test: fix platform-specific test failures

- test_auth.py: Update regex to expect "Unsupported platform" instead of
  "Encrypted token decryption" since platform check happens before decryption
- test_file_utils.py: Skip test_atomic_write_permission_denied_parent on
  Windows where chmod doesn't prevent file creation

tests/core/test_auth.py

@@ -937,10 +937,11 @@ class TestTokenValidationEdgeCases:
         valid_token = "enc:0123456789"
 
         # This should pass basic length validation
-        # (will fail later during actual decryption attempt with NotImplementedError)
+        # (will fail later during actual decryption attempt with ValueError)
         # Arrange & Act & Assert
-        # Will fail during platform decryption, not validation
-        with pytest.raises(ValueError, match="Encrypted token decryption"):
+        # Will fail during platform check since is_macos is mocked to False
+        # and platform is not Linux or Windows either
+        with pytest.raises(ValueError, match="Unsupported platform"):
             decrypt_token(valid_token)
 
 

tests/core/test_file_utils.py

@@ -504,13 +504,19 @@ class TestAtomicWriteEdgeCases:
 
     def test_atomic_write_permission_denied_parent(self, tmp_path):
         """Test atomic_write when parent directory is read-only."""
+        import sys
+        import stat
+
+        # Skip on Windows - chmod doesn't prevent file creation
+        if sys.platform == "win32":
+            pytest.skip("Directory read-only doesn't prevent file creation on Windows")
+
         # Create a directory and make it read-only
         ro_dir = tmp_path / "readonly"
         ro_dir.mkdir()
         filepath = ro_dir / "test.txt"
 
-        # Make directory read-only (skip on Windows where chmod may not work)
-        import stat
+        # Make directory read-only (skip on platforms where chmod may not work)
         try:
             ro_dir.chmod(stat.S_IRUSR | stat.S_IXUSR)
         except (OSError, AttributeError):