Is there any supported mechanism in Safari Web Extensions (MV3) for capturing or logging network request data (like fetch, XHR, or webRequest) triggered by the web page?

In a Safari Web Extension using Manifest V3, how can a content script access an HTML file that is bundled with the extension (e.g., to inject it as an iframe)? Safari's CSP seem to prevent the use of browser.runtime.getURL() in the MAIN world — is there a recommended way to load such resources securely?