Set the system path to a fixed location.

nix/modules/environment.nix

@@ -8,10 +8,52 @@
     };
   };
 
-  config = {
-    environment.etc."profile.d/system-manager-path.sh".source =
-      pkgs.writeShellScript "system-manager-path.sh" ''
-        export PATH=${lib.makeBinPath config.environment.systemPackages}:''${PATH}
-      '';
-  };
+  config =
+    let
+      pathDir = "/run/system-manager/sw";
+    in
+    {
+      environment.etc = {
+        "profile.d/system-manager-path.sh".source =
+          pkgs.writeText "system-manager-path.sh" ''
+            export PATH=${pathDir}/bin/:''${PATH}
+          '';
+
+        # TODO: figure out how to properly add fish support. We could start by
+        # looking at what NixOS and HM do to set up the fish env.
+        #"fish/conf.d/system-manager-path.fish".source =
+        #  pkgs.writeTextFile {
+        #    name = "system-manager-path.fish";
+        #    executable = true;
+        #    text = ''
+        #      set -gx PATH "${pathDir}/bin/" $PATH
+        #    '';
+        #  };
+      };
+
+      systemd.services.system-manager-path = {
+        enable = true;
+        description = "";
+        wantedBy = [ "system-manager.target" ];
+        serviceConfig = {
+          Type = "oneshot";
+          RemainAfterExit = true;
+        };
+        script =
+          let
+            pathDrv = pkgs.buildEnv {
+              name = "system-manager-path";
+              paths = config.environment.systemPackages;
+              pathsToLink = [ "/bin" ];
+            };
+          in
+          ''
+            mkdir --parents $(dirname "${pathDir}")
+            if [ -L "${pathDir}" ]; then
+              unlink "${pathDir}"
+            fi
+            ln --symbolic --force "${pathDrv}" "${pathDir}"
+          '';
+      };
+    };
 }