feat(client): add validate_structured_output option to ClientSession#2667
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Closes modelcontextprotocol#2626. Real-world MCP servers occasionally return structured_content that does not match their advertised outputSchema. The client currently raises a RuntimeError and drops the result, leaving the caller no escape hatch. This adds a validate_structured_output keyword on ClientSession and Client (default True, so existing behavior is preserved) that lets callers opt out of strict validation when interoperating with non-conformant servers. When validation is disabled, the client logs a debug message and returns the result unchanged. Tests cover both the default-on and opt-out modes.
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Closes #2626.
Real-world MCP servers occasionally return structured_content that does not match their advertised outputSchema. The client currently raises a RuntimeError and drops the result, leaving the caller no escape hatch. This adds a
validate_structured_outputkeyword onClientSessionandClient(defaultTrue, so existing behavior is preserved) that lets callers opt out of strict validation when interoperating with non-conformant servers.When validation is disabled, the client logs a debug message and returns the result unchanged. The motivating case in the issue is a server whose output schema lists a closed set of string literals but is missing one of the values it actually emits; the structured content is otherwise usable and is better surfaced to the caller than dropped.
Tests cover both the default-on path (still raises) and the opt-out path (returns the invalid structured_content and emits a debug log).