Fix Review 64 valuation authority regressions

tests/test_import_current_balance_authority.py

@@ -65,6 +65,42 @@ def test_late_import_current_balance_is_authoritative_by_evidence_basis_date(mon
     }
 
 
+def test_empty_balance_with_basis_date_is_rejected_without_mutation_before_import(tmp_path, monkeypatch):
+    path = str(tmp_path / "ledger.sqlite3")
+    account = service.create_ledger_account("KB", institution="KB국민은행", db_path=path)["account"]["id"]
+    before = service.list_ledger_accounts(active_only=False, db_path=path)["accounts"][0]
+    before_valuations = service.list_account_valuations(account, db_path=path)["valuations"]
+
+    rejected = service.update_ledger_account(
+        account,
+        last_balance="",
+        last_balance_basis_date="2026-07-01",
+        db_path=path,
+    )
+
+    after = service.list_ledger_accounts(active_only=False, db_path=path)["accounts"][0]
+    after_valuations = service.list_account_valuations(account, db_path=path)["valuations"]
+    assert rejected["success"] is False
+    assert rejected["error_code"] == "validation_error"
+    assert after == before
+    assert after_valuations == before_valuations
+
+    monkeypatch.setattr(
+        imports_service,
+        "parse_kb_bank_pdf",
+        lambda *_: _parsed(_transaction("2026-06-30", 900, 1), "hash-valid"),
+    )
+    monkeypatch.setattr(imports_service, "now_iso", lambda: "2026-07-02T09:00:00")
+    imported = imports_service.import_kb_bank_pdf("synthetic", "pw", account_id=account, db_path=path)
+
+    current = service.list_ledger_accounts(active_only=False, db_path=path)["accounts"][0]
+    valuations = service.list_account_valuations(account, db_path=path)["valuations"]
+    assert imported["success"] is True
+    assert current["last_balance"] == 900
+    assert current["last_balance_basis_date"] == "2026-06-30"
+    assert {(item["basis_date"], item["amount"]) for item in valuations} == {("2026-06-30", 900)}
+
+
 def test_account_write_sync_timestamp_does_not_infer_balance_basis_or_candidate(tmp_path):
     path = str(tmp_path / "ledger.sqlite3")
     unknown = service.create_ledger_account(