feat(pulls): support branch-validated stack reordering

Assisted-by: Codet:GPT-5-Codex

modules/task/pull_stack.go

@@ -120,6 +120,19 @@ func AddPullStackEntry(ctx stdctx.Context, login *config.Login, owner, repo stri
 	return &s, nil
 }
 
+// ReorderPullStack records the order of PR branches that are already linked.
+func ReorderPullStack(ctx stdctx.Context, login *config.Login, owner, repo string, id int64, pullIndices []int64) (*stack.Stack, error) {
+	var s stack.Stack
+	err := postStackJSON(ctx, login, fmt.Sprintf("/repos/%s/%s/stacks/%d/reorder", owner, repo, id),
+		struct {
+			PullIndices []int64 `json:"pull_indices"`
+		}{PullIndices: pullIndices}, http.StatusOK, &s)
+	if err != nil {
+		return nil, err
+	}
+	return &s, nil
+}
+
 // RestackPullStack queues a restack starting at the stack's base branch.
 func RestackPullStack(ctx stdctx.Context, login *config.Login, owner, repo string, id int64) error {
 	client := api.NewClient(login)