A subagent's opening prompt is easy to work past, and the PreToolUse reminder only fires after five quiet minutes, so a short subagent can finish without posting. The opening now says posting is a completion requirement, and SubagentStop blocks a context that never ran `vibescrobble post`. Contexts without vibescrobble or didbot are not blocked. Change-Id: Ie352dc1692b5e0db20303f20b69a2a1cc81c4d15