fix: simplify parallel map using channels (#582)

packages/tui/internal/util/concurrency_test.go

@@ -0,0 +1,23 @@
+package util_test
+
+import (
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/sst/opencode/internal/util"
+)
+
+func TestWriteStringsPar(t *testing.T) {
+	items := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
+	sb := strings.Builder{}
+	util.WriteStringsPar(&sb, items, func(i int) string {
+		// sleep for the inverse duration so that later items finish first
+		time.Sleep(time.Duration(10-i) * time.Millisecond)
+		return strconv.Itoa(i)
+	})
+	if sb.String() != "0123456789" {
+		t.Fatalf("expected 0123456789, got %s", sb.String())
+	}
+}