Option to support declarative tool registration activated by version (e.g. "beta") #1557

Is your feature request related to a problem? Please describe.

Currently, there is no clear way to adding new endpoints under test and keeping those from the broader user audience.

This makes incremental rollouts of new tools challenging because it is not possible to easily have some users opt in progressively to receive new features for stability testing.

Describe the solution you'd like

• When tools are registered, allow it to be registered with a version
• Spitballing:
  • Version specification: accept route match (*/vnext/*) or header (x-mcp-version: vnext)
  • Example: [McpServerTool(Name = "my_tool", VersionHeader = "x-mcp-version", VersionMatch = "vnext")]
• This sets up the filter in the middleware automatically and checks incoming headers against the toolset metadata, automatically removing ones that target specific versions; effectively, it says client must transmit the header to see this tool.

Describe alternatives you've considered

Current workaround is to directly manipulate the ToolCollection dynamically:

server.WithListToolsHandler(
    async (context, cancellationToken) =>
    {
        // Resolve HttpContext via DI
        var httpContext = context
            .Services?.GetRequiredService<IHttpContextAccessor>()
            .HttpContext;

        // Check for the specific header
        bool betaEnabled =
            httpContext?.Request.Headers.ContainsKey("x-biblio-enable-beta") ?? false;

        if (!betaEnabled)
        {
            var betaTools =
                context.Server?.ServerOptions?.ToolCollection?.Where(tool =>
                    tool.ProtocolTool.Title?.Contains("(BETA)") ?? false
                )
                ?? [];

            foreach (var tool in betaTools.ToList())
            {
                // 👇 Active removal
                context?.Server?.ServerOptions?.ToolCollection?.Remove(tool);
            }
        }

        return new ListToolsResult
        {
            Tools = [], // Empty; these are additional tools.
        };
    }
);

Additional context

Similar to these issues:

• Version-Based Tool Registration for MCP Server #1216
• Support for Runtime Tool Filtering and/or Multiple MCP Endpoints for Persona-Based Tool Sets in ASP.NET Core #612