Sweep spatial profiles as surfaces, keep swept surfaces linked to expressions

A closed 3D polyline profile that does not lie in one plane sweeps a
surface with the reference's refusals. Swept surfaces made with an
Expression scale or twist follow the named parameters, and reference
surfaces linked through their associative action are picked up on open.
Saving keeps the associative actions the constraint graph does not
rebuild and stores each scope network through its own dictionary.
Kernel 23138fc, codec 64fe2a6.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/command.rs

@@ -2104,6 +2104,9 @@ pub enum CmdResult {
         mode: ExtrudeMode,
         options: SweepOptions,
         color: [f32; 4],
+        /// Scale and twist expressions entered with the Expression option;
+        /// a swept surface stays linked to them.
+        expressions: [Option<String>; 2],
     },
     /// Loft through ordered cross-sections, with optional guides or a path.
     LoftEntities {