Bulk-import sessions (contacts). The body must be { "sessions": [...] }. Every entry is matched against an existing contact before anything is created — by userId when the row carries one, otherwise by email — so importing the same list twice updates those contacts instead of duplicating them. Returns the ids of the imported sessions.

At most MAX_IMPORT_SESSIONS_PER_REQUEST rows per call: a request has to finish well inside the edge's 60s window, and a larger list belongs in a sequence of these calls. Oversized bodies are rejected rather than truncated.