fix #137 (corridor phantom resolved): slide_sphere opposing branch returns Collided; the 'wall' was synthetic

The mechanism-1 theory (PortalSide portal polys solid in our physics set)
is REFUTED for the corridor repro, and the remaining half of the phantom
is fixed — no cdb session needed:

- The live hit normal (-1.00,0.03,-0.03) matches NO dat polygon: a
  world-space sweep of both seam cells + every portal-adjacent neighbor
  (CorridorSeam_FindPolygonMatchingLiveHit) returns zero candidates. The
  normal is the negated movement direction — the SYNTHETIC value
  slide_sphere's opposing-normals branch records (reversed = -gDelta).
- Cell 0x8A02016E has IDENTITY rotation (the prior session's 'rotation
  maps the portal planes into the -X wall' was a misattribution). The
  PortalSide polys to 0x011E are +-Y planes 1.4 m beside the player's
  track, perpendicular to the +X run — pos_hits_sphere's directional
  cull rejects them for that movement. They ARE referenced by the dat's
  physics-BSP leaves (CorridorCell_PhysicsBspLeafMembership), so retail
  tests them too when approached into their plane; the dat's
  keep-PortalSide / strip-ExactMatch asymmetry reads as intentional
  (solid window/grate-class portals). No portal-poly filter — exactly
  the blanket-skip the pickup warned against.
- Port fix: CSphere::slide_sphere's opposing-normals branch
  (0x005375d7-0x0053762c) records the reversed displacement and returns
  COLLIDED_TS; our port returned OK ('retail returns OK here' was a
  decomp misread), letting the step complete as-is with the synthetic
  collision normal that validate's epilogue then persisted as the
  sliding normal the wedge absorbed on. TransitionTypes opposing branch
  now returns Collided; pinned by
  SlideSphere_OpposingNormals_ReturnsCollided_WithReversedDisplacementNormal
  (RED->GREEN).
- Dat-backed replay (Issue137CorridorSeamReplayTests) reproduces the
  live hit frame verbatim (same in/out to the millimeter, same 016E->017A
  transit, same +8mm settle) and runs the corridor CLEAN: hit=no, no
  sliding normal persisted, six further forward frames advance freely.
- Inspection tests extended: physics-BSP leaf membership walk +
  hit-normal candidate sweep + downward-poly sweep (all report-style,
  dat-gated). Pickup prompt banner'd SUPERSEDED; ISSUES #137 updated
  (door half stays open); audit doc extended with the resolution.

Suites: Core 2551 / App 713 / UI 425 / Net 385, 0 failures.

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

src/AcDream.Core/Physics/TransitionTypes.cs

@@ -3730,15 +3730,25 @@ public sealed class Transition
             return TransitionState.Slid;
         }
 
-        // Opposing normals: give up, reverse direction.
-        // Retail returns OK here to allow retry with the reversed normal.
+        // Opposing normals (collision normal anti-parallel to the contact
+        // plane, e.g. a ceiling-facing normal while grounded): record the
+        // REVERSED displacement as the collision normal and return COLLIDED.
+        // Retail CSphere::slide_sphere 0x00537440 @0x005375d7-0x0053762c:
+        // `*normal = -gDelta; normalize_check_small; set_collision_normal;
+        // return 2 (COLLIDED_TS)`. #137 (2026-07-06): this previously
+        // returned OK ("to allow retry with the reversed normal" — a decomp
+        // misread), which let the step complete as-is carrying a SYNTHETIC
+        // reversed-movement collision normal — the live corridor hit's
+        // `n=(-1.00,0.03,-0.03)` (= the negated run direction) matched no
+        // dat polygon; validate's epilogue then turned it into a persisted
+        // sliding normal and wedged all forward motion.
         Vector3 reversed = -gDelta;
         if (reversed.LengthSquared() > PhysicsGlobals.EpsilonSq)
         {
             reversed = Vector3.Normalize(reversed);
             ci.SetCollisionNormal(reversed);
         }
-        return TransitionState.OK;
+        return TransitionState.Collided;
     }
 
     // -----------------------------------------------------------------------