0029: rescope uq_expense_source_order for per-shipment bridge rows

Split-shipment orders are charged per shipment; the spine bridge now
writes one row per shipment sharing (source, order_reference). Meal-lane
idempotency semantics unchanged (index scope excludes only
source='order-bridge'); bridge rows get their own unique index on
(source, source_message_id). Applied 2026-08-10.

prisma/migrations/0029_bridge_shipment_rows/migration.sql

@@ -0,0 +1,25 @@
+-- 0029: let the spine bridge write one row PER SHIPMENT of a split order.
+--
+-- An Amazon order that ships in two boxes is charged per shipment, so its
+-- order_total matches no statement line — the bridge (ingestion-engine
+-- jobs/order_transaction_bridge.py) matches each shipment's own amount and
+-- items instead. Those rows share (source='order-bridge', order_reference),
+-- which uq_expense_source_order forbade.
+--
+-- The index exists as the MEAL lane's idempotency key (0018 I7), and that
+-- lane's semantics are untouched: the scope simply excludes bridge rows,
+-- whose idempotency key is source_message_id (<entity_key> for whole-order
+-- rows, <entity_key>#f<fact_id> per shipment) — now enforced with its own
+-- unique index instead of by convention. No app code does ON CONFLICT
+-- against either index; ingest idempotency is SELECT-based
+-- (lib/order-ingestion.ts).
+
+DROP INDEX IF EXISTS uq_expense_source_order;
+
+CREATE UNIQUE INDEX uq_expense_source_order
+  ON expense_metadata (source, order_reference)
+  WHERE order_reference IS NOT NULL AND source <> 'order-bridge';
+
+CREATE UNIQUE INDEX uq_expense_bridge_message
+  ON expense_metadata (source, source_message_id)
+  WHERE source = 'order-bridge';