CoreMIDI Automatic MIDI-CI Session interference handling

[hakaru]

Summary

macOS CoreMIDI (15.x Sequoia+) automatically initiates MIDI-CI sessions (Discovery Inquiry, PE GET) when a USB MIDI device is connected. This happens even if the application does not use MIDI-CI.

Problem

In a routing scenario (App connecting two devices), this leads to:

1. Duplicate Discovery/PE messages (from OS and App).
2. Hardware hangs (confirmed with KORG KeyStage) due to duplicate multi-chunk replies.
3. Observed 'Ghost' MUIDs (e.g., ).

Recommended Fix

• Implement MUID filtering/blacklist in to ignore messages from macOS CoreMIDI.
• Document known OS MUID patterns to help developers identify this interference.

Ref: Section 2.