fix: preserve snapshot compatibility and loan fallback

tests/test_issue_12_regressions.py

@@ -453,6 +453,58 @@ def test_legacy_snapshot_rows_do_not_override_live_authority_or_claim_closed(tmp
     assert report["legacy_snapshot_row_count"] == 1
 
 
+def test_snapshot_public_api_preserves_legacy_db_path_position(tmp_path):
+    path = str(tmp_path / "ledger.sqlite3")
+    preview = service.preview_asset_snapshot_close("2026-06-30", path)
+    closed = service.close_asset_snapshot("2026-06-30", "", "", "", path)
+    report = service.get_asset_snapshot_report("2026-06-30", path)
+    assert preview["success"] is True
+    assert closed["success"] is True
+    assert report["success"] is True
+    assert report["is_closed_snapshot"] is True
+
+
+def test_legacy_snapshot_requires_explicit_correction_before_new_close(tmp_path):
+    path = str(tmp_path / "ledger.sqlite3")
+    service.create_asset_snapshot(
+        "2026-06-30", "account", "legacy", "legacy", 999, "cash", db_path=path,
+    )
+    close = service.close_asset_snapshot("2026-06-30", db_path=path)
+    report = service.get_asset_snapshot_report("2026-06-30", db_path=path)
+    assert close["success"] is False
+    assert close["error_code"] == "legacy_snapshot_correction_required"
+    assert report["source"] == "legacy_asset_snapshots"
+    assert report["net_worth"] == 999
+    assert report["is_closed_snapshot"] is False
+
+
+def test_loan_balance_fallback_with_representative_definition_is_liability(tmp_path):
+    path = str(tmp_path / "ledger.sqlite3")
+    account = service.create_ledger_account("대출", type="loan", db_path=path)["account"]["id"]
+    recorded = service.register_account_valuation(
+        account, "2026-06-30", 100, valuation_kind="balance",
+        representative_liability_definition="principal_only",
+        verification_status="verified", db_path=path,
+    )
+    report = service.get_asset_snapshot_report("2026-06-30", db_path=path)
+    assert recorded["success"] is True
+    assert report["total_assets"] == 0
+    assert report["total_liabilities"] == 100
+    assert report["net_worth"] == -100
+
+
+def test_loan_balance_fallback_rejects_unknown_representative_definition(tmp_path):
+    path = str(tmp_path / "ledger.sqlite3")
+    account = service.create_ledger_account("대출", type="loan", db_path=path)["account"]["id"]
+    recorded = service.register_account_valuation(
+        account, "2026-06-30", 100, valuation_kind="balance",
+        representative_liability_definition="outstanding_principal",
+        verification_status="verified", db_path=path,
+    )
+    assert recorded["success"] is False
+    assert recorded["error_code"] == "validation_error"
+
+
 def test_account_write_rolls_back_when_conn_level_candidate_write_fails(tmp_path, monkeypatch):
     path = str(tmp_path / "ledger.sqlite3")
     import jarca_ledger_mcp.application.accounts_write_services as writes