diff --git a/src/AcDream.App/Rendering/PortalVisibilityBuilder.cs b/src/AcDream.App/Rendering/PortalVisibilityBuilder.cs
index f828abfb..ebf70c94 100644
--- a/src/AcDream.App/Rendering/PortalVisibilityBuilder.cs
+++ b/src/AcDream.App/Rendering/PortalVisibilityBuilder.cs
@@ -200,6 +200,20 @@ public static class PortalVisibilityBuilder
 
                 bool dx = pvDump && cell.Portals[i].OtherCellId == 0xFFFF;
                 bool eyeInsideOpening = EyeInsidePortalOpening(poly, cell.WorldTransform, cameraPos);
+
+                // (R-A2b Phase 1 pin, throwaway) Log the side-test inputs for EVERY portal so a back-portal
+                // traversal (cell=0x..0173 p->0x0171) can be attributed to B1 (eyeInsideOpening bypasses the
+                // side-cull) vs B2 (CameraOnInteriorSide returns interior where retail's InitCell culls).
+                // |D|<=1.75 means eyeInsideOpening is in range. Strip with the rest of the [pv-trace] apparatus.
+                if (trace != null)
+                {
+                    bool camInterior = i >= cell.ClipPlanes.Count || CameraOnInteriorSide(cell, i, cameraPos);
+                    float sideD = (i < cell.ClipPlanes.Count && cell.ClipPlanes[i].Normal.LengthSquared() >= 1e-8f)
+                        ? Vector3.Dot(cell.ClipPlanes[i].Normal, Vector3.Transform(cameraPos, cell.InverseWorldTransform)) + cell.ClipPlanes[i].D
+                        : float.NaN;
+                    trace.Add($"sidechk cell=0x{cell.CellId:X8} p{i}->0x{portal.OtherCellId:X4} camInterior={camInterior} eyeIn={eyeInsideOpening} D={(float.IsNaN(sideD) ? "na" : sideD.ToString("F2"))}");
+                }
+
                 bool sideAllowed = true;
 
                 // Portal-side test: only traverse a portal the camera is on the interior side of