feat: preserve body history and placed modelling workflows

Record ownership transfers in the timeline so earlier Join/Cut membership,
world placement, machining data and styles survive component moves, edits,
independent copying, undo and reopening. Preserve pending positions in history
snapshots and keep constructor transfers ordered during feature redefinition.

Retain shallow sheet pockets and exact planar intersection islands through
unfold/refold, with depth-aware flat previews and DXF export. Store explicit
3D wire coordinate spaces and migrate known legacy provenance without moving
saved points or analytic fits.

Infer unique eligible cylindrical Emboss targets, align Revolve manipulators
with actual extent geometry, and discard obsolete preview errors after input
correction. Certify constructed and immutable imported face styles using exact
source metadata while preserving legacy face names. Upgrade designs to format10
with bounded validation and geometry-preserving legacy migration.

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

@@ -38,3 +38,18 @@ Cuts can leave separate material pieces, including the centre of a ring cut. The
 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.
+
+Parallel, untapered extrude cuts also preserve shallow pockets through Unfold / Refold.
+The pocket floor and side walls remain solid geometry; overlapping cuts from opposite sides
+become a through hole wherever they remove the whole thickness. Flat-pattern JSON lists
+`pockets` with their side, depth and bottom/top thickness coordinates in millimetres.
+DXF pocket boundaries use `POCKET_BOTTOM_Z…_TO_…_MM`, `POCKET_TOP_Z…_TO_…_MM`, or
+`POCKET_INTERNAL_Z…_TO_…_MM` layers. These are machining operations, so do not treat every
+pocket layer as a through-cut contour when importing the drawing into a CAM tool.
+
+Extrude Intersect on a straight base or an unfolded sheet retains the exact planar material,
+including interior holes and detached islands. A completely empty intersection removes the
+sheet and its metadata together. Pocket profiles can move with planar panels when forming,
+but a pocket crossing a bend zone cannot yet be refolded. Machining folded bend material,
+tapered sheet cuts and other unsupported 3D sheet Cut/Intersect operations report an error before changing
+the design; they cannot silently restore removed material during a later sheet rebuild.