fix(render): keep an SVG inside the bounds it was given

[samyfodil]

An icon painted over the chrome around it. A 16x16 gear in a tab bar's trailing cluster drew a block from its own origin to the corner of the window:

SceneCanvas.RenderSVG positions the document with a transform built from the bounds it is handed, but never constrains it to them. Anything the document draws past its own viewBox lands on whatever surrounds the icon.

That is not a malformed document. An SVG may draw anywhere and every spec-following renderer clips to the viewport; icon sets rely on it, since a stroke centred on the viewBox edge puts half its width outside. So the usual case is a bleed of a pixel or two — invisible wherever another widget paints afterwards and covers it. It only surfaces on the last icon in a row, or one against the edge of a window, where nothing paints over the spill.

Where it came from

The switch to vector re-emission in #200. The previous path rasterised the document into a bitmap sized from those same bounds, so the bounds were enforced by construction — nothing could escape a raster that size. Emitting geometry straight into the scene removed that guarantee and nothing replaced it. Bisected: clean at cd1f292, reproducing at 707bbf3, same gg version either side.

The change

Two, both making RenderSVG behave like every other draw method on the canvas:

• Push a clip of the given bounds around the emission, bounding the document the way the raster used to.
• Honour the current clip. Every sibling returns early when isVisible is false; RenderSVG was the one that did not, so an icon with no pixels on screen still emitted its whole document.

Tests

Both covered, with a document that deliberately draws 4x its viewBox — the visible version of the stroke case. Scene.Bounds() is the union of the shapes and does not narrow for a clip, so the test inspects the emitted commands. Both fail on main and pass here; full suite green (61 packages).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[kolkov]

Validated: SVG spec requires viewport clipping (overflow defaults to hidden, W3C REC-SVG11 section 7.9). Skia's pattern is caller-side clip — our SceneCanvas is the caller. PushClip with rect shape has near-zero overhead (2 tags). The isVisible early-out is an additional win that was missing only from RenderSVG.