feat: prepare ARR for controlled public deployment

database/003_finance_zero_night_records.down.sql

@@ -0,0 +1,36 @@
+-- DESTRUCTIVE rollback draft for migration 003.
+-- Do not execute while a retained same-day/zero-night Finance record exists.
+-- Target database: booking_test.
+
+BEGIN;
+
+DO $$
+BEGIN
+    IF EXISTS (
+        SELECT 1
+        FROM finance.daily_records
+        WHERE arrival IS NOT NULL
+          AND departure = arrival
+          AND nights = 0
+    ) THEN
+        RAISE EXCEPTION
+            'remove or migrate same-day zero-night records before rolling back migration 003';
+    END IF;
+END;
+$$;
+
+ALTER TABLE finance.daily_records
+    DROP CONSTRAINT daily_records_dates_and_nights_valid;
+
+ALTER TABLE finance.daily_records
+    ADD CONSTRAINT daily_records_dates_and_nights_valid CHECK (
+        arrival IS NULL
+        OR departure IS NULL
+        OR nights IS NULL
+        OR (
+            departure > arrival
+            AND nights = departure - arrival
+        )
+    );
+
+COMMIT;