The cost-tracking plan that survived a three-round panel
A ~150-LOC plan to unify cost tracking — one ledger table, FK-enforced bucket enum, paired-write RPC. The panel shredded v1 as architecturally off: cost_bucket-as-column was the wrong shape; the right shape is a sibling ledger. By v3 the plan had absorbed atomic RPCs, a canonical union view, and an FK-to-lookup-table design.