diag(physics): L.2.3g — log step-up SUCCESS/FAIL + landing plane

Enhances the ACDREAM_DUMP_STEPUP=1 diagnostic so we can characterize
the steep-roof bug. The original log only showed the input collision
normal of the polygon that triggered step-up; it didn't show what
polygon the step-up actually LANDED on (which can differ — step-up
scans for any walkable polygon within StepUpHeight reach, so it might
ascend onto a flatter surface higher up than the polygon hit).

New log lines:
  stepup: enter normal=(...) → WALKABLE/STEEP, OnWalkable=..., StepUpHeight=...
  stepup: SUCCESS — landed on plane normal=(...) → WALKABLE/STEEP, new CheckPos=...
  stepup: FAILED — sliding back along normal

When user climbs the offending steep roof, the SUCCESS line will tell
us whether the landing polygon is steeper than FloorZ=0.66 (then we
have a threshold bug) or whether step-up scanned past the steep slope
to land on a flatter polygon (then the StepUpHeight reach is too
permissive).

Also logs CurPos and final CheckPos so we can correlate to in-world
location.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Physics/TransitionTypes.cs

@@ -1389,21 +1389,23 @@ public sealed class Transition
         var ci = CollisionInfo;
         var oi = ObjectInfo;
 
-        // L.2.3f (2026-04-29): diagnostic for steep-roof bug. Log the
+        // L.2.3f (2026-04-29): diagnostic for steep-roof bug. Logs the
-        // collision normal Z so we can confirm whether the polygon being
+        // input polygon normal that triggered step-up. The verdict tells
-        // stepped up onto is "walkable" (normal.Z >= FloorZ ≈ 0.66) or
+        // whether THIS polygon would pass FloorZ (≈ 0.66) — but actual
-        // not (≈ 0.087 LandingZ when not OnWalkable). If we see steep
+        // step-up acceptance depends on the polygon found by step_sphere_down
-        // normals being accepted, the issue is in the find_walkable
+        // INSIDE the recursive TransitionalInsert, which may be different.
-        // threshold rather than the StepUpHeight reach.
+        // The post-step "result=" line below logs that outcome.
-        if (Environment.GetEnvironmentVariable("ACDREAM_DUMP_STEPUP") == "1")
+        bool diag = Environment.GetEnvironmentVariable("ACDREAM_DUMP_STEPUP") == "1";
+        if (diag)
         {
             float floor = PhysicsGlobals.FloorZ;
             string verdict = collisionNormal.Z >= floor ? "WALKABLE" : "STEEP";
             Console.WriteLine(
-                $"stepup: normal=({collisionNormal.X:F3},{collisionNormal.Y:F3},{collisionNormal.Z:F3}) " +
+                $"stepup: enter normal=({collisionNormal.X:F3},{collisionNormal.Y:F3},{collisionNormal.Z:F3}) " +
                 $"|Z|={collisionNormal.Z:F3} vs FloorZ={floor:F3} → {verdict}, " +
                 $"OnWalkable={oi.State.HasFlag(ObjectInfoState.OnWalkable)}, " +
-                $"StepUpHeight={oi.StepUpHeight:F3}");
+                $"StepUpHeight={oi.StepUpHeight:F3}, " +
+                $"CurPos=({sp.CurPos.X:F2},{sp.CurPos.Y:F2},{sp.CurPos.Z:F2})");
         }
 
         // L.2.3c (2026-04-29): capture the existing contact plane BEFORE
@@ -1443,6 +1445,28 @@ public sealed class Transition
         sp.StepUp    = false;
         sp.WalkableValid = false;
 
+        // L.2.3f: log the result + landing plane if step-up succeeded.
+        // This is the actual surface the player ended up on, which may
+        // differ from the input collision normal (e.g. step-up scanned
+        // past a steep slope and landed on a flatter polygon higher up).
+        if (diag)
+        {
+            if (stepDown && ci.ContactPlaneValid)
+            {
+                float floor = PhysicsGlobals.FloorZ;
+                string verdict = ci.ContactPlane.Normal.Z >= floor ? "WALKABLE" : "STEEP";
+                Console.WriteLine(
+                    $"stepup: SUCCESS — landed on plane normal=" +
+                    $"({ci.ContactPlane.Normal.X:F3},{ci.ContactPlane.Normal.Y:F3},{ci.ContactPlane.Normal.Z:F3}) " +
+                    $"|Z|={ci.ContactPlane.Normal.Z:F3} vs FloorZ={floor:F3} → {verdict}, " +
+                    $"new CheckPos=({sp.CheckPos.X:F2},{sp.CheckPos.Y:F2},{sp.CheckPos.Z:F2})");
+            }
+            else
+            {
+                Console.WriteLine($"stepup: FAILED — sliding back along normal");
+            }
+        }
+
         if (!stepDown)
         {
             sp.RestoreCheckPos();