Adding explicit guidance for returning HTTP errors when input is not acceptable, explicitly requiring a 406 status code for unmet Accept header requirements and 400 status for unmet request body requirements.

Motivation and Context

There's varying behavior among SDKs when handling specified Accept header and request body requirements, with at least one returning HTTP status 500 (Internal Server Error) errors instead of 406 or 400 respectively. Status 500 should be used when the reason isn't known, as opposed to cases where the reason is known through explicit header and request body validation.

How Has This Been Tested?

Generated, checked, and verified local preview.

Breaking Changes

Some SDKs will need to update the error they return in the explicitly defined cases.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed