Implement NUL operator canonical ΔNFR densification dynamics

Co-authored-by: fermga <203334638+fermga@users.noreply.github.com>

Author: Copilot

src/tnfr/config/defaults_core.py

@@ -95,6 +95,11 @@ class CoreDefaults:
             # This preserves structural identity at boundary (EPI_MAX as identity frontier).
             "VAL_scale": 1.05,
             "NUL_scale": 0.85,
+            # NUL canonical ΔNFR densification factor: implements structural pressure
+            # concentration due to volume reduction. When V' = V × 0.85, density increases
+            # by ~1.176× geometrically. Canonical value 1.35 accounts for nonlinear
+            # structural effects at smaller scales, per TNFR theory.
+            "NUL_densification_factor": 1.35,
             "THOL_accel": 0.10,
             "ZHIR_theta_shift": 1.57079632679,
             "NAV_jitter": 0.05,

src/tnfr/operators/__init__.py

@@ -1223,6 +1223,37 @@ def _op(node: NodeProtocol, gf: GlyphFactors) -> None:
         # Always scale νf (existing behavior)
         _op_scale(node, factor)
 
+        # NUL canonical ΔNFR densification (implements structural pressure concentration)
+        if glyph is Glyph.NUL:
+            # Volume reduction: V' = V · scale_factor (where scale_factor < 1.0)
+            # Density increase: ρ_ΔNFR = ΔNFR / V' = ΔNFR / (V · scale_factor)
+            # Result: ΔNFR' = ΔNFR · densification_factor
+            #
+            # Physics: When volume contracts by factor λ < 1, structural pressure
+            # concentrates by factor 1/λ > 1. For NUL_scale = 0.85, densification ≈ 1.176
+            #
+            # Default densification_factor from config (typically 1.3-1.5) provides
+            # additional canonical amplification beyond geometric 1/λ to account for
+            # nonlinear structural effects at smaller scales.
+            densification_key = "NUL_densification_factor"
+            densification_default = 1.35  # Canonical default: moderate amplification
+            densification_factor = get_factor(gf, densification_key, densification_default)
+            
+            # Apply densification to ΔNFR (use lowercase dnfr for NodeProtocol)
+            current_dnfr = node.dnfr
+            node.dnfr = current_dnfr * densification_factor
+            
+            # Record densification telemetry for traceability
+            telemetry = node.graph.setdefault("nul_densification_log", [])
+            telemetry.append(
+                {
+                    "dnfr_before": current_dnfr,
+                    "dnfr_after": float(node.dnfr),
+                    "densification_factor": densification_factor,
+                    "contraction_scale": factor,
+                }
+            )
+
         # Edge-aware EPI scaling (new behavior) if enabled
         edge_aware_enabled = bool(
             node.graph.get(

src/tnfr/operators/metrics.py

@@ -1292,7 +1292,7 @@ def expansion_metrics(
 def contraction_metrics(
     G: TNFRGraph, node: NodeId, vf_before: float, epi_before: float
 ) -> dict[str, Any]:
-    """NUL - Contraction metrics: νf decrease, core concentration.
+    """NUL - Contraction metrics: νf decrease, core concentration, ΔNFR densification.
 
     Parameters
     ----------
@@ -1308,22 +1308,43 @@ def contraction_metrics(
     Returns
     -------
     dict
-        Contraction-specific metrics including structural compression
+        Contraction-specific metrics including structural compression and
+        canonical ΔNFR densification tracking.
     """
     vf_after = _get_node_attr(G, node, ALIAS_VF)
     epi_after = _get_node_attr(G, node, ALIAS_EPI)
-    dnfr = _get_node_attr(G, node, ALIAS_DNFR)
+    dnfr_after = _get_node_attr(G, node, ALIAS_DNFR)
 
-    return {
+    # Extract densification telemetry if available
+    densification_log = G.graph.get("nul_densification_log", [])
+    densification_factor = None
+    dnfr_before = None
+    if densification_log:
+        # Get the most recent densification entry for this node
+        last_entry = densification_log[-1]
+        densification_factor = last_entry.get("densification_factor")
+        dnfr_before = last_entry.get("dnfr_before")
+
+    metrics = {
         "operator": "Contraction",
         "glyph": "NUL",
         "vf_decrease": vf_before - vf_after,
         "vf_final": vf_after,
         "delta_epi": epi_after - epi_before,
         "epi_final": epi_after,
-        "dnfr_final": dnfr,
+        "dnfr_final": dnfr_after,
         "contraction_factor": vf_after / vf_before if vf_before > 0 else 1.0,
     }
+    
+    # Add densification metrics if available
+    if densification_factor is not None:
+        metrics["densification_factor"] = densification_factor
+        metrics["dnfr_densified"] = True
+    if dnfr_before is not None:
+        metrics["dnfr_before"] = dnfr_before
+        metrics["dnfr_increase"] = dnfr_after - dnfr_before if dnfr_before else 0.0
+    
+    return metrics
 
 
 def self_organization_metrics(