Implement client cost attribution

tests/test_ingest.py

@@ -1,5 +1,7 @@
 from pathlib import Path
 
+import pytest
+
 from fin_hub.ingest.anthropic import parse_anthropic_billing_csv
 from fin_hub.ingest.cloud import parse_cloud_cost_csv
 from fin_hub.ingest.hosteurope import parse_hosteurope_csv
@@ -25,4 +27,31 @@ def test_parse_hosteurope_csv():
     rows = parse_hosteurope_csv(FIXTURES / "hosteurope.csv")
     assert len(rows) == 2
     assert rows[0].service_id == "dedicated-server-m"
-    assert rows[0].period_month == "2026-06"
+    assert rows[0].period_month == "2026-06"
+
+
+def test_parse_hosteurope_client_attribution(tmp_path: Path):
+    source = tmp_path / "attributed.csv"
+    source.write_text(
+        "product,amount,currency,invoice_date,client_id,application_id,app_instance_id\n"
+        "Managed cluster,42.00,EUR,2026-07-01,acme,portal,prod-01\n",
+        encoding="utf-8",
+    )
+
+    row = parse_hosteurope_csv(source)[0]
+    assert row.client_id == "acme"
+    assert row.application_id == "portal"
+    assert row.app_instance_id == "prod-01"
+    assert row.cost_attribution_key == "client:acme|app:portal|instance:prod-01"
+
+
+def test_parse_hosteurope_rejects_partial_attribution(tmp_path: Path):
+    source = tmp_path / "partial.csv"
+    source.write_text(
+        "product,amount,currency,invoice_date,client_id\n"
+        "Managed cluster,42.00,EUR,2026-07-01,acme\n",
+        encoding="utf-8",
+    )
+
+    with pytest.raises(ValueError, match="must be supplied together"):
+        parse_hosteurope_csv(source)