diff --git a/crates/cord-gui/src/app.rs b/crates/cord-gui/src/app.rs
index 1471312..745c015 100644
--- a/crates/cord-gui/src/app.rs
+++ b/crates/cord-gui/src/app.rs
@@ -6,7 +6,7 @@ use iced::widget::{
 use iced::{Background, Border, Color, Element, Fill, Length, Padding, Shadow, Subscription};
 use iced::{mouse, keyboard, window, Point, Vector};
 use std::path::PathBuf;
-use std::sync::Arc;
+use std::sync::{Arc, mpsc};
 use std::time::Duration;
 
 use cord_expr::{classify, classify_from, expr_to_sdf, parse_expr, parse_expr_scene, ExprInfo};
@@ -39,6 +39,7 @@ pub struct App {
     cursor_line: usize,
     line_eval_text: Option<String>,
     mesh_path: Option<PathBuf>,
+    mesh_import_rx: Option<mpsc::Receiver<Result<(String, PathBuf), String>>>,
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -80,6 +81,7 @@ pub enum Message {
     RenderPlots,
     RenderAll,
     DecomposeMesh,
+    MeshImportComplete(Result<(String, PathBuf), String>),
     Tick,
 }
 
@@ -147,6 +149,7 @@ impl App {
             cursor_line: 0,
             line_eval_text: None,
             mesh_path: None,
+            mesh_import_rx: None,
         };
         app.reparse();
 
@@ -328,12 +331,39 @@ impl App {
                 }
             }
             Message::DecomposeMesh => self.decompose_mesh(),
+            Message::MeshImportComplete(result) => {
+                match result {
+                    Ok((source, path)) => {
+                        self.source = text_editor::Content::with_text(&source);
+                        self.undo_stack = vec![source];
+                        self.redo_stack.clear();
+                        self.mesh_path = Some(path.clone());
+                        self.current_path = Some(path.clone());
+                        self.dirty = false;
+                        self.detect_mode();
+                        self.reparse();
+                        self.update_markdown();
+                        self.push_recent(&path);
+                        self.status = Some(format!("opened: {}", path.display()));
+                    }
+                    Err(e) => {
+                        self.status = Some(format!("mesh import error: {e}"));
+                    }
+                }
+            }
             Message::Tick => {
                 if !self.menu_ready {
                     setup_native_menu();
                     self.menu_ready = true;
                 }
                 self.poll_menu_events();
+                if let Some(rx) = &self.mesh_import_rx {
+                    if let Ok(result) = rx.try_recv() {
+                        self.mesh_import_rx = None;
+                        self.update(Message::MeshImportComplete(result));
+                        return;
+                    }
+                }
                 let new_line = self.source.cursor().position.line;
                 if new_line != self.cursor_line {
                     self.cursor_line = new_line;
@@ -637,7 +667,18 @@ impl App {
             .unwrap_or("")
             .to_lowercase();
 
-        let is_mesh = matches!(ext.as_str(), "obj" | "stl" | "3mf");
+        if matches!(ext.as_str(), "obj" | "stl" | "3mf") {
+            self.status = Some(format!("decomposing mesh: {}…", path.display()));
+            let (tx, rx) = mpsc::channel();
+            let path_owned = path.to_path_buf();
+            std::thread::spawn(move || {
+                let result = import_mesh(&path_owned)
+                    .map(|source| (source, path_owned));
+                let _ = tx.send(result);
+            });
+            self.mesh_import_rx = Some(rx);
+            return;
+        }
 
         let result = match ext.as_str() {
             "zcd" => load_zcd(path),
@@ -645,9 +686,6 @@ impl App {
             "cord" | "bin" => {
                 Err("binary format (.cord) — no source to edit".into())
             }
-            "obj" | "stl" | "3mf" => {
-                import_mesh(path)
-            }
             "step" | "stp" => {
                 Err(format!("import for .{ext} not yet implemented"))
             }
@@ -660,7 +698,7 @@ impl App {
                 self.undo_stack = vec![source];
                 self.redo_stack.clear();
                 self.current_path = Some(path.to_path_buf());
-                self.mesh_path = if is_mesh { Some(path.to_path_buf()) } else { None };
+                self.mesh_path = None;
                 self.dirty = false;
                 self.detect_mode();
                 self.reparse();