A behaviour suite for export and inspect, written from public documentation of design tools'
export settings and developer handoff modes (`crates/engine/src/export_behaviour_tests.rs`,
`crates/engine/src/inspect_behaviour_tests.rs`: 19 tests, 139 table rows and asserts, each with a
one-line derivation; rows where the docs are silent say so and pin today's behaviour). 47 cases
failed on `main`; this PR fixes them in shared code.
**Fixes**
- Export bounds are what a layer paints (`Document::world_render_bounds`, used by every export):
a drop shadow adds room only in the direction it falls (it was a symmetric margin of blur +
largest offset on every side); strokes on rectangles, frames and ellipses reach their real width
(the mitre factor made a centre stroke of 4 add 8 a side); hidden children take no room; a mask
group exports the mask's area.
- Slices export everything visible in their area (they exported an empty image).
- Slashes in layer names export into folders (`icons/close` → `icons/close.png`, folders created;
`.` and `..` segments dropped).
- Copy as PNG copies the whole selection (only the first layer was copied), now from shared code
(`cmd::file::copy_png`).
- Inspect positions are measured from the frame around a layer; groups aren't frames.
**Added (documented options that were missing)**
- Export settings: contents only (off draws every layer showing in the area) and include bounding
box (the layer's own box); SVG: outline text (off writes `<text>` with a `<tspan>` per line),
id attributes (unique), simplified strokes (stroke attributes for centred strokes, and for inside
and outside strokes on boxes and ellipses). Stored per export setting, taken by `file.export`,
`export.add` / `export.update`, `file.exportLayers` and MCP `export`; a "…" popover on each row of
the Export section.
- Inspect: colour formats hex / RGB / CSS / HSL / HSB (`inspect.properties {colorFormat}`, a Color
format dropdown), a Blend row, CSS in rem (`inspect.code {unit, rootFontSize}`, px/rem dropdown),
CSS for rotation, blend modes, gradient directions and kinds (linear angle, radial, conic), text
alignment, case and decoration; icons and images in the asset list (`kind`), exported with
`file.exportLayers {assets: true}`.
**A paint and effects behaviour suite written from the public documentation, and fixes for every divergence it found.** Each documented rule (fill stacking and opacity, paint vs layer opacity, every blend mode per paint and per layer, pass-through and Normal containers, the four gradient kinds and their handles, stops, image scale modes, rotation and adjustments, the colour models and hex entry, the document colour profile, drop and inner shadows, showing shadows behind transparent areas, layer and background blurs, effects on groups, effect order, what exports include) is a table-driven case with a one-line derivation; where the documentation is silent the case says so and pins today's behaviour. Scenes are small and synthetic; pixel cases use tolerances (blurs are checked against the normal distribution with sigma = radius / 2).
**Fixes (13 render cases and 8 command/export cases fail on the old code)**
- **Pass-through and Normal containers**: a group or frame set to Normal now blends its children among themselves first (it never isolated), and a **clipping frame no longer isolates** its children: they were drawn on a fresh layer, so a Multiply child inside a frame (frames clip by default) met neither the frame's fill nor what is behind it. The clipped layer now starts as a copy of what lies under it and goes back in its place through the clip (a memcpy for rectangular clips, so no slower); backdrop effects see the right composite, also for a clipping frame inside a faded group. Same in exports: SVG gives Normal groups `isolation:isolate` and puts a clipping frame's clip on what blends instead of a clipped `<g>` (a clipped group is a stacking context, which isolates); PDF wraps Normal groups in an isolated group (`Node::isolates_children`, shared).
- **Plus darker** (linear burn) is drawn by its formula on the canvas and in pixel exports for paints, layers, shadows and noise (it was multiply); tiny-skia lacks the mode, so `fx::plus_darker` composites it and `paint::composite` routes every layer, shadow and noise composite through it.
- **Shadows hidden behind the layer**: a drop shadow that doesn't show behind transparent areas is now hidden behind what the layer covers, translucent and 0% fills included (it was cut out by the layer's alpha, so it showed through a 50% fill anyway); groups and layers whose pixels a layer blur or texture moves still hide it behind their pixels. One `shadow::Caster::new` serves the canvas, PNG and the PDF's shadow rasters. **SVG** never cut shadows out: its filters now composite them `out` of an image of the layer's outline (or `SourceAlpha` for groups), and the filter region reaches as far as the effects (a fixed 200% box cut off a small layer's long shadow).
- **Fill images cover the box to its edges**: an upscaled Fill (or covering Crop) image faded to transparent over a source pixel at the box's edge.
- **"Normal" meant pass-through** when named: `BlendMode::from_name("normal")` found pass-through first (its CSS keyword is also `normal`), so `node.set {blend: "normal"}` and the blend menu's Normal set pass-through. Labels now win, and the menu sends labels.
**Added**
- A blend mode menu for each paint in the colour picker (no pass-through for paints), sharing `right::blend_menu` with the Design panel's layer menu; strings already translated.
- Inspect (`node.get`, MCP) reports a solid paint's `blend` when it isn't normal.
