[BUG] [v0.0.7] cortex-mcp-types ServerCapabilities.experimental accepts scalar values even though MCP requires capability objects

[marvinayisi]

Project

cortex

Description

A server capabilities object whose experimental entry is a scalar number deserializes successfully into ServerCapabilities, even though the 2024 MCP schema requires each experimental capability value to be an object.

Error Message

SERVER_EXPERIMENTAL_SCALAR_PARSE=Ok(ServerCapabilities { experimental: Some({"x": Number(1)}), logging: None, prompts: None, resources: None, tools: None })

Debug Logs

N/A

System Information

Cortex crate: cortex-mcp-types 0.0.7
Commit: 7954d02
Date: 2026-04-10
OS: macOS

Screenshots

https://github.com/marvinayisi/issue-images/blob/main/mcp-server-experimental-scalar-20260410-074112.png

Steps to Reproduce

1. Create a tiny Rust crate depending on cortex-mcp-types from this workspace.
2. Deserialize ServerCapabilities from { "experimental": { "x": 1 } }.
3. Print the parse result.

Expected Behavior

The invalid scalar experimental capability should be rejected.

Actual Behavior

Deserialization succeeds and stores the scalar value under experimental.

Additional Context

• Authoritative spec: https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/refs/heads/main/schema/2024-11-05/schema.ts
• Code path: /Users/odeili/Projects/platform/cortex/src/cortex-mcp-types/src/capabilities.rs
• Duplicate check on 2026-04-10:
• cortex-mcp-types ServerCapabilities experimental scalar