fix(server): skip output schema validation for tool errors#2525
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Genmin wants to merge 1 commit intomodelcontextprotocol:v1.xfrom
Open
fix(server): skip output schema validation for tool errors#2525Genmin wants to merge 1 commit intomodelcontextprotocol:v1.xfrom
Genmin wants to merge 1 commit intomodelcontextprotocol:v1.xfrom
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Summary
Fixes #2429.
When a typed FastMCP tool returns a
CallToolResultwithisError=True, the v1.x server should preserve that error result. Previously,FuncMetadata.convert_result()still validatedstructuredContentagainst the inferred output schema, so error results without structured content raised a Pydantic validation error and replaced the intended tool error.This gates schema validation to non-error
CallToolResultvalues while preserving validation for successful structured tool results.Validation
uv run pytest tests/server/fastmcp/test_func_metadata.py -quv run pytest tests/server/fastmcp -quv run ruff check src/mcp/server/fastmcp/utilities/func_metadata.py tests/server/fastmcp/test_func_metadata.pyuv run pyright src/mcp/server/fastmcp/utilities/func_metadata.py tests/server/fastmcp/test_func_metadata.pygit diff --check