feat: preserve modeling intent across sketches, assemblies, and fabrication

Persist typed sketch dimensions and bounded ordered configuration rules in format 8. Use exact occurrence paths and source identity for editing, movement, appearance, and mass. Preserve sheet material regions through cutting, folding, and exact DXF export; retain nested cavities and material islands.

Validation: cargo xtask ci passed, including 368 engine tests, 178 UI tests, 68 UI scenarios, 136 kernel tests, and the 10-crate wasm check. Actual preview workflows and legacy format-7 origin-corner reopening were inspected.

docs/book/src/guide/sheet-metal.md

@@ -28,3 +28,13 @@ consume an undo step.
 
 DXF cutout geometry preserves lines, circles and circular arcs; other curves are sampled
 adaptively. The `OUTLINE`, `BEND_UP` and `BEND_DOWN` layers separate cuts from bend centres.
+
+Base-flange profiles keep their interior holes. Through cuts that cross a sheet edge become
+notches in the flat outline; overlapping and repeated cuts remove their combined area once.
+The flat preview, DXF and unfolded solid use the same material boundaries. Lines and circular
+arcs remain exact; other profile curves use a 0.001 mm chord tolerance.
+
+Cuts can leave separate material pieces, including the centre of a ring cut. These pieces
+remain one logical sheet group through Unfold / Refold and export as separate flat outlines.
+Large profiles that exceed the geometry processing budget report an error instead of
+exporting a partial outline.