fix: resolve crane IFD cross-compilation issues

The issue was that crane's modifiedSrc derivation (which copies external
Cargo.lock files) was being created with the target platform's stdenv,
causing system conflicts during cross-compilation evaluation.

Fixed by:
- Using buildPackages.stdenv for the modifiedSrc derivation so it runs on
  the build platform during evaluation
- Adding preferLocalBuild and allowSubstitutes flags to ensure proper IFD handling
- Re-enabling crane for pg_jsonschema to test the fix

This resolves the 'required system not available' errors while maintaining
crane's incremental build benefits for native builds.

Author: yvan-sraka

nix/cargo-pgrx/buildPgrxExtension.nix

@@ -33,6 +33,7 @@
   pkg-config,
   rustPlatform,
   stdenv,
+  buildPackages,
   writeShellScriptBin,
   defaultBindgenHook,
 }:
@@ -155,10 +156,15 @@ let
   # Copy external Cargo.lock into source directory to satisfy crane's requirements
   modifiedSrc =
     if useCrane && hasExternalLockFile then
-      stdenv.mkDerivation {
+      # Use buildPackages.stdenv to ensure this runs on the build platform
+      # This derivation just copies files and should be buildable during evaluation
+      buildPackages.stdenv.mkDerivation {
         name = "${args.pname or "source"}-with-lockfile";
         src = args.src;
         dontBuild = true;
+        # Ensure this derivation runs locally during evaluation
+        preferLocalBuild = true;
+        allowSubstitutes = false;
         installPhase = ''
           cp -r $src $out
           chmod -R u+w $out

nix/cargo-pgrx/mkPgrxExtension.nix

@@ -59,9 +59,8 @@ let
   # Initialize crane with the same Rust toolchain as rustPlatform to ensure consistency.
   # crane.mkLib creates a library of crane functions bound to a specific package set,
   # then we override the toolchain to match the pgrx-required Rust version.
-  # Disable crane for cross-compilation to avoid system conflicts
   craneLib =
-    if useCrane && (stdenv.buildPlatform.system == stdenv.hostPlatform.system) then
+    if useCrane then
       assert crane != null;
       (crane.mkLib pkgs).overrideToolchain rust-bin.stable.${rustVersion}.default
     else

nix/ext/pg_jsonschema/default.nix

@@ -15,7 +15,7 @@ let
       cargo = rust-bin.stable.${rustVersion}.default;
       mkPgrxExtension = callPackages ../../cargo-pgrx/mkPgrxExtension.nix {
         inherit rustVersion pgrxVersion;
-        useCrane = false;
+        useCrane = true;
       };
       src = fetchFromGitHub {
         owner = "supabase";