Add missing spatial_hash.insert() in set_grid() grid transfer, closes #274

When transferring an entity to a new grid via entity.grid = new_grid,
the entity was removed from the old grid's spatial hash but never
inserted into the new one. This made it invisible to spatial queries
on the destination grid.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/UIEntity.cpp

@@ -795,6 +795,7 @@ int UIEntity::set_grid(PyUIEntityObject* self, PyObject* value, void* closure)
     if (self->data->grid != new_grid) {
         new_grid->entities->push_back(self->data);
         self->data->grid = new_grid;
+        new_grid->spatial_hash.insert(self->data);  // #274
 
         // Resize gridstate to match new grid dimensions
         self->data->ensureGridstate();

tests/regression/issue_274_set_grid_spatial_hash_test.py

@@ -0,0 +1,74 @@
+"""Regression test: set_grid() missing spatial hash insert (#274).
+
+Bug: When transferring an entity to a new grid via entity.grid = new_grid,
+the entity was removed from the old grid's spatial hash but NOT inserted
+into the new grid's spatial hash. This made the entity invisible to
+spatial queries on the new grid.
+
+Fix: Added spatial_hash.insert() call after adding entity to new grid.
+"""
+import mcrfpy
+import sys
+
+def test_grid_transfer_spatial_hash():
+    """Entity transferred between grids appears in new grid's spatial hash"""
+    grid1 = mcrfpy.Grid(grid_size=(20, 20))
+    grid2 = mcrfpy.Grid(grid_size=(20, 20))
+    entity = mcrfpy.Entity(grid_pos=(5, 5), grid=grid1)
+
+    # Verify found on grid1
+    found1 = grid1.entities_in_radius((5.0, 5.0), 1.0)
+    assert len(found1) == 1, f"Expected 1 on grid1, found {len(found1)}"
+
+    # Transfer to grid2
+    entity.grid = grid2
+
+    # Should NOT be on grid1 anymore
+    found1_after = grid1.entities_in_radius((5.0, 5.0), 1.0)
+    assert len(found1_after) == 0, f"Expected 0 on grid1 after transfer, found {len(found1_after)}"
+
+    # Should be on grid2
+    found2 = grid2.entities_in_radius((5.0, 5.0), 1.0)
+    assert len(found2) == 1, f"Expected 1 on grid2 after transfer, found {len(found2)}"
+
+    print("  PASS: grid_transfer_spatial_hash")
+
+def test_set_grid_none_removes_from_hash():
+    """Setting entity.grid = None removes from spatial hash"""
+    grid = mcrfpy.Grid(grid_size=(20, 20))
+    entity = mcrfpy.Entity(grid_pos=(5, 5), grid=grid)
+
+    found = grid.entities_in_radius((5.0, 5.0), 1.0)
+    assert len(found) == 1
+
+    entity.grid = None
+
+    found = grid.entities_in_radius((5.0, 5.0), 1.0)
+    assert len(found) == 0, f"Expected 0 after grid=None, found {len(found)}"
+    print("  PASS: set_grid_none_removes_from_hash")
+
+def test_multiple_transfers():
+    """Entity survives multiple grid transfers with correct spatial hash"""
+    grids = [mcrfpy.Grid(grid_size=(20, 20)) for _ in range(4)]
+    entity = mcrfpy.Entity(grid_pos=(3, 3), grid=grids[0])
+
+    for i in range(1, 4):
+        entity.grid = grids[i]
+
+        # Should be on new grid
+        found = grids[i].entities_in_radius((3.0, 3.0), 1.0)
+        assert len(found) == 1, f"Expected 1 on grid[{i}], found {len(found)}"
+
+        # Should NOT be on previous grid
+        found_prev = grids[i-1].entities_in_radius((3.0, 3.0), 1.0)
+        assert len(found_prev) == 0, f"Expected 0 on grid[{i-1}], found {len(found_prev)}"
+
+    print("  PASS: multiple_transfers")
+
+
+print("Testing set_grid() spatial hash operations (#274)...")
+test_grid_transfer_spatial_hash()
+test_set_grid_none_removes_from_hash()
+test_multiple_transfers()
+print("PASS: all set_grid spatial hash tests passed")
+sys.exit(0)