Handle explicit pre-1 package home without HOME

scripts/pre1_package_execution.py

@@ -343,9 +343,8 @@ def validate_binding_context(value: dict, context: dict) -> None:
 
 def prepared_package_home() -> Path:
     """Keep the immutable preparation boundary separate from per-case HOME."""
-    return safe_path(
-        Path(os.environ.get("IICP_PRE1_PREPARED_PACKAGE_HOME", os.environ["HOME"]))
-    )
+    value = os.environ.get("IICP_PRE1_PREPARED_PACKAGE_HOME")
+    return safe_path(Path(value if value is not None else os.environ["HOME"]))
 
 
 def validate_binding(value: dict, context: dict, artifact: Path, root: Path,

scripts/test_pre1_prepared_home.py

@@ -2,10 +2,11 @@
 import ast
 import json
 import os
-from pathlib import Path
 import tempfile
 import unittest
+from pathlib import Path
 from unittest.mock import patch
+
 import pre1_package_execution as adapter
 
 
@@ -36,6 +37,11 @@ def test_execution_home_does_not_replace_preparation_owner(self):
             with self.assertRaises(ValueError):
                 adapter.validate_workspace_boundary(workspace, self.case, installed, source)
 
+    def test_explicit_preparation_owner_does_not_require_home(self):
+        env = {"IICP_PRE1_PREPARED_PACKAGE_HOME": str(self.prepared)}
+        with patch.dict(os.environ, env, clear=True):
+            self.assertEqual(adapter.prepared_package_home(), self.prepared)
+
     def test_wrong_explicit_preparation_boundary_is_rejected(self):
         workspace = self.prepared / "workspace"
         installed = workspace / "payload"