OrderUpdated arrived before OrderCreated

• The order search index shows orders with a status but no items, and some orders are missing entirely.
• The indexer’s error rate went from 0 to ~4% ("order 5510 not found"); the dead-letter topic is filling at 60 msg/min.
• Consumer lag is near zero — the consumers are keeping up.
• It started at 10:55, right after order-svc deployed a change titled "spread producer load across partitions".

# order-indexer consumer log (group=indexer, 6 consumers, topic orders: 12 partitions)
11:02:44.120  p7   off=88213  OrderUpdated  order=5510 status=PAID       → ERROR order 5510 not found → DLQ
11:02:44.131  p2   off=91004  OrderCreated  order=5510 items=3
11:02:44.140  p11  off=87730  OrderUpdated  order=5510 status=CONFIRMED
11:02:44.152  p7   off=88214  OrderUpdated  order=6120 status=PAID       → ok (6120 created 40 s ago)

# order-svc producer diff, deployed 10:55
- await producer.send({ topic: 'orders', messages: [{ key: String(order.id), value }] })
+ await producer.send({ topic: 'orders', messages: [{ key: null, value }] })   // round-robin partitioner

# partition skew before the change (bytes/s, 12 partitions): max/mean = 1.1