diff --git a/tests/test_release_build.py b/tests/test_release_build.py
index 55ce5e7..f9676bc 100644
--- a/tests/test_release_build.py
+++ b/tests/test_release_build.py
@@ -37,7 +37,7 @@ def test_build_is_deterministic_and_clean_installable(self) -> None:
                 manifest["artifact"]["sha256"], hashlib.sha256((first / name).read_bytes()).hexdigest()
             )
             installed = subprocess.run(
-                ["python3", str(INSTALLER), str(first / name), "--skip-tests"],
+                ["python3", str(INSTALLER), str(first / name)],
                 cwd=ROOT,
                 capture_output=True,
                 text=True,
diff --git a/tools/verify_clean_install.py b/tools/verify_clean_install.py
index aaa5633..79f8714 100644
--- a/tools/verify_clean_install.py
+++ b/tools/verify_clean_install.py
@@ -4,6 +4,8 @@
 from __future__ import annotations
 
 import argparse
+import os
+import shutil
 import stat
 import subprocess
 import sys
@@ -28,6 +30,26 @@ def run(*arguments: str, cwd: Path) -> None:
         raise ValueError((result.stdout + result.stderr).strip() or f"command failed: {arguments}")
 
 
+def extract_with_modes(archive: zipfile.ZipFile, destination: Path) -> None:
+    """Extract validated members without following links and restore portable modes."""
+
+    for item in archive.infolist():
+        relative = PurePosixPath(item.filename)
+        target = destination.joinpath(*relative.parts)
+        if item.is_dir():
+            target.mkdir(parents=True, exist_ok=True)
+            continue
+        mode = stat.S_IMODE(item.external_attr >> 16)
+        if mode not in {0o644, 0o755}:
+            raise ValueError(f"release ZIP has an unsupported file mode: {item.filename}")
+        target.parent.mkdir(parents=True, exist_ok=True)
+        with archive.open(item) as source, target.open("wb") as output:
+            shutil.copyfileobj(source, output)
+        os.chmod(target, mode)
+        if stat.S_IMODE(target.stat().st_mode) != mode:
+            raise ValueError(f"could not restore release file mode: {item.filename}")
+
+
 def main() -> int:
     args = parse_args()
     try:
@@ -50,7 +72,7 @@ def main() -> int:
                     raise ValueError("release ZIP contains a symbolic link")
             with tempfile.TemporaryDirectory(prefix="web-plan-execute-install-") as temporary:
                 destination = Path(temporary)
-                archive.extractall(destination)
+                extract_with_modes(archive, destination)
                 skill = destination / "web-plan-execute"
                 run(
                     sys.executable,