The PO read_messages gap (board agent soft-blocked on i_am_idle, unable to clear
unread A2A) was deploy-staleness: a PO spawned from an old manifest predating the
read_messages grant in _BOARD_DO. Current code is correct (verified: live
product-owner/head-marketing manifests carry it). Add a regression guard so the
grant can't silently drop from _BOARD_DO for board roles.