fix nix package install phase for gsf binaries

nix/package.nix

@@ -20,8 +20,19 @@ pkgs.rustPlatform.buildRustPackage rec {
   installPhase = ''
     runHook preInstall
     mkdir -p $out/bin
-    cp target/release/gsf $out/bin/
+
-    cp target/release/gsfd $out/bin/
+    gsf_bin="$(find target -type f -path '*/release/gsf' | head -n1)"
+    gsfd_bin="$(find target -type f -path '*/release/gsfd' | head -n1)"
+
+    if [ -z "$gsf_bin" ] || [ -z "$gsfd_bin" ]; then
+      echo "failed to locate built binaries under target/*/release" >&2
+      find target -maxdepth 4 -type f | sed -n '1,200p' >&2
+      exit 1
+    fi
+
+    install -m755 "$gsf_bin" $out/bin/gsf
+    install -m755 "$gsfd_bin" $out/bin/gsfd
+
     runHook postInstall
   '';