Spot token price in USD on Base, read from BaseSwap, SushiSwap and Uniswap v3 pools at call time. Returns priceUsd, the routed pair, backing liquidityUsd, confidence and blockNumber. Requires ?symbol=TICKER (e.g. WETH) or ?token=0xADDRESS. Errors: 400 missing_symbol|unknown_token, 404 no_reliable_price when pools are too thin, 502 upstream_read_failed. Depth is /liquidity; a size-aware quote is /slippage. Chain-pinned; bare /price = BSC.