compilation failure "Unbound value MenhirLib.StaticVersion.require_20260203" with OCaml-5.4

Building on nixos-26.05 using OCaml 5.4 failed. Here is what I did :

$ git clone --recurse-submodules https://github.com/ocaml-mlx/mlx
$ cd mlx
$ dune build
File "mlx/parser.mly", line 776, characters 29-36:
Error: the token COMMENT is unused.
File "mlx/parser.mly", line 777, characters 30-39:
Error: the token DOCSTRING is unused.
File "mlx/parser.mly", line 779, characters 7-10:
Error: the token EOL is unused.
File "mlx/parser.mly", line 685, characters 7-22:
Error: the token GREATERRBRACKET is unused.
File "mlx/parser.mly", line 711, characters 7-16:
Error: the token LESSSLASH is unused.
File "ocamlmerlin_mlx/ocaml/preprocess/parser_raw.mly", line 865, characters 29-36:
Warning: the token COMMENT is unused.
File "ocamlmerlin_mlx/ocaml/preprocess/parser_raw.mly", line 866, characters 30-39:
Warning: the token DOCSTRING is unused.
File "ocamlmerlin_mlx/ocaml/preprocess/parser_raw.mly", line 868, characters 7-10:
Warning: the token EOL is unused.
File "ocamlmerlin_mlx/ocaml/preprocess/parser_raw.mly", line 773, characters 7-22:
Warning: the token GREATERRBRACKET is unused.
File "ocamlmerlin_mlx/ocaml/preprocess/parser_raw.mly", line 799, characters 7-16:
Warning: the token LESSSLASH is unused.
File "ocamlmerlin_mlx/ocaml/preprocess/recover/synthesis.ml", line 125, characters 24-38:
125 |             ) infinity (Lr1.reductions st)
                              ^^^^^^^^^^^^^^
Error (alert deprecated): G.Lr1.reductions
Please use [get_reductions]

File "ocamlmerlin_mlx/ocaml/preprocess/recover/synthesis.ml", line 206, characters 19-33:
206 |             ) acc (Lr1.reductions st)
                         ^^^^^^^^^^^^^^
Error (alert deprecated): G.Lr1.reductions
Please use [get_reductions]
File "ocamlmerlin_mlx/ocaml/preprocess/recover/gen_recover.ml", line 47, characters 13-27:
47 |           ) (Lr1.reductions st);
                  ^^^^^^^^^^^^^^
Error (alert deprecated): G.Lr1.reductions
Please use [get_reductions]
File "ocamlmerlin_mlx/ocaml/preprocess/parser_raw.mly", line 942, characters 0-9:
Warning: the precedence level assigned to GREATERDOT is never useful.
File "ocamlmerlin_mlx/ocaml/preprocess/parser_raw.ml", line 5, characters 2-42:
5 |   MenhirLib.StaticVersion.require_20260203
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: Unbound value MenhirLib.StaticVersion.require_20260203

But I do have the right menhirLib version :

$ ocamlfind query menhirLib
/nix/store/4pvzd76gsp4h7slcdw2pis75z8hg2l20-ocaml5.4.1-menhirLib-20260203/lib/ocaml/5.4.1/site-lib/menhirLib

As I said, I'm on nixos, so I wrote a short flake to get there (provide opam dependencies to dune). I can reproduce it if needed. It provides the following dependencies :

            ppxlib
            ocaml-compiler-libs
            merlin-lib
            menhir
            menhirSdk
            menhirLib
            cppo

Start by reproducing the failure with the reported Nix flake and dune build, then inspect ocamlmerlin_mlx/ocaml/preprocess/parser_raw.ml alongside synthesis.ml and gen_recover.ml. Check the Menhir-related dependency versions and the deprecated Lr1.reductions calls; done means the project builds successfully with OCaml 5.4 and the listed dependencies.