Render: live objects in symbol art and opacity masks keep their evaluations between frames

The renderer placed symbol art that holds a blend, an envelope or a
repeat again for every instance in every frame. The live object in the
placed copy was a new node each time, and the renderer evaluated it
again. Symbol art that is itself a live object, an opacity mask whose
art is one, and a live object in a clip group in Outline view were
drawn from an uncached copy in every frame. At 1000 x 1000 pixels,
2,000 instances of a symbol holding an envelope took 126 ms a frame on
main, and the same 2,000 envelopes on the page took 30 ms.

The renderer now keeps the placed art of instances and inline graphics
when it holds blends, envelopes or repeats, and when the art is itself
a live object. It draws kept live art, opacity-mask art and Outline
view clip members that are live objects from the live cache, which
evaluates them again when the symbols, patterns, fonts or color
settings they show change. The 2,000 instances take 28 ms a frame,
with the same pixels.

Docs: docs/target-app-parity.md

docs/target-app-parity.md

@@ -966,6 +966,8 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
 
 - **Type with transparency or effects:** type at less than 100% opacity, in a blend mode other than Normal, or with raster effects such as a drop shadow keeps its glyph outlines between frames, as opaque type does, and is laid out again when it is edited or the fonts change. At 2880 × 1800 on 8 threads, a page of 1,000 type objects takes 13 ms a frame instead of 23 ms at 80% opacity, 31 ms instead of 41 ms in Multiply and 16 ms instead of 26 ms with a drop shadow, with the same pixels.
 
+- **Live objects in symbols and masks:** symbol instances and inline graphics whose symbol is a blend, an envelope, a repeat, an Intertwine object or a gradient mesh, or a group that holds one, draw the evaluation the renderer keeps for that object between frames, as the same object on the page does. So do opacity masks whose art is such an object, and such objects in clip groups in Outline view. The object is evaluated again when the symbols, patterns, fonts or color settings it shows change. Symbol art with effects of its own, or that holds a symbol instance, an image, a placed file, type with an inline graphic or a raster effect, is still placed and evaluated again in every frame. At 1000 × 1000 pixels, a page of 2,000 instances of a symbol that holds an envelope takes 28 ms a frame instead of 126 ms, with the same pixels.
+
 - **Type drawn as glyph outlines:** under a geometry effect, in EMF and WMF export, in DXF export when it is written as outlines, flattened with Convert All Text to Outlines, and inside an envelope, type keeps its underline and strikethrough, the weight and dashes of its character strokes when it is scaled, and the placement of its gradients and patterns, as the canvas draws it. A group's or layer's own fills and strokes also paint the underline and strikethrough of the type in it.
 
 - **Texture redraws (#1257):** Craquelure, Mosaic Tiles and Stained Glass compare squared distances when finding their nearest cells; rounding/tie boundaries use the original distance ordering. Brute-force candidate tests and three 1800×1500 viewport comparisons preserve the old pixels. A CMYK rectangle move at 190.07%/DPI 1.5 is reproducible with `cargo test -p vectorcraft-render texture_drag_perf -- --ignored --nocapture`; idle-machine Windows interaction is still unverified.