Tools and resources should support _meta additions

[asklar]

Is your feature request related to a problem? Please describe.
ChatGPT apps rely on having certain _meta fields in tools and resources. AFAICT this is not possible today with the C# SDK.

Describe the solution you'd like
It should be easy to set these via attributes.

Describe alternatives you've considered
n/a

Additional context

• https://developers.openai.com/apps-sdk/build/mcp-server

[joelday]

Beat me to it by 1 minute!

[stephentoub]

This is already supported, e.g.

csharp-sdk/src/ModelContextProtocol.Core/Protocol/Tool.cs

Lines 119 to 126 in d22c5f0

	/// <summary>
	/// Gets or sets metadata reserved by MCP for protocol-level metadata.
	/// </summary>
	/// <remarks>
	/// Implementations must not make assumptions about its contents.
	/// </remarks>
	[JsonPropertyName("_meta")]
	public JsonObject? Meta { get; set; }

. It's just not specifiable directly in the attributes. That's covered by #443 (comment).

[stephentoub]

Addressed in #857