// probeBuiltByModel tells if the node key needed a model call: a leaf whose
// source is over nodeBytes, or a merge whose children do not fit in one node.
-func probeBuiltByModel(memory *Memory, key nodeKey) (bool, error) {
+func probeBuiltByModel(memory *Memory, key NodeKey) (bool, error) {
if key.level == 0 {
message, err := memory.log.Message(key.index)
if err != nil {