feat: add voice co-creation session skeleton

backend/tests/conftest.py

@@ -187,6 +187,18 @@ def isolated_story_audio_cache(tmp_path, monkeypatch):
     yield
 
 
+@pytest.fixture(autouse=True)
+def isolated_voice_session_storage(tmp_path, monkeypatch):
+    """Use an isolated directory for voice session assets."""
+
+    monkeypatch.setattr(
+        settings,
+        "voice_session_storage_dir",
+        str(tmp_path / "voice_sessions"),
+    )
+    yield
+
+
 @pytest.fixture
 def mock_text_provider():
     """Mock text generation."""