feat(combat): support multi-cell occupancy for large and larger creatures

tests/test_reach.py

@@ -184,11 +184,17 @@ def test_sword_plus_reach_weapon_union() -> None:
 
 
 def test_large_creature_sword_threatens_disk_radius_2() -> None:
-    """A Large creature (natural reach 10 ft) with a 5 ft sword threatens the disk of radius 2."""
+    """A Large creature (2x2 footprint, natural reach 10 ft) with a 5 ft sword
+    threatens the union of radius-2 disks around each occupied cell."""
     giant = make_combatant("giant", size="Large")
     state = make_state(giant, "players", (3, 3))
     engine = make_engine([state])
-    assert engine._threatened_squares(state) == frozenset(_disk((3, 3), 2))
+    footprint = state.occupied_cells()
+    expected = set()
+    for cell in footprint:
+        expected |= _disk(cell, 2)
+    expected -= footprint
+    assert engine._threatened_squares(state) == frozenset(expected)
 
 
 def test_unknown_size_defaults_to_5ft() -> None: