fix(ha/cluster-init): enable Pacemaker maintenance-mode during DRBD sync

Even with both nodes in standby, Pacemaker's monitor operations keep running.
When the monitor sees DRBD is Primary on a standby node (that it didn't start),
it triggers a stop action — killing the initial sync after ~10 s.

Enable maintenance-mode after standby stops the existing resources but before
DRBD is manually brought up for the sync.  Maintenance-mode suspends all
start/stop/monitor actions so Pacemaker is completely hands-off during the
sync.  Disable it alongside crm_standby -v off once UpToDate/UpToDate is
confirmed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/ha/cluster-init.sh

@@ -152,11 +152,13 @@ for i in $(seq 1 30); do
 done
 
 # ── 2. DRBD initialisation ────────────────────────────────────────────────
-# Put both nodes in Pacemaker standby before touching DRBD metadata.
-# Without this, the OCF DRBD agent races: it sees drbdadm-down as a failure
-# and immediately calls drbdadm-up again, leaving the backing disk busy when
-# create-md / write-dev-uuid runs.  On a fresh cluster with no resources
-# configured this is a no-op; on a re-run it stops the race.
+# Put both nodes in Pacemaker standby first so it stops managed resources
+# cleanly, then enable maintenance-mode so Pacemaker's monitor operations are
+# suspended.  Without maintenance-mode, Pacemaker keeps monitoring: when it
+# sees DRBD Primary on a standby node (that it didn't start), it triggers a
+# stop action — killing the initial sync after ~10 s.  Maintenance-mode
+# disables all start/stop/monitor actions for the duration of the sync; it is
+# cleared after UpToDate/UpToDate is confirmed.
 log "Setting both nodes to Pacemaker standby for DRBD metadata init..."
 crm_standby -N "$NODE1" -v on 2>/dev/null || true
 crm_standby -N "$NODE2" -v on 2>/dev/null || true
@@ -174,6 +176,9 @@ for i in $(seq 1 30); do
   sleep 2
 done
 
+log "Enabling Pacemaker maintenance-mode (suspends monitor/start/stop during sync)..."
+crm_attribute -t crm_config -n maintenance-mode -v true 2>/dev/null || true
+
 log "Detaching DRBD on $NODE1 (belt-and-suspenders after standby)..."
 drbdadm down ha-data 2>/dev/null || true
 log "Detaching DRBD on $NODE2..."
@@ -277,7 +282,8 @@ while true; do
   sleep 3
 done
 
-log "Clearing Pacemaker standby — sync complete, handing DRBD back to Pacemaker..."
+log "Disabling Pacemaker maintenance-mode and clearing standby — handing DRBD back to Pacemaker..."
+crm_attribute -t crm_config -n maintenance-mode -v false 2>/dev/null || true
 crm_standby -N "$NODE1" -v off 2>/dev/null || true
 crm_standby -N "$NODE2" -v off 2>/dev/null || true