Phase 7: Add MIDI clips, instrument and piano roll

docs/GUI.md

@@ -124,7 +124,7 @@ A ruler click seeks while stopped (or positions the cursor when disconnected).
 The 100 ms GUI refresh converts the backend's actual sample counter to ticks;
 it never integrates wall-clock time. Play resumes and Stop pauses. Reconnect,
 New and Open reset position. Add region creates silent metadata; imported WAV clips play through the
-audio source node (Phase 6 below). MIDI content is not implemented. The C model
+audio source node (Phase 6 below). MIDI clips and notes are described below. The C model
 supports a constant tempo; a tempo map and scheduler are future work.
 
 Tests cover C-model/persistence boundaries, GUI move/trim gestures and zoom,
@@ -155,3 +155,14 @@ See AUDIO_FILES.md for supported WAV formats, memory limits, musical placement,
 recording overflow/partial-take recovery, external asset portability and the
 software-only acceptance tests. Waveform drawing, input monitoring, recording
 latency compensation and per-track mixing are not implemented.
+
+## Phase 7 piano roll
+
+Add MIDI clip creates a one-bar clip on the selected/first existing track at the
+cursor. Select it and choose Piano roll (View/Piano roll, Ctrl+4). Click to draw,
+drag a body to move pitch/time, drag its right edge to resize, and right-click
+or Delete to remove. Notes use source ticks with 1/16 snapping; trimmed source
+content is retained. Edits stop transport and are blocked during audio recording.
+Panic/F9 silences held notes; Record continues to mean WAV audio capture.
+Modular Graph offers Add instrument for explicit routing. Status includes MIDI
+drops. See MIDI.md for voice limits, unsupported messages and live input routing.