#1855: Backspace then Enter is one undo step

Backspace clears the cell (edit.clearContents) and opens an empty editor.
Committing that editor ran cell.set "" on the already-empty cell, which
recorded a second, empty undo step, so Ctrl+Z appeared to do nothing and
the next Ctrl+Z undid an unrelated earlier edit. Committing empty text
into an empty cell now runs no command.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/lib.rs

@@ -929,7 +929,19 @@ impl SheetApp {
             }
             self.toast = Some((msg, now_ms()));
         }
-        let r = if fill_selection {
+        // Committing nothing into an empty cell changes nothing: no undo step (#1855, Backspace has
+        // already cleared the cell as its own step).
+        let unchanged = !fill_selection
+            && !array
+            && text.is_empty()
+            && self
+                .session
+                .active()
+                .and_then(|d| d.wb.sheet(ed.sheet))
+                .is_some_and(|sh| sh.cell(ed.cell).is_none_or(|c| c.formula.is_none() && c.value == gridcraft_engine::core::Value::Empty));
+        let r = if unchanged {
+            Ok(json!({}))
+        } else if fill_selection {
             self.session.run("range.fill", json!({"input": text}))
         } else {
             self.session.run("cell.set", json!({"cell": ed.cell.a1(), "input": text, "array": array}))

crates/ui-egui/tests/interaction.rs

@@ -892,3 +892,22 @@ fn rotated_wrapped_text_is_drawn_rotated_inside_its_cell() {
         assert!(clip.width() < 70.0, "clip spans one 6-character column, got {clip:?}");
     }
 }
+
+#[test]
+fn undo_after_backspace_restores_the_cleared_cell() {
+    // #1855: Backspace clears the cell and opens an empty editor; committing it must not add a
+    // second, empty undo step, so one Ctrl+Z brings the value back and leaves other edits alone.
+    let mut h = harness(blank());
+    text(&mut h, "3200");
+    key(&mut h, Key::Enter, Modifiers::NONE);
+    click_cell(&mut h, "C5");
+    text(&mut h, "11750");
+    key(&mut h, Key::Enter, Modifiers::NONE);
+    click_cell(&mut h, "A1");
+    key(&mut h, Key::Backspace, Modifiers::NONE);
+    key(&mut h, Key::Enter, Modifiers::NONE);
+    assert_eq!(value(&h, "A1"), Value::Empty);
+    key(&mut h, Key::Z, Modifiers::COMMAND);
+    assert_eq!(value(&h, "A1"), Value::Number(3200.0));
+    assert_eq!(value(&h, "C5"), Value::Number(11750.0));
+}