fix: COUCH gate — Kelvin wave regime check

The COUCH gate now has TWO stages (matching BraidStateN.lean):

Stage A — Rossby/Kelvin regime:
  - Rossby drift ≠ 0 → Rossby regime (dispersive, active mixing) → PASS
  - Rossby drift = 0 → Kelvin regime (boundary-trapped, NO mixing) → FAIL

  The Kelvin regime is the degenerate case: perfectly balanced chiral
  distribution. Energy dissipation rate is ZERO (proven in
  rossby_energy_dissipation_rate: requires isActive=true).

  kelvinLabels8 (all achiral_stable) → drift=0 → Kelvin → FAIL
  rossbyLabels8 (alternating left/right) → drift≠0 → Rossby → PASS

  This is the 'q=1 degenerate' / 'rational surface' / 'stuck' case.

Stage B — scarred contention:
  - scarred_count → self_loop → threshold (unchanged)

A config passes COUCH iff BOTH stages pass.

Updated both pipeline_core.py (Python) and chiral_cross_enrich.wgsl
(GPU shader) with the Kelvin check.

python/chiral_cross_enrich.wgsl

@@ -113,21 +113,30 @@ fn compute_helical(step: u32) -> u32 {
     return ((step * GOLDEN_ANGLE) / Q16_ONE) % EXOTIC_CLASSES;
 }
 
-/// COUCH stability: scarred count → self-loop → threshold check.
+/// COUCH stability: two-stage check.
+/// Stage A: Rossby/Kelvin regime (drift=0 → Kelvin → boundary-trapped → FAIL)
+/// Stage B: scarred contention (self-loop < threshold)
 fn compute_couch(config_id: u32) -> u32 {
+    // Stage A: Rossby drift must be non-zero (Kelvin regime fails)
+    let drift = compute_rossby(config_id);
+    if (drift == 0) {
+        // Kelvin regime: boundary-trapped, no mixing, zero dissipation
+        // (proven: rossby_energy_dissipation_rate requires isActive)
+        return 0u;  // COUCH FAILS — stuck like AVX-512 (self_loop=0.885)
+    }
+
+    // Stage B: scarred contention check
     var scarred_count: u32 = 0u;
     for (var s: u32 = 0u; s < N_STRANDS; s = s + 1u) {
         if (get_chiral_type(config_id, s) == 1u) {  // chiral_scarred
             scarred_count = scarred_count + 1u;
         }
     }
-    // self_loop = 57942 * scarred_count / 8 (Q16_16)
     let self_loop = (57942u * scarred_count) / N_STRANDS;
-    // COUCH stable if self_loop < threshold
     if (self_loop < COUCH_THRESHOLD) {
-        return 1u;  // stable
+        return 1u;  // COUCH PASSES — Rossby active + low contention
     }
-    return 0u;  // unstable
+    return 0u;  // COUCH FAILS — too much scarred contention
 }
 
 /// Main kernel: each thread processes one cross-enriched configuration.

scripts/pipeline_core.py

@@ -257,16 +257,28 @@ class MultisurfacePacker(Filter):
 # ── Stage 5: COUCH — Geometric stability via Rossby drift ─────────────
 
 class COUCHFilter(Filter):
-    """COUCH gate: Rossby drift determines stability.
+    """COUCH gate: two-stage stability check.
 
-    Uses the ACTUAL rossbyDriftFromChirality from BraidStateN.lean:
-      left=+65536, right=-65536, scarred=+32768, achiral=0
+    Stage A — Rossby/Kelvin regime check (from BraidStateN.lean):
+      - Rossby drift ≠ 0 → Rossby regime (dispersive, active mixing) → PASS
+      - Rossby drift = 0 → Kelvin regime (boundary-trapped, NO mixing) → FAIL
 
-    Non-zero drift → Rossby regime (active, dispersive) → COUCH passes
-    Zero drift → Kelvin regime (boundary-trapped) → COUCH may fail
+      The Kelvin regime is the degenerate case: perfectly balanced chiral
+      distribution (left+right cancel, no scarred). Energy dissipation rate
+      is ZERO (proven: rossby_energy_dissipation_rate requires isActive).
+      This is the "q=1 degenerate" / "rational surface" / "AVX-512 stuck"
+      case — the system can't mix.
 
-    Also computes helical_residue (winding number mod 28) from
-    HopfFibration.lean: ⌊k·ψ⌋ mod 28 where ψ=25042 (Q16_16).
+      rossbyLabels8 (BraidStateN.lean line 327): alternating left/right
+      → drift ≠ 0 → Rossby → dispersive → COUCH passes
+      kelvinLabels8 (BraidStateN.lean line 338): all achiral_stable
+      → drift = 0 → Kelvin → boundary-trapped → COUCH fails
+
+    Stage B — Scarred contention check (from HCMR):
+      - scarred_count → self_loop proxy → threshold check
+      - High scarred count = high contention = AVX-512 regime
+
+    A config passes COUCH iff BOTH stages pass.
     """
     def __init__(self, threshold=Q16_THRESHOLD_COUCH): self.threshold = threshold
     @property
@@ -274,17 +286,25 @@ class COUCHFilter(Filter):
     def apply(self, configs, ctx):
         result = []
         for c in configs:
-            # Rossby drift (actual implementation from BraidStateN.lean)
+            # Stage A: Rossby/Kelvin regime
             drift, is_active = rossby_drift(c.chiral)
             c.rossby_drift = drift
-            # Helical residue (winding number mod 28, from HopfFibration.lean)
+            if not is_active:
+                # Kelvin regime: boundary-trapped, no mixing → COUCH FAILS
+                c.metadata["regime"] = "kelvin"
+                c.self_loop = Q16_AVX_SELFLOOP  # stuck, like AVX-512
+                continue
+            c.metadata["regime"] = "rossby"
+
+            # Stage B: scarred contention
+            scarred_count = sum(1 for cl in c.chiral if cl == "chiral_scarred")
+            c.self_loop = (Q16_AVX_SELFLOOP * scarred_count) // max(len(c.chiral), 1)
+            if c.self_loop >= self.threshold:
+                continue  # too much contention
+
+            # Helical residue (winding mod 28, from HopfFibration.lean)
             step = c.metadata.get("step", 0)
             c.helical_residue = helical_residue(step)
-            # COUCH stable if Rossby active (non-zero drift) or scarred count low
-            scarred_count = sum(1 for cl in c.chiral if cl == "chiral_scarred")
-            # Self-loop proxy: scarred strands cause contention
-            c.self_loop = (Q16_AVX_SELFLOOP * scarred_count) // max(len(c.chiral), 1)
-            if c.self_loop < self.threshold:
             result.append(c)
         return result