[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.

[souvikghosh04]

When the mcp block is omitted from config, RuntimeConfig.IsMcpEnabled returns true (correct), and /health reports MCP enabled. But TryGetMcpOptions in McpEndpointRouteBuilderExtensions.cs does a null check on Runtime.Mcp and skips endpoint registration when it's null and /mcp returns 404.

Additionally, RestService.GetRouteAfterPathBase unconditionally throws GlobalMcpEndpointDisabled for MCP path requests without checking IsMcpEnabled.

Fixes:

1. McpEndpointRouteBuilderExtensions.TryGetMcpOptions: mcpOptions = runtimeConfig?.Runtime?.Mcp ?? new McpRuntimeOptions();
2. RestService.cs: guard with !runtimeConfigProvider.GetConfig().IsMcpEnabled before throwing.