Compare median intra-command IATs of the two temporal halves of the
session. ≥ MULTI_ACTOR_HALF_MIN_COMMANDS (4) per half required;
relative delta > MULTI_ACTOR_HANDOFF_DELTA (0.5) → handoff_detected.
team_coordinated is Tier B (cross-session); never emitted from a
single session. Confidence 0.55 with both halves ≥ 8 commands; 0.40
otherwise.