diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6cc5310..66c54e7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -120,6 +120,7 @@ jobs:
             --version "${{ env.LLVM_VERSION }}"
             --archive "${{ matrix.llvm-archive }}"
             --dest /project/.llvm
+            --prefix-file /project/.llvm-prefix
           CIBW_REPAIR_WHEEL_COMMAND_LINUX: >-
             auditwheel repair --plat ${{ matrix.auditwheel-plat }} -w {dest_dir} {wheel}
 
@@ -135,6 +136,7 @@ jobs:
             --version "${{ env.LLVM_VERSION }}"
             --archive "${{ matrix.llvm-archive }}"
             --dest "${{ github.workspace }}/.llvm"
+            --prefix-file "${{ github.workspace }}/.llvm-prefix"
 
           # Windows wheels are built on the hosted runner. The CMake install
           # step copies LLVM-C.dll next to llvm/__init__.pyd.
@@ -146,6 +148,7 @@ jobs:
             --version "${{ env.LLVM_VERSION }}"
             --archive "${{ matrix.llvm-archive }}"
             --dest "${{ github.workspace }}\\.llvm"
+            --prefix-file "${{ github.workspace }}\\.llvm-prefix"
 
       - name: Check wheel metadata
         shell: bash
diff --git a/run_tests.py b/run_tests.py
index 4e20296..51ccbe6 100755
--- a/run_tests.py
+++ b/run_tests.py
@@ -181,9 +181,11 @@ def run_regression_tests():
         # Print progress
         print(f"[{status}] {test_name}")
 
-        # Show error output if failed
-        if status == "FAIL" and stderr:
-            for line in stderr.splitlines()[:10]:  # First 10 lines of error
+        # Show captured output if failed. Pytest usually writes assertion
+        # details to stdout, while crashes/import errors often use stderr.
+        if status == "FAIL":
+            failure_output = stderr or stdout
+            for line in failure_output.splitlines()[:20]:
                 print(f"       {line}")
 
     # Summary
diff --git a/tests/regressions/test_ollvm_obf_semantic_parity.py b/tests/regressions/test_ollvm_obf_semantic_parity.py
index 276d226..3bc69df 100644
--- a/tests/regressions/test_ollvm_obf_semantic_parity.py
+++ b/tests/regressions/test_ollvm_obf_semantic_parity.py
@@ -17,6 +17,7 @@ from functools import lru_cache
 from pathlib import Path
 import shutil
 import subprocess
+import sys
 import textwrap
 
 import pytest
@@ -478,6 +479,10 @@ def find_clang() -> Path | None:
 
 
 @lru_cache(maxsize=1)
+def is_x86_target(target: str) -> bool:
+    return any(arch in target for arch in ("x86_64", "amd64", "i386", "i686"))
+
+
 def clang_target_triple(clang_exe: Path) -> str:
     proc = subprocess.run(
         [str(clang_exe), "-dumpmachine"],
@@ -495,6 +500,14 @@ def clang_exe() -> Path:
     clang = find_clang()
     if clang is None:
         pytest.skip("clang not found in PATH; semantic parity tests require an external compiler")
+
+    target = clang_target_triple(clang)
+    if sys.platform == "darwin" and not is_x86_target(target):
+        pytest.skip(
+            "semantic parity tests execute generated native code and are currently "
+            f"skipped on non-x86 macOS targets (got {target or 'unknown'})"
+        )
+
     return clang
 
 
@@ -537,7 +550,7 @@ def test_ollvm_obf_semantic_preservation(
 ) -> None:
     if case.clang_flags:
         target = clang_target_triple(clang_exe)
-        if not any(arch in target for arch in ("x86_64", "amd64", "i386", "i686")):
+        if not is_x86_target(target):
             pytest.skip(f"{case.name} requires an x86 clang target (got {target or 'unknown'})")
 
     input_path = tmp_path / "input.ll"
diff --git a/tools/ci/install_llvm.py b/tools/ci/install_llvm.py
index e395e88..29da066 100644
--- a/tools/ci/install_llvm.py
+++ b/tools/ci/install_llvm.py
@@ -44,6 +44,11 @@ def parse_args() -> argparse.Namespace:
         type=Path,
         help="Destination LLVM root directory.",
     )
+    parser.add_argument(
+        "--prefix-file",
+        type=Path,
+        help="Optional .llvm-prefix file to write with the installed LLVM root.",
+    )
     return parser.parse_args()
 
 
@@ -133,8 +138,15 @@ def main() -> int:
         llvm_root = find_llvm_root(extract_dir)
         install_tree(llvm_root, args.dest)
 
-    print(f"Installed LLVM to {args.dest}", flush=True)
-    llvm_config = args.dest / "bin" / ("llvm-config.exe" if os.name == "nt" else "llvm-config")
+    installed_root = args.dest.resolve()
+    installed_root_for_cmake = installed_root.as_posix()
+    print(f"Installed LLVM to {installed_root}", flush=True)
+    if args.prefix_file is not None:
+        args.prefix_file.parent.mkdir(parents=True, exist_ok=True)
+        args.prefix_file.write_text(installed_root_for_cmake + "\n", encoding="utf-8")
+        print(f"Wrote LLVM prefix file: {args.prefix_file}", flush=True)
+
+    llvm_config = installed_root / "bin" / ("llvm-config.exe" if os.name == "nt" else "llvm-config")
     if llvm_config.exists():
         version = subprocess.check_output([str(llvm_config), "--version"], text=True).strip()
         print(f"LLVM version: {version}", flush=True)