fix: typescript types to be compatible with MCP SDK

[aharvard]

Hi folks! Please let me know if you'd like me to make any adjustments or if you need more info.

This PR proposes a discriminated union type to meet type expectations when creating an MCP server with the MCP typescript SDK.

Here's the error I got when I returned an object created by createHtmlResource() from the SDK's McpServer:

No overload matches this call.
  Overload 1 of 6, '(name: string, description: string, paramsSchemaOrAnnotations: { [x: string]: unknown; title?: string | undefined; readOnlyHint?: boolean | undefined; destructiveHint?: boolean | undefined; idempotentHint?: boolean | undefined; openWorldHint?: boolean | undefined; } | {}, cb: (args: {}, extra: RequestHandlerExtra<...>) => { ...; } | Promise<...>): RegisteredTool', gave the following error.
    Argument of type '() => Promise<{ content: HtmlResourceBlock[]; }>' is not assignable to parameter of type '(args: {}, extra: RequestHandlerExtra<ServerRequest, ServerNotification>) => { [x: string]: unknown; content: ({ [x: string]: unknown; type: "text"; text: string; } | { ...; } | { ...; } | { ...; })[]; _meta?: { ...; } | undefined; structuredContent?: { ...; } | undefined; isError?: boolean | undefined; } | Promise<...'.
      Type 'Promise<{ content: HtmlResourceBlock[]; }>' is not assignable to type '{ [x: string]: unknown; content: ({ [x: string]: unknown; type: "text"; text: string; } | { [x: string]: unknown; type: "image"; data: string; mimeType: string; } | { [x: string]: unknown; type: "audio"; data: string; mimeType: string; } | { ...; })[]; _meta?: { ...; } | undefined; structuredContent?: { ...; } | und...'.
        Type 'Promise<{ content: HtmlResourceBlock[]; }>' is not assignable to type 'Promise<{ [x: string]: unknown; content: ({ [x: string]: unknown; type: "text"; text: string; } | { [x: string]: unknown; type: "image"; data: string; mimeType: string; } | { [x: string]: unknown; type: "audio"; data: string; mimeType: string; } | { ...; })[]; _meta?: { ...; } | undefined; structuredContent?: { ...;...'.
          Type '{ content: HtmlResourceBlock[]; }' is not assignable to type '{ [x: string]: unknown; content: ({ [x: string]: unknown; type: "text"; text: string; } | { [x: string]: unknown; type: "image"; data: string; mimeType: string; } | { [x: string]: unknown; type: "audio"; data: string; mimeType: string; } | { ...; })[]; _meta?: { ...; } | undefined; structuredContent?: { ...; } | und...'.
            Types of property 'content' are incompatible.
              Type 'HtmlResourceBlock[]' is not assignable to type '({ [x: string]: unknown; type: "text"; text: string; } | { [x: string]: unknown; type: "image"; data: string; mimeType: string; } | { [x: string]: unknown; type: "audio"; data: string; mimeType: string; } | { [x: string]: unknown; type: "resource"; resource: { ...; } | { ...; }; })[]'.
                Type 'HtmlResourceBlock' is not assignable to type '{ [x: string]: unknown; type: "text"; text: string; } | { [x: string]: unknown; type: "image"; data: string; mimeType: string; } | { [x: string]: unknown; type: "audio"; data: string; mimeType: string; } | { [x: string]: unknown; type: "resource"; resource: { ...; } | { ...; }; }'.
                  Type 'HtmlResourceBlock' is not assignable to type '{ [x: string]: unknown; type: "resource"; resource: { [x: string]: unknown; text: string; uri: string; mimeType?: string | undefined; } | { [x: string]: unknown; uri: string; blob: string; mimeType?: string | undefined; }; }'.
                    Types of property 'resource' are incompatible.
                      Type '{ uri: string; mimeType: "text/html" | "text/uri-list"; text?: string | undefined; blob?: string | undefined; }' is not assignable to type '{ [x: string]: unknown; text: string; uri: string; mimeType?: string | undefined; } | { [x: string]: unknown; uri: string; blob: string; mimeType?: string | undefined; }'.
                        Type '{ uri: string; mimeType: "text/html" | "text/uri-list"; text?: string | undefined; blob?: string | undefined; }' is not assignable to type '{ [x: string]: unknown; uri: string; blob: string; mimeType?: string | undefined; }'.
                          Types of property 'blob' are incompatible.
                            Type 'string | undefined' is not assignable to type 'string'.
                              Type 'undefined' is not assignable to type 'string'.
  Overload 2 of 6, '(name: string, paramsSchema: ZodRawShape, annotations: { [x: string]: unknown; title?: string | undefined; readOnlyHint?: boolean | undefined; destructiveHint?: boolean | undefined; idempotentHint?: boolean | undefined; openWorldHint?: boolean | undefined; }, cb: (args: { ...; }, extra: RequestHandlerExtra<...>) => { ...; } | Promise<...>): RegisteredTool', gave the following error.
    Argument of type 'string' is not assignable to parameter of type 'ZodRawShape'.

[liady]

@aharvard good catch! Thanks.

[idosal]

Thanks @aharvard ! Super appreciated.

Please note that there's a lint error. We'll merge as soon as the workflow is green.

[liady]

@aharvard can you try wrapping the exhaustive check clause in parentheses - and check if it fixes the lint error?

Suggested change

	default:
	// Exhaustive check
	const exhaustiveCheck: never = options.delivery;
	throw new Error(`Invalid delivery type: ${exhaustiveCheck}`);
	default: {
	// Exhaustive check
	const exhaustiveCheck: never = options.delivery;
	throw new Error(`Invalid delivery type: ${exhaustiveCheck}`);
	}

[aharvard]

Ah, thanks for the heads up! I wrapped it with an IIFE, and that fixed it locally.

[idosal]

Merged. Thanks for the contribution @aharvard !