Reading https://mcpui.dev/guide/client/resource-renderer and looking through the source code I see that by default there's some hardcoded logic to determine how to treat the sandbox attribute of the iFrame.

I believe we have a use-case where we want the iframe to allow submitting a form within it and then passing the result of the form submission back to the parent via the dom once the form submission result is available.

This issue is a change to discuss the implementation.

I was thinking of two approaches, not sure which is favored. Assume that both would be backwards compatible and the same behavior as today would work out of the box, these are just overrides.

1. Allow specifying additional sandbox permissions via the react component

<UIResourceRenderer
  resource={mcpResource.resource}
  supportedContentTypes={['rawHtml']}
  onUIAction={handleUIAction}
  sandboxPermissions="allow-forms allow-scripts"
/>

2. Allow specifying additional sandbox permissions via the MCP response payload

{
  "type": "resource",
  "resource": {
     "uri": "ui://product/gid://shopify/Product/123123",
     "mimeType": "text/uri-list",
     "text": "https://cdn.shopify.com/storefront/product.component?store_domain=demostore.mock.shop&product_handle=hoodie"
     "sandboxPermissions": "allow-forms allow-scripts"
  }
}

The first feels a little more secure since it's the client that's specifying the control. On the latter you're trusting the server to provide the correct permissions. Maybe ultimately both are required with the client setting the baseline but for an initial implementation I'd lean towards just the client side.

Ref #30