fix: a projected edge stays the edge that was picked when its body changes (#730)

A sketch's link to a projected edge now keeps the edge's persistent name and finds it by that name when the body changes, instead of taking whichever edge ends up nearest its point.

docs/book/src/guide/files.md

@@ -58,7 +58,7 @@ is available. Missing or incompatible pictures use the usual thumbnail generatio
 The default `cache: false` omits the portable thumbnail too.
 The repository's `docs/design-container.md` describes limits and encoding details.
 
-Current designs use format 17, including face anchors on a piece of a face by its own name, sheet metal rims and bend ends, bend edges for Convert to Sheet Metal, physical materials defined in the design, the font of sketch text, sheet metal corner relief shapes, sketch face anchors on cylinder caps, sketch axis
+Current designs use format 17, including face anchors on a piece of a face by its own name, sheet metal rims and bend ends, bend edges for Convert to Sheet Metal, the names of projected edges, physical materials defined in the design, the font of sketch text, sheet metal corner relief shapes, sketch face anchors on cylinder caps, sketch axis
 links, persistent
 names from exact face history, exact planar shell-face anchors, persistent analytic offset boundary roles and
 association profile references, durable sketch face anchors, periodic fit splines and versioned

docs/book/src/guide/sketching.md

@@ -59,6 +59,8 @@ design unchanged. Projected geometry remains protected from ordinary dragging.
 
 **Project** (P) and **Intersect** bring model edges into the sketch as linked geometry that
 follows later changes. Sketching on a face projects its edges automatically.
+A projected edge stays the edge that was picked, wherever a later change moves it; when that
+edge no longer exists, the projection keeps its last shape and the sketch says it was lost.
 For Project, select visible source curves or points from another sketch, model edges,
 faces, vertices or bodies, or axes and planes, then press P. The entire supported selection
 is projected in one undo step. A rejected projection keeps the selection for correction;