fix: gate multiselect validation on schema config, improve error message, add tests

Amp-Thread-ID: https://ampcode.com/threads/T-019dad04-a07a-724b-af4d-fbfe98654fdd
Co-authored-by: Amp <amp@ampcode.com>

execution.py

@@ -994,8 +994,8 @@ async def validate_inputs(prompt_id, prompt, item, validated):
                         combo_options = extra_info.get("options", [])
                     else:
                         combo_options = input_type
-                    # MultiCombo sends a list of selected values
-                    if isinstance(val, list):
+                    is_multiselect = extra_info.get("multiselect", False)
+                    if is_multiselect and isinstance(val, list):
                         invalid_vals = [v for v in val if v not in combo_options]
                     else:
                         invalid_vals = [val] if val not in combo_options else []
@@ -1014,7 +1014,7 @@ async def validate_inputs(prompt_id, prompt, item, validated):
                         error = {
                             "type": "value_not_in_list",
                             "message": "Value not in list",
-                            "details": f"{x}: '{invalid_vals}' not in {list_info}",
+                            "details": f"{x}: {', '.join(repr(v) for v in invalid_vals)} not in {list_info}",
                             "extra_info": {
                                 "input_name": x,
                                 "input_config": input_config,

tests-unit/comfy_api_test/multicombo_serialization_test.py

@@ -1,4 +1,4 @@
-from comfy_api.latest._io import MultiCombo
+from comfy_api.latest._io import Combo, MultiCombo
 
 
 def test_multicombo_serializes_multi_select_as_object():
@@ -31,3 +31,48 @@ def test_multicombo_serializes_multi_select_with_placeholder_and_chip():
         "placeholder": "Select providers",
         "chip": True,
     }
+
+
+def test_combo_does_not_serialize_multiselect():
+    """Regular Combo should not have multiselect in its serialized output."""
+    combo = Combo.Input(
+        id="choice",
+        options=["a", "b", "c"],
+    )
+
+    serialized = combo.as_dict()
+
+    # Combo sets multiselect=False, but prune_dict keeps False (not None),
+    # so it should be present but False
+    assert serialized.get("multiselect") is False
+    assert "multi_select" not in serialized
+
+
+def _validate_combo_values(val, combo_options, is_multiselect):
+    """Reproduce the validation logic from execution.py for testing."""
+    if is_multiselect and isinstance(val, list):
+        return [v for v in val if v not in combo_options]
+    else:
+        return [val] if val not in combo_options else []
+
+
+def test_multicombo_validation_accepts_valid_list():
+    options = ["a", "b", "c"]
+    assert _validate_combo_values(["a", "b"], options, True) == []
+
+
+def test_multicombo_validation_rejects_invalid_values():
+    options = ["a", "b", "c"]
+    assert _validate_combo_values(["a", "x"], options, True) == ["x"]
+
+
+def test_multicombo_validation_accepts_empty_list():
+    options = ["a", "b", "c"]
+    assert _validate_combo_values([], options, True) == []
+
+
+def test_combo_validation_rejects_list_even_with_valid_items():
+    """A regular Combo should not accept a list value."""
+    options = ["a", "b", "c"]
+    invalid = _validate_combo_values(["a", "b"], options, False)
+    assert len(invalid) > 0