Looking at the custom extensions example in the documentation, it seems outdates as

1. it says that mcp prompts are not available yet.
2. points to the 2024 spec
   Given the advanced features added, i think quick fix is to just update that info block
   https://block.github.io/goose/docs/tutorials/custom-extensions