Queue move: saturate a huge relative offset instead of overflowing (#532)

crates/engine/src/export_tests.rs

@@ -359,6 +359,22 @@ fn queue_orders_cancels_and_retries() {
     assert!(queue(&mut s).is_empty());
 }
 
+#[test]
+fn queue_move_by_extreme_offsets_clamps_instead_of_overflowing() {
+    let mut s = demo();
+    let ids: Vec<u64> = (0..3)
+        .map(|_| {
+            let r = s.execute("export.queue.add", json!({"preset": "Waveform Audio 48 kHz 16-bit", "path": "queued-output/"})).unwrap();
+            r["added"][0].as_u64().unwrap()
+        })
+        .collect();
+    let order = |s: &mut Session| -> Vec<u64> { queue(s).iter().map(|i| i["id"].as_u64().unwrap()).collect() };
+    s.execute("export.queue.move", json!({"id": ids[1], "by": i64::MAX})).unwrap();
+    assert_eq!(order(&mut s), [ids[0], ids[2], ids[1]]);
+    s.execute("export.queue.move", json!({"id": ids[1], "by": i64::MIN})).unwrap();
+    assert_eq!(order(&mut s), [ids[1], ids[0], ids[2]]);
+}
+
 #[test]
 fn queue_cancels_a_running_export_and_retries_a_failed_one() {
     let mut s = demo();

crates/engine/src/export_tools.rs

@@ -769,7 +769,7 @@ fn queue_move(s: &mut Session, p: &Value) -> Result<Value> {
     let n = s.export_queue.items.len() as i64;
     let to = match (p.get("to").and_then(Value::as_i64), p.get("by").and_then(Value::as_i64)) {
         (Some(t), _) => t,
-        (None, Some(b)) => i as i64 + b,
+        (None, Some(b)) => (i as i64).saturating_add(b),
         _ => return Err(bad(cmd, "need `to` (index) or `by` (±n)")),
     }
     .clamp(0, n - 1) as usize;