try fix script

lib.nix

@@ -1,7 +1,7 @@
 { pkgs }:
 let
   inherit (pkgs) lib;
-  runtime = "$(realpath .compose)";
+  runtime = ".compose";
 in
 {
   mkWrapper =
@@ -142,8 +142,8 @@ in
         name = "run-postgres";
         text = ''
           set -euo pipefail
-          PGDATA=${data_dir}
-          PGHOST=${runtimeDir}
+          PGDATA=$(realpath ${data_dir})
+          PGHOST=$(realpath ${runtimeDir})
           PGPORT=${builtins.toString port}
           export PGDATA PGHOST PGPORT
           mkdir -p ${lib.escapeShellArg runtimeDir}