The HTTP Cypher transport (the only implementation of Arcadic.Transport).
Reads go to /api/v1/query/<db> (server-enforced idempotent), writes to
/api/v1/command/<db>. The arcadedb-session-id header is echoed on every
request whenever conn.session_id is set, so reads and writes inside a
transaction are session-scoped. Req's own client retry is disabled — retry
semantics are the caller's (retries: body param) and the error taxonomy's.