Classifies session kinds into FREE (cron, heartbeat, subagent, team) vs
ENFORCED (DM, group, ws, default, unknown, empty). FREE kinds compose
targets per job spec; everything else must match the ctx-bound origin.
postCrossTargetNotice posts the audit breadcrumb back to the origin
chat when an explicit forward succeeds: msgBus preferred, falls back to
direct sender, else slog.Warn so the skip is traceable.
