fix(agentstudio): let copy_with retune a forward-compat field

copy_with validated its keywords against _fields only, so a key the server
adds and this SDK does not know yet could ride along a copy but could not be
changed: ModelConfig(id="x", vendor="qwen").copy_with(vendor="other") raised
"unknown model config field", even though vendor was in the payload.

Validate against _fields plus what the config actually carries. The guard
keeps its teeth where it matters: a typo (temp=0.5) and inventing a wire field
out of thin air (ModelConfig(id="x").copy_with(vendor="y")) still raise.

Author: foleydang

dashscope/agentstudio/types/models.py

@@ -468,9 +468,11 @@ def copy_with(self, **changes: Any) -> "ModelConfig":
         """Copy with ``changes`` applied (``None`` drops a field).
 
         Update replaces the whole config, so this changes one knob without
-        clearing the rest.
+        clearing the rest.  A name outside :attr:`_fields` has to be carried
+        by this config already, so a forward-compat field can be retuned and
+        a typo still cannot.
         """
-        unknown = set(changes) - set(self._fields)
+        unknown = set(changes) - set(self._fields) - set(self.to_dict())
         if unknown:
             raise ValueError(
                 "unknown model config field(s): " + ", ".join(sorted(unknown)),

tests/unit/test_agentstudio_models.py

@@ -268,13 +268,20 @@ def test_model_config_copy_with_can_drop_and_reject_typos():
 
 
 def test_model_config_unknown_fields_survive_copy_with():
-    """Unknown (forward-compat) fields survive copy_with."""
+    """Forward-compat fields survive copy_with and can be retuned."""
     config = ModelConfig(id="qwen3-max", vendor="qwen")
     assert config.copy_with(temperature=0.5).to_dict() == {
         "id": "qwen3-max",
         "vendor": "qwen",
         "temperature": 0.5,
     }
+    assert config.copy_with(vendor="other").to_dict() == {
+        "id": "qwen3-max",
+        "vendor": "other",
+    }
+    # still not a way to invent wire fields: neither known nor carried
+    with pytest.raises(ValueError, match="unknown model config field"):
+        config.copy_with(vendorx="nope")
 
 
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