fix(lib): keep description and title beside $ref in transform_schema

src/anthropic/lib/_parse/_transform.py

@@ -94,6 +94,14 @@ def transform_schema(
     ref = json_schema.pop("$ref", None)
     if ref is not None:
         strict_schema["$ref"] = ref
+        # Pydantic places Field(description=...) / title beside $ref for
+        # enum and model fields; the API accepts and follows them.
+        description = json_schema.pop("description", None)
+        if description is not None:
+            strict_schema["description"] = description
+        title = json_schema.pop("title", None)
+        if title is not None:
+            strict_schema["title"] = title
         return strict_schema
 
     type_: Optional[SupportedTypes] = json_schema.pop("type", None)

tests/lib/_parse/test_transform.py

@@ -40,6 +40,41 @@ def test_ref_schema_with_defs():
     )
 
 
+def test_ref_schema_preserves_sibling_description():
+    # Pydantic puts Field(description=...) beside $ref for enum/model fields.
+    schema = {
+        "$ref": "#/$defs/Level",
+        "description": "Always choose low.",
+        "$defs": {
+            "Level": {
+                "type": "string",
+                "enum": ["high", "low"],
+                "title": "Level",
+            }
+        },
+    }
+    result = transform_schema(schema)
+    assert result == snapshot(
+        {
+            "$defs": {
+                "Level": {
+                    "type": "string",
+                    "enum": ["high", "low"],
+                    "title": "Level",
+                }
+            },
+            "$ref": "#/$defs/Level",
+            "description": "Always choose low.",
+        }
+    )
+
+
+def test_ref_schema_preserves_sibling_title():
+    schema = {"$ref": "#/$defs/Level", "title": "confidence"}
+    result = transform_schema(schema)
+    assert result == snapshot({"$ref": "#/$defs/Level", "title": "confidence"})
+
+
 def test_anyof_schema():
     schema = {
         "anyOf": [