fix(rules): load_map rejects any square_size_ft other than 5 (SRD Measuring Distance: one grid square is 5 feet; the engine's 5-10-5 geometry, step costs and ranges are hard-coded to that scale) - a map declaring 10-ft squares was loaded silently and mis-scaled; now a fail-fast MapValidationError, with reject/accept tests

tests/test_map.py

@@ -73,6 +73,20 @@ def test_rejects_ragged_rows(tmp_path: Path) -> None:
         load_map(_write(tmp_path, body))
 
 
+def test_rejects_non_five_foot_square_size(tmp_path: Path) -> None:
+    """SRD Measuring Distance: one grid square is 5 ft; the engine geometry
+    is hard-coded to that scale, so any other declared size is a load error
+    (fail fast) rather than a silent mis-scaling."""
+    body = _minimal_map().replace('name: "Test"\n', 'name: "Test"\nsquare_size_ft: 10\n')
+    with pytest.raises(MapValidationError, match="square_size_ft must be 5"):
+        load_map(_write(tmp_path, body))
+
+
+def test_accepts_explicit_five_foot_square_size(tmp_path: Path) -> None:
+    body = _minimal_map().replace('name: "Test"\n', 'name: "Test"\nsquare_size_ft: 5\n')
+    assert load_map(_write(tmp_path, body)).square_size_ft == 5
+
+
 def test_rejects_char_missing_from_legend(tmp_path: Path) -> None:
     body = _minimal_map().replace("  #.#\n", "  #x#\n")
     with pytest.raises(MapValidationError):