feat: add pipeline observability and stats

tests/integration/test_ingestion_api.py

@@ -38,6 +38,35 @@ class FakePublisher:
         )
 
 
+class FakeWorkerStatsClient:
+    async def get_stats(
+        self,
+    ) -> dict[str, Any]:
+        return {
+            "pipeline": {
+                "total_processed": 10,
+                "total_dlq": 2,
+                "in_flight_buffer": 3,
+                "last_flush_at":
+                    "2026-09-20T12:00:00Z",
+            },
+            "breakdown": {
+                "by_service_type": {
+                    "4G_DATA": 10,
+                },
+                "by_radio_access_type": {
+                    "LTE_4G": 10,
+                },
+                "dlq_by_reason": {
+                    "invalid_rat_value": 2,
+                },
+            },
+        }
+
+    async def close(self) -> None:
+        pass
+
+
 @pytest.fixture
 def publisher() -> FakePublisher:
     return FakePublisher()
@@ -49,6 +78,7 @@ def client(
 ):
     app = create_app(
         publisher=publisher,
+        worker_stats_client=FakeWorkerStatsClient(),
     )
 
     with TestClient(app) as test_client:
@@ -226,3 +256,74 @@ def test_kafka_failure_returns_503(
     assert response.status_code == 503
 
     assert response.json()["error"] == "kafka_unavailable"
+
+
+def test_metrics_endpoint(
+    client: TestClient,
+) -> None:
+    response = client.get(
+        "/metrics"
+    )
+
+    assert response.status_code == 200
+
+    assert (
+        "cdr_api_received_total"
+        in response.text
+    )
+
+
+def test_stats_endpoint(
+    client: TestClient,
+) -> None:
+    response = client.get(
+        "/stats"
+    )
+
+    assert response.status_code == 200
+
+    body = response.json()
+
+    assert (
+        body["pipeline"]["total_processed"]
+        == 10
+    )
+
+    assert (
+        body["pipeline"]["total_dlq"]
+        == 2
+    )
+
+    assert (
+        body["pipeline"]["in_flight_buffer"]
+        == 3
+    )
+
+    assert (
+        body["breakdown"]
+        ["by_service_type"]
+        ["4G_DATA"]
+        == 10
+    )
+
+
+def test_successful_request_increments_api_metric(
+    client: TestClient,
+) -> None:
+    response = client.post(
+        "/api/v1/cdr/raw",
+        json=valid_payload(),
+    )
+
+    assert response.status_code == 202
+
+    metrics = client.get(
+        "/metrics"
+    )
+
+    assert (
+        'cdr_api_received_total 1.0'
+        in metrics.text
+    )
+
+