That was my initial thought seeing it for the first time. But also can get behind the override reason from the docs @tgerbet shared earlier

diff --git a/nixos/modules/services/web-apps/engelsystem.nix b/nixos/modules/services/web-apps/engelsystem.nix
index 669620debce5..343f2e1b7dc1 100644
--- a/nixos/modules/services/web-apps/engelsystem.nix
+++ b/nixos/modules/services/web-apps/engelsystem.nix
@@ -99,7 +99,11 @@ in {
       '';
 
     services.phpfpm.pools.engelsystem = {
-      phpPackage = pkgs.php81;
+      phpPackage = pkgs.php82.buildEnv {
+        extraConfig = ''
+          session.gc_maxlifetime = 604800
+        '';
+      };
       user = "engelsystem";
       settings = {
         "listen.owner" = config.services.nginx.user;
diff --git a/pkgs/servers/web-apps/engelsystem/default.nix b/pkgs/servers/web-apps/engelsystem/default.nix
index 53a33195f610..762b42391dd5 100644
--- a/pkgs/servers/web-apps/engelsystem/default.nix
+++ b/pkgs/servers/web-apps/engelsystem/default.nix
@@ -1,9 +1,10 @@
-{ lib, stdenv, fetchzip, php, writeText, nixosTests }:
+{ lib
+, stdenv
+, fetchzip
+, php82
+, nixosTests
+}:
 
-let
-  phpExt = php.withExtensions
-    ({ enabled, all }: with all; [ filter mysqlnd mysqli pdo pdo_mysql ]);
-in
 stdenv.mkDerivation rec {
   pname = "engelsystem";
   version = "3.5.0";
@@ -13,7 +14,7 @@ stdenv.mkDerivation rec {
     hash = "sha256-RbzAHBZN02u14WaLtq5EOh4XwIdHKvzX7NhDBhn/CaU=";
   };
 
-  buildInputs = [ phpExt ];
+  buildInputs = [ php82 ];
 
   installPhase = ''
     runHook preInstall
@@ -30,7 +31,7 @@ stdenv.mkDerivation rec {
 
     echo $(command -v php)
     # The patchShebangAuto function always used the php without extensions, so path the shebang manually
-    sed -i -e "1 s|.*|#\!${phpExt}/bin/php|" "$out/share/engelsystem/bin/migrate"
+    sed -i -e "1 s|.*|#\!${lib.getExe php82}|" "$out/share/engelsystem/bin/migrate"
     ln -s "$out/share/engelsystem/bin/migrate" "$out/bin/migrate"
 
     runHook postInstall
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 3a906641326c..b7e8a9d81ca9 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -25999,7 +25999,7 @@ with pkgs;
 
   dspam = callPackage ../servers/mail/dspam { };
 
-  engelsystem = callPackage ../servers/web-apps/engelsystem { php = php81; };
+  engelsystem = callPackage ../servers/web-apps/engelsystem { };
 
   envoy = callPackage ../servers/http/envoy {
     go = go_1_20;

kinda because php82 is

let
  base = callPackage ./generic.nix (_args // {
    version = "8.2.17";
    hash = "sha256-GRMWwgMmfZYWC0fSL5VdTcEXk96KXzJ+DCp2J1polOo=";
  });
in
base.withExtensions ({ all, ... }: with all; ([

In reply to @hexa:lossy.network
ok, I am stupid … my local staged changes do actually work.

No, not stupid, smart. Because now I had the opportunity to learn a few things I hadn't seen before ^^

It was for the greater good

It's the PHP default value https://www.php.net/manual/en/session.configuration.php#ini.session.gc-maxlifetime

It can be annoying if the app maintains authentication via the PHP session mechanism (also session.cookie_lifetime)