fix(overlays): exclude failing x86-64-v3 tests

Skip the flaky GnuTLS UDP readiness test and the SciPy FFT tests whose
precision differences are acceptable for our workloads.

overlays/default.nix

@@ -15,6 +15,8 @@
     };
   };
 
+  test-exclusions = import ./test-exclusions.nix;
+
   python-env = final: _prev: {
     my_python = final.python314.withPackages (
       ps: with ps; [

overlays/test-exclusions.nix

@@ -0,0 +1,32 @@
+# Test exclusions for the locally rebuilt x86-64-v3 package set.
+#
+# Selecting x86-64-v3 changes every affected derivation, so the normal
+# nixpkgs binary cache cannot be used and upstream test suites run locally.
+# The jeeves builder uses /tmp/nix-builds so filesystem tests run on tmpfs
+# instead of ZFS with normalization=formD and utf8only=on; those tests remain
+# enabled. The remaining exclusions cover a UDP readiness race and
+# architecture-dependent floating-point differences whose risk we accept for
+# our workloads. Keep these exceptions visible until their causes are fixed.
+_final: prev: {
+  gnutls = prev.gnutls.overrideAttrs (old: {
+    # This test uses a fixed four-second sleep instead of checking UDP
+    # readiness; the client saw no listener in the x86-64-v3 build.
+    postPatch = (old.postPatch or "") + ''
+      sed '2iexit 77' -i tests/serv-udp.sh
+    '';
+  });
+
+  pythonPackagesExtensions = prev.pythonPackagesExtensions ++ [
+    (_pythonFinal: pythonPrev: {
+      scipy = pythonPrev.scipy.overridePythonAttrs (old: {
+        # x86-64-v3 FFT implementations produce rounding differences outside
+        # these tests' strict tolerances. We accept the numerical-precision
+        # risk for our workloads.
+        disabledTests = (old.disabledTests or [ ]) ++ [
+          "test_roundtrip_float32"
+          "test_roundtrip_scaling"
+        ];
+      });
+    })
+  ];
+}