MIDI (and the MIDI clock) were started in onStart and stopped in onStop, so
turning the screen off — which drives the Activity to onStop — closed the MIDI
ports and dropped controller input. Move their lifecycle to onCreate/onDestroy so
input persists for the Activity's whole lifetime; onStop keeps only the project
autosave. The audio engine already runs a continuous output stream via the started
PlaybackService, which keeps the process alive (verified at PERSISTENT_SERVICE_ADJ
when backgrounded) to receive events with the screen off. USB MIDI needs no runtime
permission, so it works unconditionally.
Trade-off: the controller stays claimed by the app while backgrounded, and is
released only when the Activity is torn down (task removed / finishing).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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