In Settings → Integrations, install Apple Shortcuts. Copy the Granite URL and your action key.
In the Shortcuts app, create a shortcut and add Get Contents of URL with the Granite URL.
Set Method to
POST, add the headerAuthorizationwithBearerand your action key, and a JSON body:actionset tocapture, andcontentset to the Shortcut Input.Turn on Show in Share Sheet.
Now share a web page, a photo caption, or a text selection to the shortcut, ask Siri to run it, or add it as a widget. Whatever you send lands in your inbox note.