In some applications, a Safari Web Extension must receive a Native Message and process it in the background, without activating Safari. For example, assuming that Safari Web Extensions will soon support the browser.bookmarks API - https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/bookmarks, when a bookmarks syncing application needs to push a new bookmark from a source of truth into Safari's bookmarks, it will send a Native Message to the extension, and this may happen when Safari is not the active macOS application, for example if the user is writing email in Mail. I am modifying Apple's Sea Creator - https://developer.apple.com/documentation/safariservices/safari_web_extensions/developing_a_safari_web_extension sample code to establish a proof of concept for such an application. So far, pretty good. I am able to send over 150 MB of data – far more than will be needed – from the app, to the extension's background.js script, and vice versa. However, it seems when Safari receives the m