Fix DiscriminatedUnionMixin issues with Pydantic C bindings

openhands-sdk/openhands/sdk/mcp/tool.py

@@ -186,7 +186,9 @@ def action_from_arguments(self, arguments: dict[str, Any]) -> MCPToolAction:
         # Use exclude_none to avoid injecting nulls back to the call
         # Exclude DiscriminatedUnionMixin fields (e.g., 'kind') as they're
         # internal to OpenHands and not part of the MCP tool schema
-        exclude_fields = set(DiscriminatedUnionMixin.model_fields.keys())
+        exclude_fields = set(DiscriminatedUnionMixin.model_fields.keys()) | set(
+            DiscriminatedUnionMixin.model_computed_fields.keys()
+        )
         sanitized = validated.model_dump(exclude_none=True, exclude=exclude_fields)
         return MCPToolAction(data=sanitized)
 

openhands-sdk/openhands/sdk/tool/schema.py

@@ -121,9 +121,12 @@ def to_mcp_schema(cls) -> dict[str, Any]:
         # so it is fully compatible with MCP tool schema
         result = _process_schema_node(full_schema, full_schema.get("$defs", {}))
 
-        # Remove 'kind' from properties if present (discriminator field, not for LLM)
-        EXCLUDE_FIELDS = DiscriminatedUnionMixin.model_fields.keys()
-        for f in EXCLUDE_FIELDS:
+        # Remove discriminator fields from properties (not for LLM)
+        # Need to exclude both regular fields and computed fields (like 'kind')
+        exclude_fields = set(DiscriminatedUnionMixin.model_fields.keys()) | set(
+            DiscriminatedUnionMixin.model_computed_fields.keys()
+        )
+        for f in exclude_fields:
             if "properties" in result and f in result["properties"]:
                 result["properties"].pop(f)
                 # Also remove from required if present