-- Keyset (cursor) pagination for conversation message history.
--
-- An ever-growing single conversation — notably a desktop companion's ONE
-- session, which now also absorbs every IM-channel turn — is loaded in
-- newest-first windows via a (created_at, id) keyset cursor instead of one
-- giant fetch:
--
--   SELECT * FROM messages
--   WHERE conversation_id = ?
--     AND type NOT IN ('cron_trigger','skill_suggest')
--     AND (created_at < ? OR (created_at = ? AND id < ?))
--   ORDER BY created_at DESC, id DESC
--   LIMIT ?
--
-- The existing idx_messages_conv_created / idx_messages_conv_created_desc cover
-- (conversation_id, created_at) but NOT the `id` tiebreaker, so the cursor's
-- (created_at, id) comparison and the matching ORDER BY degrade to a sort. This
-- composite covers both, keeping deep "load older" pages index-only and stable
-- under concurrent streaming appends. `id` is msg_{uuidv7} (time-ordered), so it
-- is a sound, monotonic tiebreaker for rows sharing a created_at millisecond.
CREATE INDEX IF NOT EXISTS idx_messages_conv_created_id
    ON messages (conversation_id, created_at DESC, id DESC);