fix(cli): make tracker iterators snapshot-safe

Co-Authored-By: Virgil <virgil@lethean.io>

pkg/cli/tracker.go

@@ -89,8 +89,11 @@ type TaskTracker struct {
 func (tr *TaskTracker) Tasks() iter.Seq[*TrackedTask] {
 	return func(yield func(*TrackedTask) bool) {
 		tr.mu.Lock()
-		defer tr.mu.Unlock()
+		tasks := make([]*TrackedTask, len(tr.tasks))
-		for _, t := range tr.tasks {
+		copy(tasks, tr.tasks)
+		tr.mu.Unlock()
+
+		for _, t := range tasks {
 			if !yield(t) {
 				return
 			}
@@ -102,8 +105,11 @@ func (tr *TaskTracker) Tasks() iter.Seq[*TrackedTask] {
 func (tr *TaskTracker) Snapshots() iter.Seq2[string, string] {
 	return func(yield func(string, string) bool) {
 		tr.mu.Lock()
-		defer tr.mu.Unlock()
+		tasks := make([]*TrackedTask, len(tr.tasks))
-		for _, t := range tr.tasks {
+		copy(tasks, tr.tasks)
+		tr.mu.Unlock()
+
+		for _, t := range tasks {
 			name, status, _ := t.snapshot()
 			if !yield(name, status) {
 				return

pkg/cli/tracker_test.go

@@ -189,6 +189,35 @@ func TestTaskTracker_Good(t *testing.T) {
 		assert.NotContains(t, out, "✓")
 		assert.NotContains(t, out, "✗")
 	})
+
+	t.Run("iterators tolerate mutation during iteration", func(t *testing.T) {
+		tr := NewTaskTracker()
+		tr.out = &bytes.Buffer{}
+
+		tr.Add("first")
+		tr.Add("second")
+
+		done := make(chan struct{})
+		go func() {
+			defer close(done)
+			for task := range tr.Tasks() {
+				task.Update("visited")
+			}
+		}()
+
+		require.Eventually(t, func() bool {
+			select {
+			case <-done:
+				return true
+			default:
+				return false
+			}
+		}, time.Second, 10*time.Millisecond)
+
+		for name, status := range tr.Snapshots() {
+			assert.Equal(t, "visited", status, name)
+		}
+	})
 }
 
 func TestTaskTracker_Bad(t *testing.T) {