fix(phys): #106 — outdoor membership crosses landblock boundaries (LandDefs global-lcoord port)

The player's outdoor cell froze at the last in-block cell the moment they
walked over a landblock boundary (10,449-frame playerCell freeze in the
2026-06-09 capture; whole neighbouring-block interiors unenterable, plus
the running-distortion from the stale render anchor). Root cause: the
add_all_outside_cells port clamped BOTH the candidate proposal and the
find_cell_list containing-cell pick to the current landblock's 8x8 grid,
in a frame that silently assumed the current block sits at world origin.
One step over the line -> zero candidates -> FindCellSet returns
currentCellId forever.

Retail has no such clamp. Its cell math runs in a GLOBAL landcell grid
(lcoord 0..2039 spanning the map): get_outside_lcoord = blockid_to_lcoord
+ floor(blockLocalPos/24) with no bounds besides the map edge, and
lcoord_to_gid re-derives the landblock id from the lcoord's upper bits —
crossings are inherent, never special-cased.

The fix, decomp-cited throughout:
- New AcDream.Core.Physics.LandDefs: in_bounds (pc:68509),
  blockid_to_lcoord (pc:68520), inbound_valid_cellid (pc:163438),
  gid_to_lcoord (pc:163500), lcoord_to_gid (pc:171859),
  get_outside_lcoord (pc:438690), adjust_to_outside (pc:438719).
  Cross-checked against ACE LandDefs.cs; three artifacts documented and
  avoided: BN's int8_t mis-render of block_y, BN's dropped 192f
  BlockLength constant, and ACE add_cell_block's "FIXME!" same-block
  guard (an ACE divergence, not retail).
- CellTransit.AddAllOutsideCells rewritten as the faithful sphere
  variant (pc:317499 @0x00533630): adjust_to_outside re-seats the
  (cell, position) pair cross-block, check_add_cell_boundary (pc:317229)
  adds up to 3 neighbours by global lcoord, add_outside_cell (pc:317056)
  has no same-block filter. adjust_to_outside failure breaks the sphere
  loop (pc:533699 verbatim).
- BuildCellSetAndPickContaining: the outdoor containing-cell pick is now
  the global XY-column under the sphere centre (AdjustToOutside), not
  the [0,8)-clamped current-prefix reconstruction. Interior-wins order
  and current-cell-first hysteresis unchanged.
- World->block-local frame conversion via the landblock origin already
  registered in CellGraph (new TryGetTerrainOrigin); Zero fallback
  preserves the legacy anchor-block assumption for unregistered terrain.
- Cross-landblock building entry comes free: the candidate snapshot now
  contains neighbour-block landcells, so GetBuilding/CheckBuildingTransit
  fire for cottages across the line (the capture's one failing entry).

Investigated FIRST per the pickup brief: the b3ce505 #98 stopgap gate is
definitively exonerated — it is a collision-object query gate that fires
only for indoor primary cells; no membership path touches
ShadowObjectRegistry.

Tests: 31 new (25 LandDefs conformance incl. capture-geometry goldens
0xA9B40031 -> 0xA9B30038/0xA9B30034 and the northbound return; 4
AddAllOutsideCells cross-block; 3 FindCellSet membership goldens incl.
the non-anchor-frame origin conversion). Full suite: 294+218+420 green;
Core 1369 green + the 4 pre-existing door/#99-era failures + 1 skip
(unchanged from baseline).

Pseudocode + artifact notes:
docs/research/2026-06-09-landdefs-outside-cells-pseudocode.md.
Remaining acceptance: live boundary walk with ACDREAM_PROBE_CELL=1
(ISSUES.md #106).

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

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

@@ -159,6 +159,75 @@ public class CellTransitFindCellSetTests
         Assert.Contains(0xA9B40001u, cellSet);
     }
 
+    // ──────────────────────────────────────────────────────────────────
+    // #106 — outdoor membership across landblock boundaries.
+    // Retail's add_all_outside_cells + the find_cell_list pick run in the
+    // GLOBAL landcell grid (LandDefs lcoords); crossing a landblock boundary
+    // is inherent. The pre-#106 port clamped both to the current block's 8×8
+    // grid → zero candidates one step over the line → membership frozen
+    // (the 10,449-frame playerCell freeze in flap-105-capture.log).
+    // ──────────────────────────────────────────────────────────────────
+
+    [Fact]
+    public void OutdoorSeed_CrossesLandblockBoundary_South()
+    {
+        // The #106 acceptance golden: walking south out of A9B4, the outdoor
+        // cell must advance to the southern neighbour block's cell. Anchor
+        // frame (no registered terrain → origin Zero): world y = -0.2 is
+        // 0.2 m into A9B3's row 7 under x=150 → cell 0xA9B30038.
+        var cache = new PhysicsDataCache();
+
+        uint containing = CellTransit.FindCellSet(
+            cache, new Vector3(150f, -0.2f, 0f), sphereRadius: 0.5f,
+            currentCellId: 0xA9B40031u,
+            out var cellSet);
+
+        Assert.Equal(0xA9B30038u, containing);
+        Assert.Contains(0xA9B30038u, cellSet);
+        Assert.Contains(0xA9B40031u, cellSet);   // +Y neighbour still in the set
+    }
+
+    [Fact]
+    public void OutdoorSeed_NearBoundaryButInside_StaysCurrent()
+    {
+        // 0.2 m NORTH of the boundary: the candidate set includes the A9B3
+        // neighbour (sphere overlaps it) but the centre column is still the
+        // current cell — membership must NOT flip early (single clean flip
+        // at the line, matching the capture's 96/96 within-block behaviour).
+        var cache = new PhysicsDataCache();
+
+        uint containing = CellTransit.FindCellSet(
+            cache, new Vector3(150f, 0.2f, 0f), sphereRadius: 0.5f,
+            currentCellId: 0xA9B40031u,
+            out var cellSet);
+
+        Assert.Equal(0xA9B40031u, containing);
+        Assert.Contains(0xA9B30038u, cellSet);
+    }
+
+    [Fact]
+    public void OutdoorSeed_NonAnchorBlock_UsesRegisteredTerrainOrigin()
+    {
+        // Northbound return: the player's current cell is in A9B3 (origin
+        // (0, -192) registered via CellGraph terrain — the production path).
+        // World y = +1 is 1 m back into the anchor block A9B4; the pick must
+        // convert through A9B3's origin (block-local y = 193) and advance to
+        // 0xA9B40031. Pre-#106 the world frame was silently assumed
+        // block-local, which is wrong for every non-anchor block.
+        var cache = new PhysicsDataCache();
+        cache.CellGraph.RegisterTerrain(
+            0xA9B30000u,
+            new TerrainSurface(new byte[81], new float[256]),
+            new Vector3(0f, -192f, 0f));
+
+        uint containing = CellTransit.FindCellSet(
+            cache, new Vector3(150f, 1f, 0f), sphereRadius: 0.5f,
+            currentCellId: 0xA9B30038u,
+            out _);
+
+        Assert.Equal(0xA9B40031u, containing);
+    }
+
     // ──────────────────────────────────────────────────────────────────
     // Membership hysteresis — the R1-flap root cause.
     // Retail CObjCell::find_cell_list adds the CURRENT cell at index 0