List Sessions

List the project's V4 sessions — one row per session (its most recent run), most-recent first.

A session is a conversation: follow-up runs reuse the same public_session_id, so GET /api/v4/runs would list one row per RUN. This collapses to one row per SESSION directly in Postgres with DISTINCT ON, so a chatty session with 100 runs is still a single row (no scan amplification), and selects only the slim columns the session list needs — never the heavy per-run text/token/cost fields.

Keyset-paginated on the latest run's (created_at, id): pass next_cursor back as cursor to page. Offset/COUNT was dropped — it doesn't scale on projects with many sessions.