Close a routed position across both legs of a market link

Sells the holdings on each leg of an approved market link, at a per-leg floor price derived from that leg's best bid minus slippage_cents (never below 0.01). Holdings are rounded down to the venue's share precision, and a leg with less than 0.01 sellable is skipped. leg_caps is fail-closed: if you send it, a leg with no matching entry is excluded from the close entirely rather than closed in full. Like route-buy, this is a 200 with status: submitting and per-leg error strings; it is gated by ROUTED_EXECUTION_ENABLED. Auth & scope. Requires the mutation gate; per-leg trade:execute and provider checks happen on each child order.