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.

crates/sketch/src/link.rs

@@ -130,6 +130,10 @@ pub struct Link {
     /// Persistent model face identity, resolved by the document before geometry refresh.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub face_name: Option<String>,
+    /// Persistent model edge identity of an `Edge` source, resolved by the document before
+    /// geometry refresh. None: the edge is the one nearest the source's point.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub edge_name: Option<String>,
     /// Automatically projected borders owned by a durable sketch face attachment.
     #[serde(default, skip_serializing_if = "std::ops::Not::not")]
     pub auto_face: bool,
@@ -476,7 +480,7 @@ impl Sketch {
             return Err(SketchError::TooLarge);
         }
         let id = self.fresh("j")?;
-        self.links.push(Link { id: id.clone(), kind, source, face_name: None, auto_face: false, lost: false });
+        self.links.push(Link { id: id.clone(), kind, source, face_name: None, edge_name: None, auto_face: false, lost: false });
         self.build_link(&id, &lay)?;
         Ok(id)
     }

crates/sketch/src/wire.rs

@@ -196,7 +196,7 @@ impl Sketch {
         }
         let id = if geom.is_empty() {
             let id = self.fresh("j")?;
-            self.links.push(Link { id: id.clone(), kind, source, face_name: None, auto_face: false, lost: false });
+            self.links.push(Link { id: id.clone(), kind, source, face_name: None, edge_name: None, auto_face: false, lost: false });
             id
         } else {
             self.add_link(kind, source, geom)?