Integration: test stringID blend modes through .atn import (#8502)

The PR's test only called blend_label/blend_ps. This adds one through the
import entry point: a Set Lyr step with Md enm("BlnM","softLight") and a
Make layer step with Usng Md "luminosity", written with atn::write and
imported, must give layer.setProps blend "Soft Light" and layer.new.layer
mode "Luminosity" with no unsupported steps. Without the PR's table rows
the Set step is unsupported (and the Make falls back to Normal).

Co-authored-by: justinjohn0306 <34035011+justinjohn0306@users.noreply.github.com>
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/engine/src/atn_cmds/tests.rs

@@ -30,6 +30,32 @@ fn blend_modes_accept_photoshop_string_ids_and_export_canonical_char_ids() {
     }
 }
 
+/// #8454: a Set and a Make layer step whose blend mode is stored as a Photoshop stringID import
+/// with that mode (a Set was unsupported, a Make silently fell back to Normal).
+#[test]
+fn layer_steps_with_string_id_blend_modes_import_with_their_mode() {
+    let set = desc("null").with("null", target_ref("Lyr ")).with("T   ", D::Descriptor(desc("Lyr ").with("Md  ", enm("BlnM", "softLight"))));
+    let make = desc("null").with("null", class_ref("Lyr ")).with("Usng", D::Descriptor(desc("Lyr ").with("Md  ", enm("BlnM", "luminosity"))));
+    let file = AtnFile {
+        name: UnicodeString::new_nul("Blend"),
+        expanded: false,
+        actions: vec![AtnAction {
+            name: UnicodeString::new_nul("A"),
+            items: vec![item("setd", "Set", Some(set)), item("Mk  ", "Make", Some(make))],
+            ..Default::default()
+        }],
+        warnings: vec![],
+    };
+    let imp = import(&atn::write(&file).unwrap()).unwrap();
+    assert!(imp.unsupported.is_empty(), "{:?}", imp.unsupported.iter().map(|u| &u.event).collect::<Vec<_>>());
+    let steps = &imp.actions[0].steps;
+    assert_eq!(steps.len(), 2);
+    assert_eq!(steps[0].0, "layer.setProps");
+    assert_eq!(steps[0].1["blend"], json!("Soft Light"));
+    assert_eq!(steps[1].0, "layer.new.layer");
+    assert_eq!(steps[1].1["mode"], json!("Luminosity"));
+}
+
 fn item(event: &str, label: &str, d: Option<Descriptor>) -> AtnItem {
     let event = match event.as_bytes() {
         [a, b, c, dd] => AtnEvent::Code([*a, *b, *c, *dd]),