test: add safe environment variable handling in integration tests

Changes:
- Add temporary_home() context manager for safe HOME manipulation
- Handle both Unix (HOME) and Windows (USERPROFILE, HOMEDRIVE, HOMEPATH)
- Update test_org_blocklist_enforcement to use context manager
- Update test_org_allowlist_inheritance to use context manager

Benefits:
- Environment variables always restored, even on exceptions
- Prevents test pollution across test runs
- Cross-platform compatibility (Windows + Unix)

All 9 integration tests passing.

test_security_integration.py

@@ -19,11 +19,56 @@ import asyncio
 import os
 import sys
 import tempfile
+from contextlib import contextmanager
 from pathlib import Path
 
 from security import bash_security_hook
 
 
+@contextmanager
+def temporary_home(home_path):
+    """
+    Context manager to temporarily set HOME (and Windows equivalents).
+
+    Saves original environment variables and restores them on exit,
+    even if an exception occurs.
+
+    Args:
+        home_path: Path to use as temporary home directory
+    """
+    # Save original values for Unix and Windows
+    saved_env = {
+        "HOME": os.environ.get("HOME"),
+        "USERPROFILE": os.environ.get("USERPROFILE"),
+        "HOMEDRIVE": os.environ.get("HOMEDRIVE"),
+        "HOMEPATH": os.environ.get("HOMEPATH"),
+    }
+
+    try:
+        # Set new home directory for both Unix and Windows
+        os.environ["HOME"] = str(home_path)
+        if sys.platform == "win32":
+            os.environ["USERPROFILE"] = str(home_path)
+            # Note: HOMEDRIVE and HOMEPATH are typically set by Windows
+            # but we update them for consistency
+            drive, path = os.path.splitdrive(str(home_path))
+            if drive:
+                os.environ["HOMEDRIVE"] = drive
+                os.environ["HOMEPATH"] = path
+
+        yield
+
+    finally:
+        # Restore all original values
+        for key, value in saved_env.items():
+            if value is None:
+                # Remove if it didn't exist before
+                os.environ.pop(key, None)
+            else:
+                # Restore original value
+                os.environ[key] = value
+
+
 def test_blocked_command_via_hook():
     """Test that hardcoded blocked commands are rejected by the security hook."""
     print("\n" + "=" * 70)
@@ -200,10 +245,8 @@ def test_org_blocklist_enforcement():
 
     with tempfile.TemporaryDirectory() as tmphome:
         with tempfile.TemporaryDirectory() as tmpproject:
-            # Setup fake home directory with org config
-            original_home = os.environ.get("HOME")
-            os.environ["HOME"] = tmphome
-
+            # Use context manager to safely set and restore HOME
+            with temporary_home(tmphome):
                 org_dir = Path(tmphome) / ".autocoder"
                 org_dir.mkdir()
                 (org_dir / "config.yaml").write_text("""version: 1
@@ -233,12 +276,6 @@ commands:
 
                 result = asyncio.run(bash_security_hook(input_data, context=context))
 
-            # Restore HOME
-            if original_home:
-                os.environ["HOME"] = original_home
-            else:
-                del os.environ["HOME"]
-
                 if result.get("decision") == "block":
                     print("✅ PASS: terraform blocked by org config (cannot override)")
                     print(f"   Reason: {result.get('reason', 'N/A')[:80]}...")
@@ -256,10 +293,8 @@ def test_org_allowlist_inheritance():
 
     with tempfile.TemporaryDirectory() as tmphome:
         with tempfile.TemporaryDirectory() as tmpproject:
-            # Setup fake home directory with org config
-            original_home = os.environ.get("HOME")
-            os.environ["HOME"] = tmphome
-
+            # Use context manager to safely set and restore HOME
+            with temporary_home(tmphome):
                 org_dir = Path(tmphome) / ".autocoder"
                 org_dir.mkdir()
                 (org_dir / "config.yaml").write_text("""version: 1
@@ -282,12 +317,6 @@ blocked_commands: []
 
                 result = asyncio.run(bash_security_hook(input_data, context=context))
 
-            # Restore HOME
-            if original_home:
-                os.environ["HOME"] = original_home
-            else:
-                del os.environ["HOME"]
-
                 if result.get("decision") != "block":
                     print("✅ PASS: jq allowed via org config")
                     return True