# Two saveAll() calls released at the same instant

seeded with u0, a0; two writers add from-A and from-B; both saveAll() calls start together
The outcome differs from run to run, so the exact count is not printed here. Across repeated runs on
PostgreSQL 16 (READ COMMITTED) it is one of two things, and never the 4 messages that were sent:
  3 messages  -> one writer's message is gone
  6 messages  -> both transactions inserted, history is duplicated, sequence_id values collide