monado: use opencv with protobuf_21 (#442919)

pkgs/by-name/mo/monado/package.nix

@@ -35,11 +35,13 @@
   libXrandr,
   nix-update-script,
   onnxruntime,
+  opencv4,
   openhmd,
   openvr,
   orc,
   pcre2,
   pkg-config,
+  protobuf_21,
   python3,
   SDL2,
   shaderc,
@@ -62,7 +64,14 @@
   serviceSupport ? true,
   tracingSupport ? false,
 }:
-
+let
+  # For some reason protobuf 32 causes a segfault during startup
+  # Pin to last (known) working version
+  # See https://github.com/NixOS/nixpkgs/issues/439075
+  opencv4' = opencv4.override {
+    protobuf = protobuf_21;
+  };
+in
 stdenv.mkDerivation (finalAttrs: {
   pname = "monado";
   version = "25.0.0";
@@ -124,8 +133,7 @@ stdenv.mkDerivation (finalAttrs: {
     libXext
     libXrandr
     onnxruntime
-    # FIXME: OpenCV support causes a segfault on start. See https://github.com/NixOS/nixpkgs/issues/439075
-    # opencv4
+    opencv4'
     openhmd
     openvr
     orc