mcp serve help output does not reveal the protocol command

[autocarl]

Summary

When UseMcpServer() registers the hidden MCP protocol passthrough command, the command works but exploratory help output makes it look unavailable.

Reproduction

Using a minimal app with:

var app = ReplApp.Create().UseDefaultInteractive();
app.UseMcpServer();
app.Map("ops status", () => new { Healthy = true }).ReadOnly();
return app.Run(args);

Run:

dotnet run -- mcp --help
dotnet run -- mcp serve --help

Observed output:

Commands:
  (none)

But the command itself works:

dotnet run -- mcp serve

and MCP Inspector can connect when invoked through a wrapper script.

Expected behavior

One of:

• mcp --help / mcp serve --help should reveal the protocol passthrough command in a safe way; or
• docs should explicitly state that mcp serve is intentionally hidden/protocol-passthrough and may not appear in help output.

Why this matters

Coding agents and new users often explore by running --help. If help says (none), they may incorrectly conclude that MCP was not registered.

Environment observed

• Repl.Mcp: 0.10.0 and 0.11.0-dev.56
• .NET SDK: 10.0.301
• OS: Ubuntu 24.04 linux-x64