Pre-execution oracle staleness check: direct eth_call to a Chainlink aggregator's latestRoundData(). feed = 0x-address OR alias (eth-usd, btc-usd, usdc-usd). Returns scaled answer, updated_at, staleness vs the feed's real heartbeat, and is_safe_to_use. Call before borrows or oracle-dependent execution. Chains: ethereum, base, arbitrum, optimism.