Implement client cost attribution

tests/test_ledger.py

@@ -1,3 +1,4 @@
+import sqlite3
 from pathlib import Path
 
 import pytest
@@ -36,6 +37,53 @@ def test_ledger_import_skips_unchanged_file(tmp_path: Path):
     assert second.rows_imported == 0
 
 
+def test_ledger_import_preserves_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",
+    )
+    ledger = tmp_path / "ledger.db"
+
+    import_csv(source, "hosteurope", ledger_path=ledger)
+
+    with sqlite3.connect(ledger) as conn:
+        row = conn.execute(
+            "SELECT client_id, application_id, app_instance_id, cost_attribution_key "
+            "FROM ledger_entries"
+        ).fetchone()
+    assert row == (
+        "acme",
+        "portal",
+        "prod-01",
+        "client:acme|app:portal|instance:prod-01",
+    )
+
+
+def test_existing_ledger_schema_is_migrated_additively(tmp_path: Path):
+    ledger = tmp_path / "legacy.db"
+    with sqlite3.connect(ledger) as conn:
+        conn.execute(
+            "CREATE TABLE ledger_entries ("
+            "id INTEGER PRIMARY KEY, source_type TEXT NOT NULL, category TEXT NOT NULL, "
+            "label TEXT NOT NULL, amount REAL NOT NULL, currency TEXT NOT NULL, "
+            "period_month TEXT NOT NULL, incurred_on TEXT, source_path TEXT NOT NULL, "
+            "imported_at TEXT NOT NULL)"
+        )
+
+    monthly_summary(ledger_path=ledger)
+
+    with sqlite3.connect(ledger) as conn:
+        columns = {row[1] for row in conn.execute("PRAGMA table_info(ledger_entries)")}
+    assert {
+        "client_id",
+        "application_id",
+        "app_instance_id",
+        "cost_attribution_key",
+    }.issubset(columns)
+
+
 def test_evaluate_runway_from_ledger(tmp_path: Path):
     ledger = tmp_path / "ledger.db"
     seed_fixture_ledger(ledger_path=ledger, opening_balance=12000.0)
@@ -57,4 +105,4 @@ def test_build_runway_report_and_write_evidence(tmp_path: Path):
         opening_balance=12000.0,
     )
     assert output.exists()
-    assert "runway-dogfood-" in output.name
+    assert "runway-dogfood-" in output.name