- Pinch and Cmd+scroll zoom the timeline around the pointer. egui 0.36 turns
both into zoom_delta, so the old Cmd+scroll branch never ran; Shift+wheel
pans sideways again for the same reason.
- Two-finger panning keeps the sub-sample remainder, so slow motion still
moves at the closest zoom; the scrollbar drag pans the same way (its range
now takes in the view, so the thumb stays in the bar), and the rulers pan
too. Panning stays open-ended to the right, as before.
- A swipe keeps to the axis it starts along, so panning doesn't drift between
tracks and scrolling doesn't drift in time. The larger share of its first
6 points decides until egui reports the scroll over: the fingers lift, or
150 ms pass without wheel events.
- The MIDI editor scrolls by the point instead of rounding each frame's delta
to whole rows (slow swipes did nothing), and its range fits the panel
(pitch 0 could not be reached; a taller panel showed blank rows).
- Zoom and scroll write through `Engine::zoom_mut` (`view` commands): no
playback resync (a session copy sent to the audio thread every frame), no
copy of the whole session per frame, no journal entry per frame, and no
end to an undo gesture (scrolling during an automation pass made each
write its own undo step). New `view.zoom_by {factor, x?}`;
`view.scroll` saturates; Fill Window and Zoom to Selection stay within the
zoom range (zooming out after them on a long session zoomed in).
- Control channel: `ui.scroll` (trackpad swipe or wheel notches) and
`ui.zoom` (pinch); `session.inspect` reports zoom.
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