Support for OpenAI Apps SDK

[BrandonShar]

Description

OpenAI released their Apps SDK this past Monday along with an example repo for implementing this in FastMCP.

The example repo required creating custom handlers in order to support the _meta field that the Apps SDK depends on in several places. This field is part of the protocol, but not handled via the SDK.

This issue is to consolidate the features and existing PRs that are necessary for full support.

• Add Meta to Tool Definitions feat: add tool metadata in FastMCP.tool decorator #1463
• Allow Meta to be returned in Tool Call payloads Allow CallToolResult to be returned directly to support _meta field for OpenAI Apps #1459
• Add Meta to Resource Definitions

References

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

https://github.com/openai/openai-apps-sdk-examples/blob/main/pizzaz_server_python/main.py

[alexanderreiff]

I took inspiration from #1459 and implemented a similar solution for the resource _meta needs: #1476