:l = *[1,2]

:@$ post run check
	|1,2,3,4: {l}

|1,2: {l}

l!insert(3)

|1,2,3: {l}

merge branch!

l!insert(4)

|1,2,3,4: {l}

merge branch!

l!insert(5)

|1,2,3,4,5: {l}
---

error("cancel merge")