feat(resume): resume ensures the monitor daemon (Issue #72, decision 2)

Only create started the per-workspace monitor, and only on its job path, so
the stop -> update -> resume flow the update skill requires left no monitor.
resume now calls start_watchdog with the control root as workdir (as create
does since #21 A8, also for a worktree session) after the row is written, on
both the already-running and the spawn path. MAM_NO_SUBSCRIBER_DAEMON=1 starts
none; a failure warns and does not fail the resume.

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

.agents/skills/multi-agent-mux-resume/scripts/resume_session.sh

@@ -154,6 +154,18 @@ if [ -z "$UUID" ]; then
   esac
 fi
 
+# Issue #72: a resumed session gets the monitor daemon create starts - the
+# control root's (Issue #21 A8), also for a worktree --workspace. Called after
+# the row is written; MAM_NO_SUBSCRIBER_DAEMON=1 starts none. Never fails the resume.
+_ensure_monitor_daemon() {
+  local wd_pid
+  if wd_pid=$(start_watchdog "resume" "$WORKSPACE_ROOT"); then
+    echo "watchdog PID: $wd_pid"
+  else
+    echo "WARNING: could not start the monitor daemon of '$WORKSPACE_ROOT'; the session itself was resumed" >&2
+  fi
+}
+
 # 2. If herdr is alive, print warning or attach.
 if [ "$HERDR_ALIVE" = "1" ]; then
   if [ "${DRY_RUN:-0}" = "1" ]; then
@@ -166,6 +178,7 @@ if [ "$HERDR_ALIVE" = "1" ]; then
     --session "$SESSION_NAME" --uuid "$UUID" --agent "$AGENT" --workspace "$WORKSPACE" \
     --herdr-session "$HERDR_SESSION_NAME" --already-running \
     ${HERDR_WORKSPACE_OPT:+--herdr-workspace "$HERDR_WORKSPACE_OPT"}
+  _ensure_monitor_daemon
   exit 0
 fi
 
@@ -274,5 +287,6 @@ CONTROL_PLANE_JSON="$CP_JSON" bash "$(dirname "${BASH_SOURCE[0]}")/update_yaml_r
   --herdr-session "$HERDR_SESSION_NAME" --cmd-full "$CMD_FULL" \
   ${DROP_FLAG:+$DROP_FLAG} \
   ${HERDR_WORKSPACE_OPT:+--herdr-workspace "$HERDR_WORKSPACE_OPT"}
+_ensure_monitor_daemon
 
 echo "Successfully resumed $SESSION_NAME ($AGENT)"