fix: Handle list values in Gemini schema sanitization

The schema sanitization utility now recursively processes list items, ensuring that properties with list values (e.g., "required") are correctly handled and not altered.

Close #4363

Co-authored-by: George Weale <gweale@google.com>
PiperOrigin-RevId: 867663267

src/google/adk/tools/_gemini_schema_util.py

@@ -142,9 +142,19 @@ def _dereference_schema(schema: dict[str, Any]) -> dict[str, Any]:
 
 
 def _sanitize_schema_formats_for_gemini(
-    schema: dict[str, Any], preserve_null_type: bool = False
-) -> dict[str, Any]:
-  """Filters the schema to only include fields that are supported by JSONSchema."""
+    schema: Any, preserve_null_type: bool = False
+) -> Any:
+  """Filters schemas to only include fields supported by JSONSchema."""
+  if isinstance(schema, list):
+    return [
+        _sanitize_schema_formats_for_gemini(
+            item, preserve_null_type=preserve_null_type
+        )
+        for item in schema
+    ]
+  if not isinstance(schema, dict):
+    return schema
+
   supported_fields: set[str] = set(_ExtendedJSONSchema.model_fields.keys())
   # Gemini rejects schemas that include `additionalProperties`, so drop it.
   supported_fields.discard("additional_properties")
@@ -152,7 +162,7 @@ def _sanitize_schema_formats_for_gemini(
   list_schema_field_names: set[str] = {
       "any_of",  # 'one_of', 'all_of', 'not' to come
   }
-  snake_case_schema = {}
+  snake_case_schema: dict[str, Any] = {}
   dict_schema_field_names: tuple[str, ...] = (
       "properties",
       "defs",

tests/unittests/tools/test_gemini_schema_util.py

@@ -579,6 +579,20 @@ class TestToGeminiSchema:
         "null",
     ]
 
+  def test_sanitize_schema_formats_for_gemini_with_list_property_value(self):
+    schema = {
+        "type": "object",
+        "properties": {
+            "required": ["sql"],
+            "sql": {"type": "string"},
+        },
+    }
+
+    sanitized = _sanitize_schema_formats_for_gemini(schema)
+
+    assert sanitized["properties"]["required"] == ["sql"]
+    assert sanitized["properties"]["sql"]["type"] == "string"
+
   def test_sanitize_schema_formats_for_gemini_nullable(self):
     openapi_schema = {
         "properties": {