The mobile Piano Roll becomes a unified, keyboard-primary instrument surface
(wireframe Plate 04/08): a playable keyboard as the base, revealing a
Synthesia-style falling-notes roll above it when the pane is tall enough.
- Shared keyboard geometry (panes/keyboard_layout.rs): width-driven, pan-aware
pitch->x, so the roll's note columns stay aligned with the Virtual Piano keys.
Shared keyboard_octave + keyboard_pan_x in SharedPaneState.
- Piano Roll vertical mode (is_mobile): notes as columns falling toward an amber
now-line by the keys, tempo-map converted (beats->seconds) so onsets cross the
line exactly when they sound. Vertical drag scrubs the timeline; horizontal
drag smoothly scrolls the keys (snaps to nearest key on release). Long-press
creates a note (drag to size) or resizes an existing one; pan suppresses it.
The keyboard is embedded (reuses Virtual Piano render + MIDI); the standalone
VirtualPiano stack slot is removed. show_roll is driven by the snapped pane
size-class so the keyboard<->roll reveal lands on a stack snap point.
- Virtual Piano: renders via the shared layout on mobile, colors playback_notes
like pressed keys, gates note-on/glissando to presses that start on the keys
(never gating release), and hides QWERTY hints on mobile.
- Transport formats by document.timeline_mode (Measures->bar.beat.tick,
Frames->MM:SS:FF, Seconds->MM:SS.mmm) — per project type, like desktop.
- In-pane instrument header (name + Presets + REC). Recording is driven from the
app each frame (not the Timeline pane's render) so REC works regardless of
visible panes, and stopping playback stops recording.
- Compose/Record intent opens Timeline + instrument pane; mobile central panel is
full-bleed (no inner margin) so panes sit flush.
- phone-ui-sketches.html: inst-bar moved to the top of the music surface.
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