fix(metrics): reset global metrics collector during teardown to avoid test pollution

hindsight-api-slim/hindsight_api/api/http.py

@@ -198,6 +198,7 @@ def FieldWithDefault(default_factory: Callable, **kwargs) -> Any:
     get_metrics_collector,
     initialize_metrics,
     normalize_http_endpoint,
+    reset_metrics_collector,
 )
 from hindsight_api.models import RequestContext
 
@@ -3970,6 +3971,9 @@ async def lifespan(app: FastAPI):
 
         shutdown_tracing()
 
+        # Prevent in-process app instances from leaking a live collector across tests (#3780).
+        reset_metrics_collector()
+
     from hindsight_api import __version__
     from hindsight_api.config import get_config
 

hindsight-api-slim/hindsight_api/metrics.py

@@ -1120,3 +1120,11 @@ def create_metrics_collector() -> MetricsCollector:
     global _metrics_collector
     _metrics_collector = MetricsCollector()
     return _metrics_collector
+
+
+def reset_metrics_collector() -> None:
+    """
+    Reset the global metrics collector back to NoOpMetricsCollector.
+    """
+    global _metrics_collector
+    _metrics_collector = NoOpMetricsCollector()

hindsight-api-slim/tests/conftest.py

@@ -111,6 +111,26 @@ def _cleanup_leaked_span_recorders():
             recorders.remove(recorder)
 
 
+@pytest.fixture(autouse=True)
+def _cleanup_leaked_metrics_collector():
+    """Reset the process-global metrics collector to NoOpMetricsCollector around each test (#3780).
+
+    ``create_metrics_collector()`` (called e.g. during FastAPI app lifespan startup)
+    permanently sets ``_metrics_collector`` to a real ``MetricsCollector``. Without
+    per-test teardown, this leaks across tests in the same pytest-xdist worker.
+    Subsequent provider tests with MagicMock-based usage objects fail with
+    TypeError when ``MetricsCollector.record_llm_call`` performs integer comparisons.
+    """
+    import hindsight_api.metrics as metrics_module
+
+    original_collector = metrics_module._metrics_collector
+    metrics_module._metrics_collector = metrics_module.NoOpMetricsCollector()
+    try:
+        yield
+    finally:
+        metrics_module._metrics_collector = original_collector
+
+
 # Default pg0 instance configuration for tests
 DEFAULT_PG0_INSTANCE_NAME = "hindsight-test"
 DEFAULT_PG0_PORT = int(os.environ.get("HINDSIGHT_TEST_PG_PORT", "5556"))

hindsight-api-slim/tests/test_metrics.py

@@ -12,6 +12,7 @@
     create_metrics_collector,
     initialize_metrics,
     normalize_http_endpoint,
+    reset_metrics_collector,
 )
 
 
@@ -266,21 +267,23 @@ def test_record_operation_includes_bank_id_when_enabled(self):
 
 
 class TestGetMetricsCollector:
-    """Tests for the get_metrics_collector function."""
+    """Tests for the get_metrics_collector and reset_metrics_collector functions."""
 
     def test_returns_noop_by_default(self):
         """Test that get_metrics_collector returns NoOpMetricsCollector by default."""
-        # Reset global state
-        import hindsight_api.metrics as metrics_module
+        collector = get_metrics_collector()
+        assert isinstance(collector, NoOpMetricsCollector)
 
-        original_collector = metrics_module._metrics_collector
+    def test_create_and_reset_metrics_collector(self):
+        """Test creating and resetting the global metrics collector (#3780)."""
+        with patch("hindsight_api.metrics.get_meter") as mock_get_meter:
+            mock_get_meter.return_value = MagicMock()
+            collector = create_metrics_collector()
+            assert isinstance(collector, MetricsCollector)
+            assert get_metrics_collector() is collector
 
-        try:
-            metrics_module._metrics_collector = NoOpMetricsCollector()
-            collector = get_metrics_collector()
-            assert isinstance(collector, NoOpMetricsCollector)
-        finally:
-            metrics_module._metrics_collector = original_collector
+            reset_metrics_collector()
+            assert isinstance(get_metrics_collector(), NoOpMetricsCollector)
 
 
 class TestMetricsCollectorBase: