feat(phys): A6.P4 slice 1 — portal-reachable cellSet includes outdoor cells

Closes #99 (run-through doors regression from b3ce505).

The b3ce505 stopgap for #98 gates the outdoor 24m radial sweep on indoor
primary cells. Combined with ShadowObjectRegistry.GetNearbyObjects'
"skip outdoor ids" filter on the cellScope-pass loop, this meant doors
registered at outdoor cells (default cellScope=0u for server-spawned
entities at GameWindow.cs:3139) were invisible to spheres on the indoor
side of a doorway threshold — walk-through.

Pre-flight reads found that CellTransit.FindCellSet already adds
outdoor cells to its candidate set when the sphere straddles an
OtherCellId=0xFFFF exit portal (via AddAllOutsideCells triggered by
exitOutside=true inside the indoor-seed BFS). The fix is to stop
filtering those outdoor ids out before iterating, and rename the param
to portalReachableCells to reflect what the set actually contains.

- Q1: Indoor EnvCell.VisibleCellIds is indoor-only in all 16 cottage
  fixtures (low 16 bits ≥ 0x0100). OtherCellId=0xFFFF on portals
  marks "exit to outdoor world" without naming a specific cellId; the
  specific outdoor cell is computed by AddAllOutsideCells from world
  XY when the sphere straddles the exit portal.
- Q2: GameWindow.cs:3139 ShadowObjects.Register for server-spawned
  entities passes no cellScope → default 0u → outdoor 24m grid
  registration. UpdatePosition (line 145) does the same on movement.
  Doors are confirmed outdoor-registered.

Slice 1 makes a smaller change than the spec proposed (no new
parameter; just drop the existing filter), because FindCellSet's
existing exit-portal logic already exposes the needed outdoor cells.
The retail-faithful registration-side BuildShadowCellSet refactor and
the b3ce505 gate removal stay scheduled for slices 2-3.

Verification:
- 24/24 ShadowObjectRegistryTests pass (incl. two new slice 1 tests:
  IndoorPrimary_OutdoorCellInPortalSet_DoorReturned closes #99;
  IndoorPrimary_IndoorOnlyPortalSet_OutdoorRadialStillSkipped
  regression-pins #98)
- 11/11 CellarUpTrajectoryReplayTests pass (LiveCompare_FirstCap_
  FixClosesCottageFloorCap stays green)
- dotnet build AcDream.slnx: 0 errors, 0 warnings
- Pre-existing 6-8 static-state-leakage failures in serial physics
  suite verified unchanged by stash+retest baseline check

Visual verification pending: walk Holtburg cottage doorway from both
sides; door blocks both directions; cellar still climbable.

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

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

@@ -301,4 +301,73 @@ public class ShadowObjectRegistryTests
         Assert.Equal(0x00000004u, inA.State);
         Assert.Equal(0x00000004u, inB.State);
     }
+
+    // -----------------------------------------------------------------------
+    // A6.P4 slice 1 — portalReachableCells set includes outdoor cells
+    // when sphere straddles an exit portal (issue #99)
+    // -----------------------------------------------------------------------
+
+    [Fact]
+    public void GetNearbyObjects_PortalReachableSetIncludesOutdoorCell_IndoorPrimary_DoorReturned()
+    {
+        // A6.P4 slice 1 / issue #99 (2026-05-24): when the player's sphere is
+        // in an indoor cell but its CellTransit.FindCellSet result includes
+        // an outdoor cell (via AddAllOutsideCells triggered by the sphere
+        // straddling an OtherCellId=0xFFFF exit portal), GetNearbyObjects
+        // must return shadows registered in that outdoor cell. Doors are
+        // server-spawned entities registered at GameWindow.cs:3139 with
+        // default cellScope=0u → outdoor 24-m grid registration. Before this
+        // fix, the loop filtered out outdoor cell ids ("skip outdoor ids")
+        // AND #98's primaryCellId gate skipped the radial sweep — net result
+        // was that doors at building thresholds were invisible to spheres
+        // on the indoor side: walk-through.
+        var reg = new ShadowObjectRegistry();
+
+        const uint doorEntityId = 0x000F4244u;
+        reg.Register(doorEntityId, 0x020019FFu, new Vector3(12f, 12f, 50f),
+                     Quaternion.Identity, 1f, OffX, OffY, LbId,
+                     ShadowCollisionType.Cylinder, cylHeight: 2.5f);
+
+        var results = new List<ShadowEntry>();
+        uint doorOutdoorCellId = LbId | 1u;       // outdoor cell where door sits
+        uint vestibuleCellId   = LbId | 0x0145u;  // indoor cell on the other side
+
+        // Sphere is in the vestibule; FindCellSet added the doorway's outdoor
+        // cell via AddAllOutsideCells. Both ids land in portalReachableCells.
+        reg.GetNearbyObjects(
+            new Vector3(12f, 12f, 50f), 5f, OffX, OffY, LbId, results,
+            portalReachableCells: new[] { vestibuleCellId, doorOutdoorCellId },
+            primaryCellId: vestibuleCellId);
+
+        Assert.Contains(results, e => e.EntityId == doorEntityId);
+    }
+
+    [Fact]
+    public void GetNearbyObjects_IndoorPrimary_IndoorOnlyPortalSet_OutdoorRadialStillSkipped()
+    {
+        // Regression check for issue #98: when the FindCellSet result holds
+        // only indoor cells (sphere not near an exit portal — e.g. deep in
+        // a cellar), the radial outdoor sweep must stay skipped so the
+        // landblock-baked cottage GfxObj (registered at outdoor cellScope=0)
+        // is NOT returned to a sphere in the cellar EnvCell. Otherwise the
+        // head sphere bumps the cottage's downward-facing floor poly from
+        // below and caps the cellar ascent at world Z≈92.7.
+        var reg = new ShadowObjectRegistry();
+
+        const uint cottageEntityId = 0xA9B47900u;
+        reg.Register(cottageEntityId, 0x01000A2Bu, new Vector3(12f, 12f, 90f),
+                     Quaternion.Identity, 5.5f, OffX, OffY, LbId);
+
+        var results = new List<ShadowEntry>();
+        uint cellarCellId = LbId | 0x0146u;
+
+        // Sphere is in the cellar; FindCellSet returned indoor-only set
+        // (no exit portal nearby).
+        reg.GetNearbyObjects(
+            new Vector3(12f, 12f, 50f), 5.5f, OffX, OffY, LbId, results,
+            portalReachableCells: new[] { cellarCellId },
+            primaryCellId: cellarCellId);
+
+        Assert.DoesNotContain(results, e => e.EntityId == cottageEntityId);
+    }
 }