test(pairing): cover _PENDING_USER_TURN_KEY cleanup and None allow_from

- Assert pending_user_turn is cleared from session metadata after
  shortcut commands (e.g. /help) in test_auto_compact.py.
- Add test for None allow_from / allowFrom values in
  test_base_channel.py to prevent TypeError regressions.

tests/agent/test_auto_compact.py

@@ -434,6 +434,7 @@ class TestAutoCompactIdleDetection:
         assert session_after.messages[0].get("_command") is True
         assert session_after.messages[1]["role"] == "assistant"
         assert session_after.messages[1].get("_command") is True
+        assert AgentLoop._PENDING_USER_TURN_KEY not in session_after.metadata
         await loop.close_mcp()
 
     @pytest.mark.asyncio