- New crate lightcraft-slideshow (L1, no UI): SlideSettings (margins linked or
independent, guides, aspect preview, zoom to fill, stroke border, cast shadow,
backdrop colour, colour wash, background image; lengths relative to the slide's
shorter side; validated and clamped) and a CPU compose() used by playback, the
Settings preview and slideshow.preview.
- Engine: slideshow.layout (partial merge, saved in prefs.json) and
slideshow.preview {id?, width?, height?, path?} (PNG to path or base64);
RenderJob::with_slide composes on the render worker; the background photo is
rendered once and shared.
- Playback: with a non-default layout each slide is the composed screen-sized
slide, prepared ahead like before; the default layout plays as before.
- Settings > Slideshow: Layout, Options and Backdrop sections and a debounced
live preview of the active photo's slide (with margin guides).
- Tests: composer geometry/pixels/hostile input, command get/set/persist/preview,
headless playback of a composed slide and of the default layout.