Explain how two nodes of the relation graph are connected. Requires source and target. Optional max_depth (default 4). Edges are followed in both directions, so an indirect connection is found even when no single relation points from one to the other. Edges with valid_to are no longer true and must be reported as past, never as current. Node ids are typed "type:id" strings such as person:alex or tech:vue; the optional graph parameter selects a namespace and defaults to "memory".
