docs(stop): a purge removes the row; exit 4 covers a live agent (Issue #31)

The prose said a purge leaves a `terminated` row; the code removes it, and
the monitor never marks a stopped row. The step-5 list names what a claude
purge removes. The two code blocks (lines 52, 83) still say `terminated`:
changing them changes their inventory sha, which waits for approval.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.agents/skills/multi-agent-mux-stop/scripts/stop_session.sh

@@ -18,8 +18,8 @@
 #                              셋 다 실패하면 exit 2)
 #   --herdr-session <name>  — isolated herdr session name (alias: --herdr-server)
 #   --reason <reason>       — 상태 전이 사유 (stop_reason). 기본값 manual_stop
-#   --purge-conversation    — 디스크의 conversation artifact 까지 삭제.
-#                             status=terminated, resumable=false 로 전이하며
+#   --purge-conversation    — 디스크의 conversation artifact 와 세션 부속 경로까지
+#                             삭제하고 레지스트리 행(YAML+DB)을 지우며
 #                             resume 불가. --yes 없이는 확인 프롬프트(exit 3)
 #   --yes                   — --purge-conversation 의 확인 프롬프트 생략
 #
@@ -30,7 +30,7 @@
 # Exit codes:
 #   0 = success (or already-stopped no-op) | 1 = YAML not found / not registered
 #   2 = invalid args | 3 = interactive confirmation required (--yes 누락)
-#   4 = purge aborted (herdr session survived the kill chain)
+#   4 = purge aborted (herdr session or an agent process holding the conversation survived the kill chain)
 set -euo pipefail
 
 # shellcheck disable=SC1091
@@ -56,7 +56,7 @@ Arguments:
                              read from its registry row, not from where you stand.
   --reason <reason>    — stop_reason field (default: manual_stop)
   --purge-conversation — also delete on-disk conversation artifacts;
-                         status becomes terminated and resume is impossible
+                         the registry row is removed and resume is impossible
   --yes                — skip the --purge-conversation confirmation prompt
 EOF
 }