Prepare MariaDB restore tests and recover backup disk space safely

lib/restore-test-remote.sh

@@ -7,6 +7,18 @@ source "$LIB_DIR/common.sh"
 CONFIG_FILE=${1:?Missing config}
 shift
 load_config
+if [[ ${1:-} == space ]]; then
+  # Local maintenance requested between components, while the parent holds FD 9.
+  [[ /proc/$PPID/fd/9 -ef $LOCKFILE ]] || die 'Space recovery requires the parent backup lock'
+  [[ ${2:-} =~ ^[0-9]+$ && $# == 2 ]] || die 'Invalid space request'
+  guard_workspaces
+  # shellcheck source=lib/space.sh
+  source "$LIB_DIR/space.sh"
+  clean_backup_scratch
+  MIN_FREE_GB=$(python3 -c 'import math,sys; print(math.ceil(float(sys.argv[1])))' "$RESTORE_TEST_MIN_FREE_GB")
+  ensure_space "$WORKDIR" "$2"
+  exit 0
+fi
 check_remote >&2
 # rclone is restricted to read operations here, including metadata reads.
 case ${1:-} in lsf|cat) rc "$@" ;; *) die 'Unsupported restore-test remote operation' ;; esac