diff --git a/crates/cord-gui/src/app.rs b/crates/cord-gui/src/app.rs
index 0905eef..1fc917c 100644
--- a/crates/cord-gui/src/app.rs
+++ b/crates/cord-gui/src/app.rs
@@ -429,17 +429,17 @@ impl App {
         {
             match ext.to_lowercase().as_str() {
                 "scad" => { self.mode = InputMode::Scad; return; }
-                "crd" | "obj" | "stl" | "3mf" => { self.mode = InputMode::Expr; return; }
+                "crd" | "zcd" | "obj" | "stl" | "3mf" => { self.mode = InputMode::Expr; return; }
                 _ => {}
             }
         }
         let s = self.source.text();
         let s = s.trim();
-        if s.contains('{') || s.starts_with("module ")
-            || s.starts_with("for ") || s.starts_with("if ")
+        let has_scad_blocks = s.contains('{') && s.contains(';');
+        let has_scad_keywords = s.starts_with("module ")
             || s.starts_with("difference") || s.starts_with("union")
-            || s.starts_with("intersection")
-        {
+            || s.starts_with("intersection");
+        if has_scad_keywords || (has_scad_blocks && !s.starts_with("let ") && !s.starts_with("sch ") && !s.starts_with("//")) {
             self.mode = InputMode::Scad;
         } else {
             self.mode = InputMode::Expr;
@@ -576,7 +576,13 @@ impl App {
         self.mode = InputMode::Expr;
         self.info = None;
         self.error = None;
+        self.scene_objects.clear();
+        self.selected_object = None;
+        self.needs_cast = false;
+        self.needs_plot = false;
         self.md_items.clear();
+        self.viewport.set_graph(&default_sphere_graph());
+        self.viewport.set_bounds(2.0);
         self.status = Some("new file".into());
     }
 
@@ -2295,4 +2301,78 @@ mod tests {
         let graph = cord_expr::resolve_scene(scene);
         assert!(evaluate(&graph, 1.0, 2.0, 0.0) < 0.0);
     }
+
+    fn sim_reparse(src: &str) -> cord_trig::TrigGraph {
+        use cord_expr::{classify_from, expr_to_sdf};
+        let src = src.trim();
+        let scene = parse_expr_scene(src).expect("parse failed");
+        let mut graph = scene.graph;
+        let mut sdf_roots: Vec<cord_trig::ir::NodeId> = Vec::new();
+
+        let render_objects: Vec<_> = if scene.cast_all {
+            scene.all_vars.clone()
+        } else if !scene.casts.is_empty() {
+            scene.casts.clone()
+        } else {
+            Vec::new()
+        };
+        for &(_, id) in &render_objects {
+            sdf_roots.push(id);
+        }
+
+        let mut plot_nodes: Vec<cord_trig::ir::NodeId> = if scene.plot_all {
+            let mut nodes: Vec<_> = scene.all_vars.iter().map(|(_, id)| *id).collect();
+            nodes.extend(&scene.bare_exprs);
+            nodes
+        } else {
+            Vec::new()
+        };
+        plot_nodes.extend(&scene.plots);
+        for &node_id in &plot_nodes {
+            let info = classify_from(&graph, node_id);
+            let sdf = expr_to_sdf(&mut graph, node_id, info.dimensions, 0.05, 10.0);
+            sdf_roots.push(sdf);
+        }
+
+        if sdf_roots.len() >= 2 {
+            let mut root = sdf_roots[0];
+            for &node in &sdf_roots[1..] {
+                root = graph.push(cord_trig::TrigOp::Min(root, node));
+            }
+            graph.set_output(root);
+        } else if sdf_roots.len() == 1 {
+            graph.set_output(sdf_roots[0]);
+        } else {
+            let empty = graph.push(cord_trig::TrigOp::Const(1e10));
+            graph.set_output(empty);
+        }
+
+        graph
+    }
+
+    #[test]
+    fn open_file_produces_different_wgsl() {
+        let default_src = "let s = sphere(3)\ncast()";
+        let shell_src = std::fs::read_to_string(
+            concat!(env!("CARGO_MANIFEST_DIR"), "/../../examples/shell.crd")
+        ).expect("can't read shell.crd");
+        let bolt_src = std::fs::read_to_string(
+            concat!(env!("CARGO_MANIFEST_DIR"), "/../../examples/bolt.crd")
+        ).expect("can't read bolt.crd");
+
+        let default_graph = sim_reparse(default_src);
+        let shell_graph = sim_reparse(&shell_src);
+        let bolt_graph = sim_reparse(&bolt_src);
+
+        let default_wgsl = cord_shader::generate_wgsl_from_trig(&default_graph);
+        let shell_wgsl = cord_shader::generate_wgsl_from_trig(&shell_graph);
+        let bolt_wgsl = cord_shader::generate_wgsl_from_trig(&bolt_graph);
+
+        assert_ne!(default_wgsl, shell_wgsl, "shell.crd should produce different WGSL than default");
+        assert_ne!(default_wgsl, bolt_wgsl, "bolt.crd should produce different WGSL than default");
+        assert_ne!(shell_wgsl, bolt_wgsl, "shell and bolt should produce different WGSL");
+
+        assert!(shell_graph.nodes.len() > 10, "shell should have a nontrivial graph");
+        assert!(bolt_graph.nodes.len() > 10, "bolt should have a nontrivial graph");
+    }
 }