[Bug]: `mcp.enabled` defaults are not working

[JerryNixon]

What?

When mcp.enabled is NOT in the config, but we use the default value instead, MCP does not work.

Important

Config properties with default values should not be required to be in the config to work properly.

/mcp output:

{
  "error": {
    "code": "GlobalMcpEndpointDisabled", // this is the error
    "message": "Route mcp was not found.",
    "status": 404
  }
}

/health output:

{
  "status": "Healthy",
  "version": "2.0.0",
  "app-name": "dab_oss_2.0.0",
  "timestamp": "2026-03-15T21:04:32.5518362Z",
  "currentRole": "anonymous",
  "configuration": {
    "rest": true,
    "graphql": true,
    "mcp": true, // it says true but it does not work!
    "caching": false,
    "telemetry": false,
    "mode": "Development"
  },
  "checks": [ [snip] ]
}

Workaround

Include mcp.enabled=true in the config file.

[JerryNixon]

The bug is in McpEndpointRouteBuilderExtensions.TryGetMcpOptions(). When mcp.enabled is not in the config file, runtimeConfig.Runtime.Mcp is null. This method returns false, and the caller in MapDabMcp bails out early without mapping the MCP endpoint.