[Partner Nodes] fix(GPT Image): make custom_width/custom_height optional

OpenAIGPTImageNodeV2 declared the gpt-image-2 custom size widgets as
required nested inputs, so a prompt that picked a preset size and omitted
them failed validation with required_input_missing. execute() already
reads both with a 1024 default, and the deprecated OpenAIGPTImage1 node
in the same file already marks them optional.

comfy_api_nodes/nodes_openai.py

@@ -747,6 +747,7 @@ class OpenAIGPTImageNodeV2(IO.ComfyNode):
                                     max=3840,
                                     step=16,
                                     tooltip="Used only when `size` is 'Custom'. Must be a multiple of 16.",
+                                    optional=True,
                                 ),
                                 IO.Int.Input(
                                     "custom_height",
@@ -755,6 +756,7 @@ class OpenAIGPTImageNodeV2(IO.ComfyNode):
                                     max=3840,
                                     step=16,
                                     tooltip="Used only when `size` is 'Custom'. Must be a multiple of 16.",
+                                    optional=True,
                                 ),
                                 IO.Combo.Input(
                                     "background",

tests-unit/comfy_api_test/gpt_image_size_inputs_test.py

@@ -0,0 +1,27 @@
+from comfy_api.latest._io import get_finalized_class_inputs
+from comfy_api_nodes.nodes_openai import OpenAIGPTImageNodeV2
+
+
+def _finalized_inputs(live_inputs):
+    class_inputs, _, _ = get_finalized_class_inputs(
+        OpenAIGPTImageNodeV2.INPUT_TYPES(), live_inputs
+    )
+    return class_inputs
+
+
+def test_gpt_image_2_custom_size_inputs_are_optional():
+    """A preset `size` must not require the custom width/height widgets to be present."""
+    class_inputs = _finalized_inputs({"model": "gpt-image-2", "model.size": "1536x1024"})
+
+    assert "model.custom_width" not in class_inputs["required"]
+    assert "model.custom_height" not in class_inputs["required"]
+    assert "model.custom_width" in class_inputs["optional"]
+    assert "model.custom_height" in class_inputs["optional"]
+    assert "model.size" in class_inputs["required"]
+
+
+def test_gpt_image_legacy_models_have_no_custom_size_inputs():
+    for model in ("gpt-image-1", "gpt-image-1.5"):
+        class_inputs = _finalized_inputs({"model": model, "model.size": "1536x1024"})
+        assert "model.custom_width" not in class_inputs["required"]
+        assert "model.custom_width" not in class_inputs["optional"]