Fix Universal Control support

[evoleinik]

Summary

Mac Mouse Fix doesn't work on the receiving Mac when using Universal Control (or other virtual input sources like screen sharing, VMs). This PR fixes three root causes:

1. Scroll events filtered out — Scroll.m:eventTapCallback filters scrollPhase != 0, which discards ALL Universal Control scroll events. UC relays trackpad gestures that carry phase data real scroll wheels never have. Fix: skip the scrollPhase filter when CGEventGetSendingDevice returns NULL (virtual input source).

2. Button events pass through unprocessed — ButtonInputReceiver.m returns immediately when sendingDev is NULL, so button remapping never happens for UC events. The NO_FILTER macro that would handle this was never defined despite comments saying it should be on ("We're leaving NO_FILTER on for now, because I can't really think of a good reason to filter"). Fix: always use [Device strangeDevice] for unknown sources.

3. Event taps disabled without physical device — All someDeviceHas* guards in SwitchMaster.swift prevent taps from enabling when no IOHIDDevice is attached. Fix: remove these guards. Event taps that receive no events consume zero CPU.

Additionally:

• DeviceManager.m: default maxButtonNumberAmongDevices to 5 when no physical devices are attached
• Scroll.m: remove assert(sendingDev != NULL) that crashes on UC events in pre-release builds

Files changed

File	Change
Helper/Core/Scroll/Scroll.m	Skip scrollPhase filter for virtual input; remove sendingDev assert
Helper/Core/Buttons/ButtonInputReceiver.m	Use strangeDevice for NULL device instead of pass-through
Helper/Core/Coordinate/SwitchMaster.swift	Remove all someDeviceHas* guards from toggle functions
Shared/Devices/DeviceManager.m	Default to 5 buttons when no devices attached

Testing

• Compiles clean on Xcode 26.3 / macOS 26.2 SDK (only pre-existing deprecation warnings)
• Could not test at runtime due to code signing requirements (no development certificate for com.nuebling.mac-mouse-fix)

Issues

Fixes #277, #365, #526, #554, #803, #1235

🤖 Generated with Claude Code

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com

[evoleinik]

@noah-nuebling Hi Noah! I hope it's OK that I sent an AI-generated PR. Bascially, the point is to make MMF work on the second mac, connected via Universal Control. I can't properly test it on my local mac.

[evoleinik]

Hey Noah, gentle bump on this. 👋

I wasn't able to test at runtime because building without your signing identity means the Helper can't register as a login agent (SMAppService requires a proper code signature with keychain entitlements).

Is there a recommended workflow for contributors to test locally? E.g. a way to bypass the login item registration for dev builds, or should I just sign up for a free Apple Developer account and use automatic signing with my own team ID?

Happy to adjust anything in the PR if you have feedback on the approach.