AssignmentRepository.createAssignment now catches the assignments_one_current_per_ticket unique-violation and retries the whole supersede-then-create transaction (bounded, with jitter) instead of propagating a raw P2002 to the caller. Verified against real Postgres: before this fix, 20 genuinely concurrent assignment attempts on the same ticket reliably threw an unhandled unique-constraint error; after it, exactly one current assignment results every time across 10 repeated runs. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>