Set IsError on CallToolResponse to true when result is ErrorContent

[Astaggrock]

Currently when providing an ErrorContent type as the result to a tool the IsError property on the resulting CallToolResponse is not set to true.

Motivation and Context

To allow the calling client to understand the response is an error the IsError property should be set to true when an error has occurred within the tool invocation. Unlike throwing an exception this can protect any potential unwanted information being reported from the exception details.

How Has This Been Tested?

Adjusted sample tools to confirm IsError is being set to true when an ErrorContent result is returned

Breaking Changes

No

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

Additional context

[stephentoub]

Thanks.