BEGIN;

ALTER TABLE game_sessions
  ADD COLUMN assignment_mode TEXT CHECK (assignment_mode IN ('manual', 'random', 'server-assigned')),
  ADD COLUMN variant_id TEXT,
  ADD COLUMN variant_name TEXT;

CREATE INDEX game_sessions_variant_id_idx ON game_sessions(variant_id);
CREATE INDEX game_sessions_assignment_mode_idx ON game_sessions(assignment_mode);

COMMIT;