fix(models): resolve ToolReferenceContentBlock forward reference causing 422 on tool_result validation

[zouchao]

Summary

• Fix Pydantic v2 forward reference resolution for ToolReferenceContentBlock, which caused 422 validation errors when Claude Code sends tool_reference blocks inside tool_result content

Problem

Claude Code v2.1+ uses the ToolSearch deferred tool mechanism, which places tool_reference content blocks inside tool_result messages:

{
  "type": "tool_result",
  "tool_use_id": "tooluse_xxx",
  "content": [
    {"type": "tool_reference", "tool_name": "mcp__codebase-memory-mcp__index_repository"}
  ]
}

ToolResultContentBlock.content is typed as:
content: Optional[Union[str, List[Union["TextContentBlock", "ImageContentBlock", "ToolReferenceContentBlock"]]]]

However, Pydantic v2 never resolved the "ToolReferenceContentBlock" forward reference string into the actual class. At validation time, the Union only recognized TextContentBlock and ImageContentBlock, rejecting tool_reference blocks with a 422 error.

Solution

Added model_rebuild() calls at the end of models_anthropic.py after all classes are defined:

ToolResultContentBlock.model_rebuild()
AnthropicMessage.model_rebuild()

This forces Pydantic v2 to resolve all forward reference strings in Union type annotations, allowing tool_reference blocks to pass validation correctly.

Test plan

• Validated payload containing tool_reference inside tool_result now parses successfully
• Existing test suite passes (235 passed)

[cla-bot]

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[zouchao]

I have read the CLA and I accept its terms

[ankitcharolia]

@zouchao @sean-aligntech could you give a try to this gateway: https://github.com/ankitcharolia/kiro-gateway

It works quite well with All AI harness and actively being developed. The most important thing is that it is ACP compliant