Delete an edge (one fact)
Permanently delete one edge by UUID — both stores.
An edge carries one fact, so this is the single-fact delete (Zep's
vocabulary: the deletable object is the edge; the fact is the text
stored on it). The canonical, explicitly-named replacement for
DELETE /memories/{agent_id}/{memory_id}: same scoping, same
cascade. The response names the field edge_id to match the route.
DELETE
https://truememory-api.mvstg.com/memories/{agent_id}/edges/{edge_id}