DC-NODE-26

Decision / durable reconciliation (rung-2). After any applied receive decision, the chain_selector orchestrator's selector.current_tip EQUALS the durable ChainDb::tip (and the orchestrator chain_dep equals the durable PraosChainDepState). The in-memory decision state never diverges from the persisted authority: the orchestrator decides, the durable lockstep path applies, and the two are reconciled every decision. No applied decision leaves the selector ahead of, behind, or forked from the durable spine.