Engine (scripts, the control channel and agents can drive it):
- `select.float {"dx","dy"}`: cuts the selected pixels of the active layer
into a floating piece the first time, then moves it by whole pixels.
The document is unchanged while it floats (`DocState::floating`);
`float_cmds::displayed` gives the document with the piece at its offset.
- `select.drop`: drops the piece into its layer and moves the selection
with it, one history step ("Move Selected Pixels").
- Any other command drops a floating piece first (a hook at the top of
dispatch, so it lands where it was shown); Undo puts it back instead.
- The layer is split once, only inside the selection, and the piece is
cropped to it: placing it costs the piece, not the layer (6000×4000
layer, 500×400 piece: 18 ms to cut, under 5 ms per move).
Canvas (Marquee / Lasso):
- A drag inside the ants moves the outline (`select.transformSelection`);
a click inside without moving deselects; ⇧ / ⌥ drags still draw.
- ⌘-drag floats the selected pixels and shows them at the pointer live;
plain drags on the piece move it again; a press elsewhere drops it.
- A move cursor over the ants; the ants follow the dragged / floating piece.
Co-authored-by: Jason Short <3344856+jason4short@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
