Both PvP clients received turnState:0 ('both go first'). BuildBattleStart
now takes turnState; the Loaded arm assigns 0 to A, 1 to B — no Type check,
correct in Scripted (real player = A = first) and PvP (first arriver first).
Updated three existing BuildBattleStart callers in the test suite to pass
turnState:0 (the param is now required).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>