fix(stop): the exit-4 refusal names where the holder may be (Issue #31, Mac review)

The refusal pointed at ~/.claude/sessions/ for every agent, whatever
CLAUDE_CONFIG_DIR said, and never mentioned a non-agent process naming the
uuid on its command line. The in-use CLI now prints, on stderr while the
conversation is in use, the adapter's in_use_hints: for every adapter
`ps -axww | grep <uuid>`, and for claude its real sessions/ dir first. stop
prints them under its refusal, and says "records preserved" instead of
"no state was modified": the gate runs after the kill chain, so the session
itself may already be down. SKILL.md's exit 4 row says the same; it is not
a code block, so no inventory hash moves.

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

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

@@ -289,12 +289,12 @@ fi
 # registry lock. Any answer but "free" (0) keeps everything.
 if [ "$PURGE" = "1" ] && [ -n "$PURGE_UUID" ]; then
   inuse_rc=0
-  "$(_delegate_py_bin)" -m lib_py.agents in-use "$AGENT" "$PURGE_UUID" "$TARGET_CWD" --wait 5 >/dev/null || inuse_rc=$?
+  inuse_hints="$("$(_delegate_py_bin)" -m lib_py.agents in-use "$AGENT" "$PURGE_UUID" "$TARGET_CWD" --wait 5 2>&1 >/dev/null)" || inuse_rc=$?
   if [ "$inuse_rc" != "0" ]; then
     echo "ERROR: conversation $PURGE_UUID is still held by a live agent process (rc=$inuse_rc)." >&2
-    echo "  Refusing purge — records preserved (no state was modified)." >&2
-    echo "  For claude, see the session files naming it under ~/.claude/sessions/." >&2
-    delegate_publish_event "$DELEGATE_JOB_ID" cancelled "purge aborted: conversation still in use; no state was modified" "$DELEGATE_JOB_TOKEN" "$DELEGATE_JOB_ATTEMPT"
+    echo "  Refusing purge — records preserved: the registry row and the conversation files are untouched (the session itself may already be down)." >&2
+    [ -n "$inuse_hints" ] && printf '%s\n' "$inuse_hints" >&2
+    delegate_publish_event "$DELEGATE_JOB_ID" cancelled "purge aborted: conversation still in use; records preserved" "$DELEGATE_JOB_TOKEN" "$DELEGATE_JOB_ATTEMPT"
     exit 4
   fi
 fi