Accepts a batch of rrweb events for a single session window. Batches are idempotent per (sessionId, sequence) — the same batch submitted twice is stored once. When flush is final, the server dispatches the session for processing immediately; otherwise the session is left in a receiving state until a scheduled finalizer picks it up.
Public key prefixed with luc_pk_. Safe to expose in client-side code. For navigator.sendBeacon callers that cannot set headers, the key may also be passed as the api_key query parameter.
final tells the server this is the last batch for the session — typically sent from a beforeunload handler. final batches trigger immediate session processing.
normal, final Batch accepted.