diff --git a/src/AcDream.Core/Physics/BSPQuery.cs b/src/AcDream.Core/Physics/BSPQuery.cs
index 6c7178b..289ff0e 100644
--- a/src/AcDream.Core/Physics/BSPQuery.cs
+++ b/src/AcDream.Core/Physics/BSPQuery.cs
@@ -1544,6 +1544,16 @@ public static class BSPQuery
 
             if (hit0 || hitPoly0 is not null)
             {
+                // L.2d slice 1.5 (2026-05-13): record the hit poly EARLY,
+                // before the StepSphereUp branch can recurse into
+                // ResolveWithTransition → FindObjCollisions and clobber the
+                // side-channel via the inner call's per-resolve clear. Path 5
+                // is the dominant grounded-player path; without this the
+                // probe's [resolve-bldg] line for every grounded BSP hit was
+                // mis-labeled as "n/a (cylinder)".
+                if (PhysicsDiagnostics.ProbeBuildingEnabled)
+                    PhysicsDiagnostics.LastBspHitPoly = hitPoly0;
+
                 var worldNormal = L2W(hitPoly0!.Plane.Normal);
                 // L.2.3b (2026-04-29): recursion guard. Retail
                 // (acclient_2013_pseudo_c.txt:272954) gates step_sphere_up on
@@ -1559,9 +1569,6 @@ public static class BSPQuery
                 // back to wall-slide so the inner sphere doesn't recurse.
                 collisions.SetCollisionNormal(worldNormal);
                 collisions.SetSlidingNormal(worldNormal);
-                // L.2d slice 1 (2026-05-13): diagnostic side-channel.
-                if (PhysicsDiagnostics.ProbeBuildingEnabled)
-                    PhysicsDiagnostics.LastBspHitPoly = hitPoly0;
                 return TransitionState.Slid;
             }
 
@@ -1575,6 +1582,12 @@ public static class BSPQuery
 
                 if (hit1 || hitPoly1 is not null)
                 {
+                    // L.2d slice 1.5 (2026-05-13): same early-record as foot
+                    // sphere — head-sphere wall hits also recurse via
+                    // StepSphereUp on the grounded path.
+                    if (PhysicsDiagnostics.ProbeBuildingEnabled)
+                        PhysicsDiagnostics.LastBspHitPoly = hitPoly1;
+
                     var worldNormal = L2W(hitPoly1!.Plane.Normal);
                     // L.2.3b: same recursion guard as the foot-sphere branch.
                     if (engine is not null && !path.StepUp && !path.StepDown)
@@ -1582,9 +1595,6 @@ public static class BSPQuery
 
                     collisions.SetCollisionNormal(worldNormal);
                     collisions.SetSlidingNormal(worldNormal);
-                    // L.2d slice 1 (2026-05-13): diagnostic side-channel.
-                    if (PhysicsDiagnostics.ProbeBuildingEnabled)
-                        PhysicsDiagnostics.LastBspHitPoly = hitPoly1;
                     return TransitionState.Slid;
                 }
             }
diff --git a/src/AcDream.Core/Physics/TransitionTypes.cs b/src/AcDream.Core/Physics/TransitionTypes.cs
index c881d2c..d5077b8 100644
--- a/src/AcDream.Core/Physics/TransitionTypes.cs
+++ b/src/AcDream.Core/Physics/TransitionTypes.cs
@@ -1469,12 +1469,14 @@ public sealed class Transition
             // the [resolve] probe surfaces the responsible entity id.
             bool collisionWasValidPre = ci.CollisionNormalValid;
 
-            // L.2d slice 1 (2026-05-13): clear the BSP-hit side-channel so the
-            // [resolve-bldg] emission below reads only this iteration's poly.
-            // Cylinder collisions leave it null on purpose (probe emits
-            // "hitPoly: n/a (cylinder)").
-            if (PhysicsDiagnostics.ProbeBuildingEnabled)
-                PhysicsDiagnostics.LastBspHitPoly = null;
+            // L.2d slice 1.5 (2026-05-13): no per-iteration LastBspHitPoly
+            // clear. BSPQuery writes the side-channel early (inside
+            // `if (hit0 || hitPoly0 != null)` BEFORE any StepSphereUp call),
+            // so by the time we read it back for the [resolve-bldg] emission
+            // it reflects THIS entity's hit (or stays null if BSP didn't
+            // hit). For cylinder dispatch we key the "n/a (cylinder)" label
+            // off `obj.CollisionType` directly at the emission site, so a
+            // stale BSP value from a prior iteration can't leak through.
 
             TransitionState result;
 
@@ -1588,10 +1590,19 @@ public sealed class Transition
                     $"               entOrigin_lb=({entOriginLb.X:F1},{entOriginLb.Y:F1},{entOriginLb.Z:F1})"));
 
                 var poly = PhysicsDiagnostics.LastBspHitPoly;
-                if (poly is null)
+                // L.2d slice 1.5 (2026-05-13): key the n/a label on the
+                // entity's CollisionType, not on LastBspHitPoly nullness —
+                // a BSP hit with null side-channel indicates a BSPQuery code
+                // path that didn't write (a bug; we should fix it, not
+                // pretend the entity was a cylinder).
+                if (obj.CollisionType == ShadowCollisionType.Cylinder)
                 {
                     sb.Append("\n               hitPoly: n/a (cylinder)");
                 }
+                else if (poly is null)
+                {
+                    sb.Append("\n               hitPoly: n/a (BSP path — side-channel not written, missing BSPQuery wire site)");
+                }
                 else
                 {
                     sb.Append(System.FormattableString.Invariant(