean cos)={_mean_lo:+.3f}, mean upper(p75 hack cos)={_mean_hi:+.3f}, "
+                        f"mean width={_mean_bw:+.3f} (>0 = pairs separate; <0 = overlap -> hard step at max clean). "
+                        f"Live cos below lower -> kept; above upper -> routed; between -> ramps (rout/frout). "
+                        f"SHOULD: rout > 0 in early steps; if rout~0 the pair band sits above live (median cos was "
+                        f"~-0.06 on the wide run) -> switch to a live-cos quantile gate.")
             # On a REAL v_grad the band must open (hack pairs align more than clean).
             # A collapsed/inverted real band = broken extraction silently mimicking the
             # random control -> fail loud. The Haar control is allowed to collapse.