Problem

MCP (Model Context Protocol) adapters were failing with TypeError: unhashable type: 'list' when processing tool schemas from MCP servers that returned malformed JSON schemas with non-hashable items in the required field.

The error occurred when trying to use MCP servers like the PowerPoint MCP with configuration:

{
  "powerpoint": {
    "command": "uv",
    "args": ["--directory", "/path/to/powerpoint", "run", "powerpoint", "--folder-path", "/path/to/decks_folder"]
  }
}

Root Cause

The issue was in autogen_core.utils._json_to_pydantic.py where set() operations were used to deduplicate required field names. When MCP servers returned schemas with malformed required fields containing lists or dictionaries, these operations would fail:

# This would crash if required contained unhashable items
merged["required"] = list(set(merged["required"]))  # Line 159, 267, 297
required_fields = set(schema.get("required", []))   # Line 271

Example problematic schema:

{
    "type": "object",
    "properties": {
        "folder_path": {"type": "string"},
        "options": {"type": "array", "items": {"type": "string"}}
    },
    "required": ["folder_path", ["options"]]  # <- List in required causes error
}

Solution

1. Added safe deduplication function that filters out non-hashable items:

   def _safe_deduplicate_required(required_list: List[Any]) -> List[str]:
       """Safely deduplicate required list by filtering out non-hashable items."""
       hashable_items = []
       for item in required_list:
           if isinstance(item, str):
               hashable_items.append(item)
           elif isinstance(item, (int, float, bool)):
               hashable_items.append(str(item))
           # Skip unhashable items like lists, dicts, etc.
       return list(set(hashable_items))

2. Updated all problematic locations to use the safe deduplication function

3. Added comprehensive test coverage for various malformed schema scenarios

Behavior

• Before: MCP adapters crashed with unhashable type error
• After: Malformed schemas are processed gracefully, only valid string field names are preserved as required
• Backward compatibility: All existing valid schemas continue to work exactly as before

Testing

Added test_unhashable_required_fields_handling() test case covering:

• Direct schemas with lists in required fields
• allOf schemas with unhashable required items
• Nested schemas with mixed types in required fields

All tests pass and the PowerPoint MCP scenario from the issue now works correctly.

Fixes #6723.

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