Tap the instrument name -> a modal to change Sound (cycle the GM voices), Beats (1-12),
Subdivision (1-8), Swing, and Mute, plus + Lane / Remove (1..MAXLANES). Beats/sub changes
regenerate the lane's default accents; sound/swing/mute keep the pattern. Reuses the
existing dirty + Save/Revert + .mpy machinery (edits to a built-in save a copy to
"My edits"). The modal redraws live as you adjust; tap Done or outside to close.
Verified in harness: editor opens (13 hit-zones), sound cycles, beats/sub regen steps,
swing/mute toggle, add/remove lanes, the edited track serializes + round-trips, Done
closes; modal renders cleanly. app.mpy builds (C/v6).
This completes the Phase-2 editing set (beats + lanes + Continue + built-in/user split).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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