Littledata's app tracks your checkout and orders server-side. To link these events on Shopify with the user's pre-checkout visit on a headless site you just need a few extra setup steps.
See it in action: https://headlessdemo.littledata.io
Including ?segment=true in the URL switches to the guide for our Segment app, or you can use the button in the header to switch platform
Nacelle has developed an NPM package to automate steps 4 and 5.
Adding sendClientId=false to the URL parameters will cause the private app NOT to add cart attributes, and as a result the order will come through with no note_attributes field.