feat: wrap LLM clients with TrackedLLMClient in LLMFactory

backend/tests/observability/test_llm_factory_tracking.py

@@ -0,0 +1,44 @@
+"""Verifies get_llm_client() returns a usage-tracked client end to end."""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from app.services.llm.llm_factory import LLMFactory, get_llm_client
+from app.services.llm.tracked_client import TrackedLLMClient
+from app.shared.model_usage_tracker import get_model_usage_tracker
+
+
+@pytest.fixture(autouse=True)
+def _reset_singletons():
+    """Clear the two process-wide singletons this test touches, before and after.
+
+    LLMFactory._global_instances and get_model_usage_tracker() both persist
+    for the life of the process; without this fixture, tests would leak
+    cached clients/usage data into each other and become order-dependent.
+    """
+    LLMFactory._global_instances.clear()
+    get_model_usage_tracker().snapshot()  # no-op read, just documents intent
+    get_model_usage_tracker()._entries.clear()
+    yield
+    LLMFactory._global_instances.clear()
+    get_model_usage_tracker()._entries.clear()
+
+
+def test_get_llm_client_returns_tracked_client():
+    """get_llm_client() must return a TrackedLLMClient, not the raw provider client."""
+    with patch("app.services.llm.llm_factory.DeepSeekClient") as mock_cls:
+        mock_cls.return_value = MagicMock()
+        client = get_llm_client(provider="deepseek", model="deepseek-v4-flash", api_key="test-key")
+    assert isinstance(client, TrackedLLMClient)
+
+
+def test_get_llm_client_caches_the_tracked_instance():
+    """A second call with the same provider/model must return the same TrackedLLMClient."""
+    with patch("app.services.llm.llm_factory.DeepSeekClient") as mock_cls:
+        mock_cls.return_value = MagicMock()
+        first = get_llm_client(provider="deepseek", model="deepseek-v4-flash", api_key="test-key")
+        second = get_llm_client(provider="deepseek", model="deepseek-v4-flash", api_key="test-key")
+    assert first is second