Address soundness hole in cycle prevention

benches/patterns/diamond.rs

@@ -1,7 +1,7 @@
 //! Diamond pattern benchmarks (fan-out then fan-in)
 
 use criterion::Criterion;
-use dagx::{task_fn, DagRunner};
+use dagx::{task_fn, DagRunner, TaskHandle};
 use futures::FutureExt;
 
 pub fn bench_diamond(c: &mut Criterion) {
@@ -13,14 +13,15 @@ pub fn bench_diamond(c: &mut Criterion) {
                 let dag = DagRunner::new();
 
                 for i in 0..50 {
-                    let source = dag.add_task(task_fn(move |_: ()| async move { i }));
+                    let source: TaskHandle<_> =
+                        dag.add_task(task_fn(move |_: ()| async move { i })).into();
 
                     let left = dag
                         .add_task(task_fn(|x: i32| async move { x * 2 }))
-                        .depends_on(&source);
+                        .depends_on(source);
                     let right = dag
                         .add_task(task_fn(|x: i32| async move { x * 3 }))
-                        .depends_on(&source);
+                        .depends_on(source);
 
                     dag.add_task(task_fn(|(l, r): (i32, i32)| async move { l + r }))
                         .depends_on((&left, &right));