[Server] Add meta to addPrompt and addResourceTemplate methods

[bb-c24]

Summary

Add missing meta parameter to Builder::addResourceTemplate() and Builder::addPrompt() methods to complete the metadata support across all registration methods.

Motivation and Context

The ResourceTemplate and Prompt schemas support a _meta field for passing additional metadata. However, the Builder::addResourceTemplate() and Builder::addPrompt() methods didn't expose this parameter, creating an inconsistency with other registration methods like addTool() and addResource() which already support meta.

This change completes the metadata support across all manual registration methods, providing a consistent API for users to attach arbitrary metadata to any MCP element.

How Has This Been Tested?

• Verified that the meta parameter is properly added to both methods
• Confirmed that the compact() calls include the new meta parameter
• Checked that the parameters are optional with null defaults for backward compatibility
• Ensured consistency with existing addTool() and addResource() implementations

Breaking Changes

None. This is a backward-compatible change:

• The meta parameter is optional with a default value of null
• Existing code will continue to work without modifications
• The meta field is only included when explicitly provided

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

Changes made:

1. Added meta parameter to Builder::addResourceTemplate() method
2. Added meta parameter to Builder::addPrompt() method
3. Updated compact() calls to include meta in both methods

This completes the metadata support that was previously added to addTool() and addResource() in PR #144, ensuring all manual registration methods have feature parity with the underlying schema classes.

Note: The corresponding PHPDoc type definitions and ArrayLoader changes will need to be updated separately to fully support these fields throughout the registration pipeline.

[chr-hertel]

Thanks for that! 👍

[chr-hertel]

that setup just doesn't feel that robust, but that's not on you - your basically just cleaning up - thanks for that!

[bb-c24]

@chr-hertel There was also an issue because meta was not null-coalesced also when using addPrompt it was not added to the prompt array, which then caused that undefined key error.