Point clouds: drawn from their scans, placed, cropped and attached as the reference does

Scans (.rcs) and projects (.rcp) are read and their points drawn as
screen-sized dots, coloured by the cloud's stylization. The cloud's
placement carries its scale and rotation; its extents and crops stay in
the scan's coordinates. A missing scan shows the extents with the saved
path. -POINTCLOUDATTACH / POINTCLOUDATTACH, POINTCLOUDCROP and the
POINTCLOUD* settings follow the reference's prompts and messages, the
Properties list is the reference's, and a locked cloud is left alone by
edits.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/command.rs

@@ -1572,6 +1572,13 @@ pub enum CmdResult {
     OpenPdfImportSettings,
     /// Import a page of a file (PDFIMPORT File); ends the command.
     PdfImportFile(crate::modules::insert::pdf_import::PdfFileImport),
+    /// Attach a point cloud: the host creates or reuses its definition,
+    /// commits the cloud in one undo step, then ends the command. The
+    /// message is the last prompt's echo.
+    AttachPointCloud {
+        placement: crate::modules::insert::pc_attach::PointCloudPlacement,
+        message: String,
+    },
     /// Attach PDF pages: each page's underlay with its file (as stored) and
     /// page; the host creates or reuses the definitions and commits them all
     /// in one undo step, then ends the command.
@@ -2843,6 +2850,12 @@ pub trait CadCommand: Send {
         false
     }
 
+    /// The command moves, turns or resizes what it gathers: the host drops
+    /// locked point clouds from each completed selection and says so.
+    fn selection_drops_locked_point_clouds(&self) -> bool {
+        false
+    }
+
     /// Before each input the host says which block references carry a clip
     /// boundary.
     fn inject_clipped(&mut self, _clipped: &dyn Fn(Handle) -> bool) {}