The Frame tool (K, its own toolbar slot after the Crop group) draws a
rectangular or elliptical frame; the options bar picks the shape, Shift
constrains to a square or circle and Alt draws from the centre. A frame
drawn over the selected pixel layer's content takes that layer in;
otherwise it is an empty frame.
Frames are built as Frame from Layers builds them: a group clipped by a
layer mask (rectangular or anti-aliased elliptical). The new engine
command layer.new.frame does it in one Session::edit, so one undo step.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
