Sketch: associative, editable sketch patterns (#1103)

Rectangular and circular sketch patterns stay linked to their source: editing the pattern's count, spacing or the source geometry updates the copies, and the copies keep their point and radius relations. Patterns are saved under format 20; older designs keep their independent copies.

crates/mcp/src/lib.rs

@@ -53,7 +53,9 @@ pub fn agent_scope_with(recovery: Option<PathBuf>, allowed: impl IntoIterator<It
 pub fn scratch_dir() -> Option<PathBuf> {
     static DIR: std::sync::OnceLock<Option<PathBuf>> = std::sync::OnceLock::new();
     DIR.get_or_init(|| {
-        let mut b = std::fs::DirBuilder::new();
+        let b = std::fs::DirBuilder::new();
+        #[cfg(unix)]
+        let mut b = b;
         #[cfg(unix)]
         std::os::unix::fs::DirBuilderExt::mode(&mut b, 0o700);
         let seed = std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH).map(|d| d.subsec_nanos()).unwrap_or(0);