fix(stop): a row-less stop uses the environment's server; only "no row" is row-less (Issue #71)

With no --herdr-session the server is chosen as create_session.sh chose
it (HERDR_SESSION_NAME, else the workspace's), not always derived from
the workspace. The row-less path runs only when the lookup says the row
is missing (exit 7); any other lookup failure stops with exit 1 as
before. Pins of the shifted stop_session.sh lines updated.

Refs #71

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

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

@@ -106,6 +106,7 @@ if [ "$PURGE" = "1" ]; then
   trap 'rm -f "$WORKSPACE_ROOT/.mam/purging-$SESSION_NAME"' EXIT
 fi
 
+AMBIENT_HERDR_SESSION="${HERDR_SESSION_NAME:-}"
 if [ -n "$HERDR_SERVER_OPT" ]; then
   export HERDR_SESSION_NAME="$HERDR_SERVER_OPT"
 else
@@ -116,12 +117,17 @@ fi
 # Issue #71: a session with no registry row (its create/resume died before
 # registering it) is closed here - herdr only, the registry is left alone. It
 # has no agent kind, so --agent is not needed. Only a session herdr runs
-# inside this workspace is closed; anything else changes nothing.
+# inside this workspace is closed; anything else changes nothing. With no row
+# the server is chosen as create_session.sh chose it: --herdr-session, else
+# the environment's HERDR_SESSION_NAME, else the workspace's server.
 stop_rowless() {
   if [ "$PURGE" = "1" ]; then
     echo "ERROR: session '$SESSION_NAME' not in $AGENT_SESSIONS_YAML; --purge-conversation needs its row. Nothing changed." >&2
     exit 1
   fi
+  if [ -z "$HERDR_SERVER_OPT" ] && [ -n "$AMBIENT_HERDR_SESSION" ] && [ "$AMBIENT_HERDR_SESSION" != "default" ]; then
+    export HERDR_SESSION_NAME="$AMBIENT_HERDR_SESSION"
+  fi
   local info cwd
   info=$(herdr agent get "$SESSION_NAME" 2>/dev/null) || info=""
   if [ -z "$info" ]; then
@@ -173,7 +179,13 @@ for s in d.get('herdr_sessions', []):
                           'delegate_job_logs_dir': cp.get('delegate_job_logs_dir', '') or ''}))
         sys.exit(0)
 sys.exit(7)
-") || stop_rowless
+") || MAPPED_RC=$?
+# 7 = no row; any other failure (registry unreadable) stops as before.
+[ "${MAPPED_RC:-0}" -ne 7 ] || stop_rowless
+if [ "${MAPPED_RC:-0}" -ne 0 ]; then
+  echo "ERROR: cannot read the row of '$SESSION_NAME' from $AGENT_SESSIONS_YAML" >&2
+  exit 1
+fi
 
 # --agent 미지정 시 레지스트리 기록으로 해석 (B-21).
 # ① row['agent'] → ② 세션명 접미사 → ③ pane.cmd 순. 셋 다 실패하면