fix #172: port the retail CCylSphere collision family (platform step-up)

The Holtburg town-network portal platform (stab 0xC0A9B465, Setup
0x020019E3, CylSphere r=2.597m h=0.256m) blocked the player with an
endless rim slide instead of retail's step-up-onto-top — gating the
whole #137 dungeon repro. Surfaced when #149 started registering
BSP-less stab CylSpheres: the collision SHAPE became right while the
RESPONSE was still the hand-rolled AP-6 approximation (step-up gate +
radial wall-slide only).

Root cause: no cylinder-TOP support anywhere. DoStepUp's internal
step-down probe needs retail's step_sphere_down (0x0053a9b0) to land on
the flat top — a cylinder has no polygons for the walkable search — so
every step-up onto a wide cylinder failed into StepUpSlide and the
player orbited the rim (probe-confirmed: [cyl-test] result=Slid with
horizontal rim normals, launch-137-repro.log).

Port the full family verbatim: dispatcher intersects_sphere 0x0053b440
(placement/ethereal detection, step-down cap landing, walkable probe,
grounded step_sphere_up 0x0053b310, PathClipped collide_with_point
0x0053acb0, airborne land_on_cylinder 0x0053b3d0, Collide-flag
exact-TOI cap rest) + collides_with_sphere 0x0053a880 +
normal_of_collision 0x0053ab50 + slide_sphere 0x0053b2a0. Pseudocode +
settled BN x87 ambiguities (via ACE cross-ref) + two ACE bugs found and
NOT copied (head-slide foot-disp; see doc §8):
docs/research/2026-07-05-ccylsphere-collision-family-pseudocode.md

Ethereal cylinders now flow through retail's Layer-2 override
(pc:276961) instead of the early-OK consume — same net #150 behavior,
plus retail placement-blocked-by-cylinder semantics. SlideSphere gains
a sphereNum param (retail slides the head sphere by its own
displacement, 0x0053b843).

Register: AP-6 retired; AP-83 added (PerfectClip TOI tail decoded per
ACE, dead code until missiles). Tests: CylSphereFamilyTests (grounded
step-up onto the exact platform shape, tall-cylinder block, airborne
top landing, ethereal guard); the #42 self-shadow control assertion
updated to the retail observable (denied movement — the old ~1m radial
self-push was the approximation's artifact, not retail). Suites: Core
2533 / App 713 / UI 425 / Net 385 green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.Core.Tests/Physics/PhysicsEngineTests.cs

@@ -487,9 +487,20 @@ public class PhysicsEngineTests
             collisionType: ShadowCollisionType.Cylinder,
             cylHeight:     1.835f);
 
-        // Without the gate (movingEntityId == 0): the sweep must self-push.
-        // This proves the registry actually causes a collision, so the
-        // following filtered case is not a vacuous pass.
+        // Without the gate (movingEntityId == 0): the sweep must be
+        // INTERFERED WITH by the self-entry. This proves the registry
+        // actually causes a collision, so the following filtered case is not
+        // a vacuous pass.
+        //
+        // Observable updated for the 2026-07-05 CCylSphere family port: the
+        // old hand-rolled response radial-pushed the sphere ~1 m sideways
+        // (the original #42 symptom this test asserted). Retail's dispatcher
+        // (0x0053b440) resolves this geometry — airborne, dead-center on the
+        // cylinder axis, moving up — through land_on_cylinder → the Collide
+        // re-test, whose interp gate hard-stops (COLLIDED); ValidateTransition
+        // then reverts to a stay-put (no sideways teleport, Ok=true). The
+        // response-model-independent interference signal is the DENIED +Z
+        // movement: the sweep must NOT reach the +0.022 target.
         var unfiltered = engine.ResolveWithTransition(
             currentPos: bodyPos, targetPos: targetPos,
             cellId: 0xA9B40039u,
@@ -498,11 +509,11 @@ public class PhysicsEngineTests
             isOnGround: false,
             movingEntityId: 0u);
 
-        float unfilteredXY = MathF.Sqrt(
-            (unfiltered.Position.X - targetPos.X) * (unfiltered.Position.X - targetPos.X) +
-            (unfiltered.Position.Y - targetPos.Y) * (unfiltered.Position.Y - targetPos.Y));
-        Assert.True(unfilteredXY > 0.5f,
-            $"Without movingEntityId, sweep should self-push (got XY drift {unfilteredXY:F3}m)");
+        Assert.True(unfiltered.Position.Z < targetPos.Z - 0.01f,
+            $"Without movingEntityId, the sweep must collide with the mover's own " +
+            $"ShadowEntry and deny the +Z movement (retail: land_on_cylinder → " +
+            $"Collide re-test → COLLIDED → stay-put). Got Z={unfiltered.Position.Z:F4}, " +
+            $"target Z={targetPos.Z:F4}");
 
         // With the gate: the sweep must leave XY unchanged.
         var filtered = engine.ResolveWithTransition(