Add an optional stateless Streamable HTTP MCP lab

[jongalloway]

Summary

Add an optional workshop exercise that contrasts the existing stdio MCP server with the MCP C# SDK 2.x stateless Streamable HTTP transport from the 2026-07-28 specification.

Follow-up to #616. The migration epic deliberately kept Parts 5 and 6 on stdio; this issue preserves the strongest next step from that decision.

Learning goals

• Explain why the 2026-07-28 protocol is stateless by default over HTTP.
• Host an MCP server with ModelContextProtocol.AspNetCore 2.2.x and ordinary ASP.NET Core routing.
• Show that protocol version and capabilities travel with each request and no Mcp-Session-Id is required.
• Demonstrate standardized Mcp-Method and Mcp-Name headers.
• Promote one meaningful tool argument with [McpHeader] and explain an intermediary routing scenario.
• Preserve Part 5 stdio as the required fundamentals path.

Proposed workshop fit

Use the optional Part 6 business server. A regional order lookup is a natural scenario for promoting region into Mcp-Param-Region so a gateway or load balancer can route without inspecting the JSON-RPC body.

Acceptance criteria

• The HTTP server uses ModelContextProtocol.AspNetCore and remains stateless by default.
• A runnable client or protocol harness calls the server locally without deployment or authentication prerequisites.
• Tests verify there is no session requirement and inspect standardized method/name headers.
• Tests verify body/header agreement and the HeaderMismatch behavior.
• The exercise explains when stdio remains preferable.
• The optional exercise fits the Part 6 time budget or is clearly marked as follow-on material.
• Release builds are warning-free and documentation lint/link checks pass.

References

• MCP C# SDK 2.0 announcement
• MCP specification revision 2026-07-28