joinmarket: fix for NixOS 25.11

Temporarily add nixpkgs-25.05 for joinmarket (see code comment).

pkgs/default.nix

@@ -8,6 +8,11 @@ in
     config = {};
     overlays = [];
   }
+, pkgs-25_05 ? import nixpkgsPinned.nixpkgs-25_05 {
+    inherit (pkgs.stdenv.hostPlatform) system;
+    config = {};
+    overlays = [];
+  }
 }:
 let self = {
   clightning-rest = pkgs.callPackage ./clightning-rest { inherit (self) fetchNodeModules; };
@@ -43,7 +48,7 @@ let self = {
   generate-secrets = import ./generate-secrets-deprecated.nix;
   nixops19_09 = pkgs.callPackage ./nixops { };
 
-  pinned = import ./pinned.nix pkgs pkgsUnstable;
+  pinned = import ./pinned.nix pkgs pkgsUnstable pkgs-25_05;
 
   modulesPkgs = self // self.pinned;
 }; in self

pkgs/joinmarket/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, lib, fetchFromGitHub, python3, nbPython3PackagesJoinmarket }:
+{ stdenv, lib, fetchFromGitHub, nbPython3PackagesJoinmarket }:
 
 let
   # Note:
@@ -18,7 +18,7 @@ let
     matplotlib # for ob-watcher
   ];
 
-  pythonEnv = python3.withPackages (_: runtimePackages);
+  pythonEnv = nbPython3PackagesJoinmarket.python.withPackages (_: runtimePackages);
 in
 stdenv.mkDerivation {
   pname = "joinmarket";

pkgs/nixpkgs-pinned.nix

@@ -17,4 +17,5 @@ in
 {
   nixpkgs = fetch lockedInputs.nixpkgs;
   nixpkgs-unstable = fetch lockedInputs.nixpkgs-unstable;
+  nixpkgs-25_05 = fetch lockedInputs.nixpkgs-25_05;
 }

pkgs/pinned.nix

@@ -1,5 +1,5 @@
 # This file is generated by ../helper/update-flake.nix
-pkgs: pkgsUnstable:
+pkgs: pkgsUnstable: pkgs-25_05:
 {
   inherit (pkgs)
     bitcoin
@@ -21,5 +21,5 @@ pkgs: pkgsUnstable:
   inherit (pkgsUnstable)
     ;
 
-  inherit pkgs pkgsUnstable;
+  inherit pkgs pkgsUnstable pkgs-25_05;
 }

pkgs/python-packages/default.nix

@@ -21,18 +21,27 @@ rec {
       sha256 = callPackage ./sha256 {};
 
       joinmarket = callPackage ./joinmarket { inherit (nbPkgs.joinmarket) version src; };
-
-      ## Specific versions of packages that already exist in nixpkgs
-
-      # autobahn 20.12.3, required by joinmarketclient
-      autobahn = callPackage ./specific-versions/autobahn.nix {};
     };
 
   nbPython3Packages = (python3.override {
     packageOverrides = pyPkgsOverrides;
   }).pkgs;
 
-  nbPython3PackagesJoinmarket = nbPython3Packages;
+  # joinmarket requires cython 3.0 via pkg bencoder.pyx.
+  # The python pkgs from nixpkgs-25.11 default to cython 3.1.
+  # Downgrading to 3.0 causes mass rebuilds, so we use python pkgs from nixpkgs-25.05 for joinmarket.
+  # The nixpkgs-25.05 dependency will be removed with the next joinmarket update.
+  # https://github.com/JoinMarket-Org/joinmarket-clientserver/issues/1787
+  nbPython3PackagesJoinmarket =
+    (nbPkgs.pinned.pkgs-25_05.python3.override {
+      packageOverrides = self: super:
+        (pyPkgsOverrides self super) // {
+          ## Specific versions of packages that already exist in nixpkgs
+
+          # autobahn 20.12.3, required by joinmarketclient
+          autobahn = self.callPackage ./specific-versions/autobahn.nix {};
+        };
+    }).pkgs;
 
   # Re-enable pkgs `hwi`, `trezor` that are unaffected by `CVE-2024-23342` because
   # they don't use python pkg `ecdsa` for signing.