I got the ACE Pro working on the U1.

Yes, I know someone else posted a video of this recently, but their approach required major surgery on the stock U1 Klipper installation, and the part where they instructed users to enable debug mode on Paxx firmware didn't sit right with me. That's not something you want to do if you're not a developer.

So I set out to do this the proper way: no modifications to the base Klipper install. Instead, I cloned it, patched the copy, and ran it in parallel using Klipper Router: a JSON-RPC bridge that lets multiple Klippy instances communicate by publishing and subscribing to events, or by directly proxying commands between instances through the router.

When the "stage lane" macro runs, it pushes filament approximately 2200mm from the ACE to just before the toolhead. Before doing so, it disables auto-feed for that feeder on the U1 to avoid conflicts.

Next, the load assist macro enables the ACE's feed assist mode, which applies constant pressure to advance the filament while backing off if it senses resistance, effectively inching it into the extruder. Once it's seated, auto-feed is re-enabled and the U1's autoload sequence can be initiated, provided the filament type has already been set.

Klipper Router events and macro hooks keep the ACE's feed assist active for whichever toolhead is currently picked, and disable it automatically when all toolheads are parked, though the ACE will also disengage on its own if there's no downstream path to push filament into.

To test a build of Paxx12 extended firmware with the ACE Pro support added, download from this action workflow run:
https://github.com/justinh-rahb/SnapmakerU1-Extended-Firmware/actions/runs/23039952135