fix(loaders): non-list features and blank/non-string entries fail cleanly

features was popped and only re-added when it was a list, so a bare
string (or dict/null) loaded with zero feats - silent data loss. Now a
present non-list features raises CombatantLoadError, and the list
resolution adopts an accept-string-or-error contract: non-string or
blank entries raise instead of being silently dropped.

tests/test_combatant_loader.py

@@ -76,22 +76,24 @@ class TestResolveFeat:
 
 
 class TestResolveFeatures:
-    def test_filters_empty_and_whitespace(self) -> None:
-        result = _resolve_features(["Power Attack", "", "  ", "Dodge"], 1)
-        assert len(result) == 2
-        assert result[0] is POWER_ATTACK
-        assert result[1] is DODGE
+    def test_blank_entry_raises(self, tmp_path: Path) -> None:
+        with pytest.raises(CombatantLoadError, match="non-empty feat name strings"):
+            _resolve_features(["Power Attack", "", "  ", "Dodge"], 1, tmp_path)
 
-    def test_filters_non_strings(self) -> None:
+    def test_non_string_entry_raises(self, tmp_path: Path) -> None:
         raw: list[Json] = ["Iron Will", 42, None, True]
-        result = _resolve_features(raw, 1)
-        assert len(result) == 1
+        with pytest.raises(CombatantLoadError, match="non-empty feat name strings"):
+            _resolve_features(raw, 1, tmp_path)
 
-    def test_empty_list(self) -> None:
-        assert _resolve_features([], 1) == []
+    def test_valid_strings_resolve(self, tmp_path: Path) -> None:
+        result = _resolve_features(["Power Attack", "Dodge"], 1, tmp_path)
+        assert result == [POWER_ATTACK, DODGE]
 
-    def test_all_unknown(self) -> None:
-        result = _resolve_features(["Feat A", "Feat B"], 1)
+    def test_empty_list(self, tmp_path: Path) -> None:
+        assert _resolve_features([], 1, tmp_path) == []
+
+    def test_all_unknown(self, tmp_path: Path) -> None:
+        result = _resolve_features(["Feat A", "Feat B"], 1, tmp_path)
         assert len(result) == 2
         assert all(f.effects == () for f in result)
 
@@ -159,6 +161,26 @@ class TestFeatures:
         c = load_combatant(_write(tmp_path, data))
         assert c.features == []
 
+    def test_string_features_raises(self, tmp_path: Path) -> None:
+        data = _minimal_payload(features="Toughness")
+        with pytest.raises(CombatantLoadError, match="features must be a list"):
+            load_combatant(_write(tmp_path, data))
+
+    def test_dict_features_raises(self, tmp_path: Path) -> None:
+        data = _minimal_payload(features={"a": "Toughness"})
+        with pytest.raises(CombatantLoadError, match="features must be a list"):
+            load_combatant(_write(tmp_path, data))
+
+    def test_null_features_raises(self, tmp_path: Path) -> None:
+        data = _minimal_payload(features=None)
+        with pytest.raises(CombatantLoadError, match="features must be a list"):
+            load_combatant(_write(tmp_path, data))
+
+    def test_non_string_entry_raises(self, tmp_path: Path) -> None:
+        data = _minimal_payload(features=["Toughness", 42])
+        with pytest.raises(CombatantLoadError, match="non-empty feat name strings"):
+            load_combatant(_write(tmp_path, data))
+
 
 class TestSpells:
     def test_spells_passed_through(self, tmp_path: Path) -> None: