-- Which team engine a mission uses, or none.
--
-- NULL           solo — one agent, no fan-out beyond the subagents it chooses.
--                The default, deliberately: Anthropic measure multi-agent at
--                3-10x the tokens of a single session, with wall-clock often
--                LONGER, since the benefit is thoroughness rather than speed.
-- 'claude_code'  Claude Code agent teams inside the mission's VM. The lead
--                decides its own team size; in-process teammates live in the
--                lead's process, so one VM hosts the whole team.
-- 'zeroclaw'     the existing graph engine (tier='team'), whose assets are
--                durability and per-node heterogeneity.
--
-- No CHECK constraint. Two engines are selectable today and the composed shape
-- (a ZeroClaw graph whose leaves are Claude-Code VMs) will add a third name; a
-- constraint here would mean a migration to learn a new word.
ALTER TABLE missions
    ADD COLUMN IF NOT EXISTS team_engine text;