Merge remote-tracking branch 'origin/main' into feat/sketch-tools-return-ids

# Conflicts:
#	crates/engine/src/cmd/mod.rs
#	crates/engine/src/cmd/sketch.rs
#	crates/engine/src/cmd/sketch_create.rs
#	crates/engine/src/cmd/sketch_modify.rs
#	crates/engine/src/lib.rs
#	docs/book/src/guide/sketching.md

docs/book/src/guide/sketching.md

@@ -20,6 +20,43 @@ ids of what it added (`created: {points, curves, constraints, dimensions}`). Ids
 never reused within a sketch, even after a delete, so a script can dimension or constrain the new
 geometry right away.
 
+Extend finds intersections with exact ellipses, rational conics and spline spans. It keeps the
+original line or circular support and extends only beyond the selected endpoint; conflicting
+constraints or an ambiguous overlap leave the sketch unchanged.
+
+Offsets of smooth ellipses, conics and splines follow their source after dimension changes,
+dragging and reopening a design. Their stored cubic spline has a whole-span normal-distance
+error bound of 0.002 mm. Singular tangents, curvature cusps, possible self-intersections and
+excessive subdivisions are refused. Offset these curves individually: mixed chain junctions
+currently require separate geometry. `sketch.offset.break` releases an offset for independent
+editing, and undo restores its association. Older independently sampled offsets remain independent.
+Smooth open and newly created smooth closed offsets can be offset again, including bounded
+refinement after a source edit. New closed outputs use a periodic cubic fit with continuous
+tangent and curvature at the seam. Break Offset Association preserves that interpolation,
+and its closing point remains joined when dragged. Deleting an output also removes its
+unused private fit points; deleting a source with a retained dependent is refused.
+
+For explicit closed fit splines, `sketch.spline.fit_point` accepts `periodic: true` and at
+least three distinct cyclic samples. It closes the loop automatically. Existing calls and
+older saved closed splines retain natural interpolation; older associative closed offsets
+also retain their saved natural fit. A legacy seam without a unique normal still refuses
+another offset. Periodic intent is stored on each curve and survives save, reopen and Break.
+While drawing a fit spline, click its starting point after three distinct samples to close
+it smoothly. Right-click finishes an ordinary natural fit. Offset accepts both ellipse
+handles and dense fitted curves; the second click sets the side and distance from the curve.
+
+Enable **3D Sketch** in the Sketch Palette to draw lines, fit splines and points off the plane.
+New 3D geometry follows its sketch's component placement, including the selected occurrence
+and pending position changes. Click a drawn fit point to show its move triad; its arrows move
+along world X, Y and Z. Scripts also supply world coordinates to `sketch.line3d`,
+`sketch.spline3d`, `sketch.point3d` and `sketch.move3d`. Activate the desired occurrence before
+editing an explicit sketch belonging to a component with multiple placements.
+
+Older drawn or detached 3D wires keep their saved world positions. Included and surface-linked
+wires with an explicit component marker keep that meaning after the link is broken. Old files
+whose links became lost after an incorrectly scoped cross-component refresh may require a
+fresh link once the source is available; their stored point values are preserved on opening.
+
 ## Constraints and dimensions
 
 The solver is SolveCraft's own (damped Gauss–Newton with degree-of-freedom analysis). Constraints: