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>

src/AcDream.Core/World/Cells/CellGraph.cs

@@ -27,6 +27,25 @@ public sealed class CellGraph
     public void RegisterTerrain(uint landblockPrefix, TerrainSurface terrain, Vector3 worldOrigin)
         => _terrain[landblockPrefix & 0xFFFF0000u] = (terrain, worldOrigin);
 
+    /// <summary>
+    /// World origin (SW corner) of the landblock containing <paramref name="id"/>,
+    /// as registered by <see cref="RegisterTerrain"/>. Issue #106: converts the
+    /// floating-world-frame sphere coords into retail's block-local frame for the
+    /// <see cref="LandDefs"/> lcoord math. False (origin zero) when the landblock
+    /// has no registered terrain — callers fall back to the legacy anchor-block
+    /// assumption (world frame == block-local frame).
+    /// </summary>
+    public bool TryGetTerrainOrigin(uint id, out Vector3 origin)
+    {
+        if (_terrain.TryGetValue(id & 0xFFFF0000u, out var t))
+        {
+            origin = t.Origin;
+            return true;
+        }
+        origin = Vector3.Zero;
+        return false;
+    }
+
     public void RemoveLandblock(uint landblockPrefix)
     {
         uint lb = landblockPrefix & 0xFFFF0000u;