#3136: range.move pastes on the range's sheet and asks before replacing spilled values

Addresses CodeRabbit review on #3216:
- "Pass the resolved sheet to the paste step": a sheet-qualified move
  (`Two!B1:B2` with Sheet1 active) was checked on Two but pasted on the
  active sheet, replacing its data unasked. range.move now calls
  paste_special with the range's sheet.
- "Check spilled values in the drop destination": cells showing a dynamic
  array's spilled values hold no cell of their own, so the drop replaced
  them without the prompt. They now count as data, as in Excel
  (ISBLANK of a spill cell is FALSE, COUNTA counts it).

Tests: drag_and_drop_on_another_sheet_stays_on_that_sheet,
drag_and_drop_asks_before_replacing_spilled_values.

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

crates/engine/src/cmd/edit/clipboard.rs

@@ -165,8 +165,8 @@ pub(super) fn paste(s: &mut Session, p: &Json) -> Result<Json> {
 }
 
 /// Drag and drop (dragging the selection's border): moves `range` so its top-left cell lands on
-/// `to`, as Cut and Paste would. Like Excel, it asks before replacing cells that hold data (other
-/// than the moved cells themselves); run it again with `overwrite: true` to replace them. A
+/// `to`, as Cut and Paste would. Like Excel, it asks before replacing cells that hold data or show a
+/// spilled value (other than the moved cells themselves); run it again with `overwrite: true` to replace them. A
 /// refused or failed move leaves the clipboard as it was.
 pub(super) fn range_move(s: &mut Session, p: &Json) -> Result<Json> {
     let sheet = target_sheet(s, p)?;
@@ -178,11 +178,13 @@ pub(super) fn range_move(s: &mut Session, p: &Json) -> Result<Json> {
         if bool_param(p, "overwrite") != Some(true)
             && let Some(dest) = dest
             && let Some(sh) = s.doc()?.wb.sheet(sheet)
-            && sh.cells.iter_range(dest).any(|(c, cell)| !src.contains(c) && cell.has_content())
+            && (sh.cells.iter_range(dest).any(|(c, cell)| !src.contains(c) && cell.has_content())
+                || sh.spill.range(dest.start..=dest.end).any(|(c, v)| dest.contains(*c) && !src.contains(*c) && *v != Value::Empty))
         {
             return Err(EngineError::Confirm("There's already data here. Do you want to replace it?".into()));
         }
-        paste(s, &json!({"at": to.a1()}))
+        // On the range's sheet, which `paste` would leave to the active one.
+        paste_special(s, &json!({"what": "all", "at": to.a1(), "sheet": sheet}))
     });
     if moved.is_err() {
         s.clipboard = kept;

crates/engine/src/cmd/edit/tests.rs

@@ -381,6 +381,42 @@ fn drag_and_drop_asks_before_replacing_data() {
     assert!(s.execute("range.move", json!({"range": "C2"})).is_err(), "`to` is required");
 }
 
+#[test]
+fn drag_and_drop_asks_before_replacing_spilled_values() {
+    // Cells showing a dynamic array's spilled values hold no cell of their own, but they are data.
+    let mut s = Session::new();
+    s.new_workbook();
+    s.execute("cell.set", json!({"cell": "A1", "input": "=SEQUENCE(3)"})).unwrap();
+    s.execute("range.setValues", json!({"range": "C2:C3", "values": [["Kiwi"], ["Plum"]]})).unwrap();
+    let r = s.execute("range.move", json!({"range": "C2:C3", "to": "A2"}));
+    let Err(EngineError::Confirm(q)) = r else { panic!("{r:?}") };
+    assert_eq!(q, "There's already data here. Do you want to replace it?");
+    let sh = s.doc().unwrap().wb.active().unwrap();
+    assert_eq!(sh.value(CellRef::new(2, 2)), Value::text("Plum"));
+    s.execute("range.move", json!({"range": "C2:C3", "to": "A2", "overwrite": true})).unwrap();
+    let sh = s.doc().unwrap().wb.active().unwrap();
+    assert_eq!(sh.value(CellRef::new(1, 0)), Value::text("Kiwi"));
+}
+
+#[test]
+fn drag_and_drop_on_another_sheet_stays_on_that_sheet() {
+    // The move was checked on the range's sheet but pasted on the active one, replacing its data
+    // without asking.
+    let mut s = Session::new();
+    s.new_workbook();
+    s.execute("home.insertSheet", json!({"name": "Two"})).unwrap();
+    s.execute("range.setValues", json!({"range": "B1:B2", "values": [["Kiwi"], ["Plum"]]})).unwrap();
+    s.execute("sheet.activate", json!({"sheet": 0})).unwrap();
+    s.execute("cell.set", json!({"cell": "A1", "input": "Keep"})).unwrap();
+    s.execute("range.move", json!({"range": "Two!B1:B2", "to": "A1"})).unwrap();
+    let wb = &s.doc().unwrap().wb;
+    let two = wb.sheet_index("Two").unwrap();
+    assert_eq!(wb.sheet(0).unwrap().value(CellRef::new(0, 0)), Value::text("Keep"));
+    assert_eq!(wb.sheet(two).unwrap().value(CellRef::new(0, 0)), Value::text("Kiwi"));
+    assert_eq!(wb.sheet(two).unwrap().value(CellRef::new(1, 0)), Value::text("Plum"));
+    assert_eq!(wb.sheet(two).unwrap().value(CellRef::new(0, 1)), Value::Empty);
+}
+
 #[test]
 fn replace_case_insensitive() {
     assert_eq!(replace_ci("Apple apple APPLE", "apple", "pear"), "pear pear pear");