Source: MIZOKI audit 2026-09-06 (pinned fc8b03f9) → work-order backlog 2026-09-08 (docs/audits/AUDIT_WORK_ORDERS_2026-09-08.md). Findings are hypotheses until reproduced on current main (WO-00).

Finding: $40 refund doubled to $80 under concurrency/retry; refund before order lost; two flat fees overwrote each other; changed orders kept stale COGS [R9]. Files: services/net-yield/returns_adjustment.py, bq.py, cost_config.py; tests test_order_economics.py, test_bq.py. Fix: durable unique event ledger keyed by provider event ID; atomic transitions or deterministic materialization; unmatched refunds retained and re-matched; versioned recompute on order change; fees keyed by (tenant, fee_type). Acceptance: against a real test DB: duplicate refund delivery → one entry; refund-before-order → matched later; crash-and-retry → idempotent; two fee types → both kept; order change → COGS recomputed. Depends on: WO-08.