(deck@steamdeck-oled ~)$ head -n30 .local/bin/{.codium.nix,codium}
==> .local/bin/.codium.nix <==
with (import <nixpkgs>) { };
mkShell {
  nativeBuildInputs = [
    pkg-config
    clang_18
    lld_18
  ];
  buildInputs = [
    vscodium
    neovim
    nixfmt
(let
  fenix = import (fetchTarball "https://github.com/nix-community/fenix/archive/main.tar.gz") { };
in
fenix.complete.toolchain)
    pre-commit
#   rustfmt
#   rustPackages.clippy
    alsa-lib
    udev
    vulkan-loader
    vulkan-headers
    vulkan-tools
    xorg.libX11
    xorg.libXrandr
    xorg.libXcursor
    xorg.libXi
    (android-studio.withSdk (androidenv.composeAndroidPackages { includeNDK = true; }).androidsdk)
    cargo-ndk
  ];

==> .local/bin/codium <==
#!/bin/sh
exec nix-shell --run codium "$(dirname "$(realpath $0)")"/.codium.nix

  shellHook = ''export LD_LIBRARY_PATH="''${LD_LIBRARY_PATH:+$LD_LIBRARY_PATH:}${
    pkgs.lib.makeLibraryPath [
      alsa-lib
      udev
      vulkan-loader
      libxkbcommon
    ]
  }"'';
  RUST_SRC_PATH = rustPlatform.rustLibSrc;
}

(deck@steamdeck-oled ~)$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 6.11.11-valve27-1-neptune-611-g60ef8556a811, SteamOS, noversion, 20260108.1`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.31.2+2`
 - channels(root): `"nixpkgs"`
 - nixpkgs: `/nix/store/ss16zjzngmqn3idqk8a8csh7x1xjkqf7-nixpkgs/nixpkgs`

--- stderr

  thread 'main' (7836) panicked at /build/fresh-0.1.86-vendor/bindgen-0.72.1/lib.rs:616:27:
  Unable to find libclang: "couldn't find any valid shared libraries matching: ['libclang.so', 'libclang-*.so', 'libclang.so.*', 'libclang-*.so.*'], set the `LIBCLANG_PATH` environment variable to a path where one of these files can be found (invalid: [])"
  stack backtrace:
     0: __rustc::rust_begin_unwind
     1: core::panicking::panic_fmt
     2: core::result::unwrap_failed
     3: core::result::Result<T,E>::expect
     4: bindgen::ensure_libclang_is_loaded::{{closure}}
     5: std::sync::once_lock::OnceLock<T>::get_or_init::{{closure}}
     6: std::sync::once_lock::OnceLock<T>::initialize::{{closure}}
     7: std::sync::poison::once::Once::call_once_force::{{closure}}
     8: std::sys::sync::once::futex::Once::call
     9: std::sync::poison::once::Once::call_once_force
    10: std::sync::once_lock::OnceLock<T>::initialize
    11: std::sync::once_lock::OnceLock<T>::get_or_try_init
    12: std::sync::once_lock::OnceLock<T>::get_or_init
    13: bindgen::ensure_libclang_is_loaded
    14: bindgen::Bindings::generate
    15: bindgen::Builder::generate
    16: build_script_build::bindgen
    17: build_script_build::main
    18: core::ops::function::FnOnce::call_once

For my project I have something like, for you change it up a bit because you are missing librquickjs:

  shellHook = ''export LD_LIBRARY_PATH="''${LD_LIBRARY_PATH:+$LD_LIBRARY_PATH:}${
    pkgs.lib.makeLibraryPath [
      alsa-lib
      udev
      wayland
      vulkan-loader
      libxkbcommon
    ]
  }"'';

1. Adding "${libclang.lib}/lib" to env.LIBCLANG_PATH
2. Adding clang to nativeBuildInputs

That compiles, but a test fails 😅

failures:

---- services::plugins::embedded::tests::test_extract_plugins stdout ----

thread 'services::plugins::embedded::tests::test_extract_plugins' (8842) panicked at crates/fresh-editor/src/services/plugins/embedded.rs:138:9:
assertion failed: path.is_some()


failures:
    services::plugins::embedded::tests::test_extract_plugins

test result: FAILED. 1388 passed; 1 failed; 1 ignored; 0 measured; 0 filtered out; finished in 1.09s