List sessions (conversation-label rollups)
Use when: caller wants the multi-turn view: traces grouped by their session label (conversation id), with per-session trace counts and cost
Groups traces by session label and returns one row per label with trace count, total cost, first-seen and last-active timestamps. Sessions are labels, not lifecycle objects — a row with a NULL label aggregates all unlabeled traces.
Authorizations
Verlon API key (newly minted keys are prefixed sk-vrln-; legacy verlon_* and layer_* keys from prior prefix migrations continue to validate). Generated from the dashboard under Settings → API Keys, or via verlon key create in the CLI.
Response
Session rollup rows, most recently active first.

