mount_beads.sh: verify mount succeeded via mtab

mcptools/mount_beads.sh

@@ -23,4 +23,11 @@ fi
 MOUNT=$(uuidgen | cut -d- -f1)
 
 echo "mount $CWD $MOUNT" | 9p write anvillm/beads/ctl
+
+# Verify mount succeeded
+if ! 9p read anvillm/beads/mtab 2>/dev/null | grep -q "^$MOUNT	"; then
+    echo "error: mount failed for $CWD" >&2
+    exit 1
+fi
+
 echo "$MOUNT"