Spot token price in USD on Polygon PoS, read from QuickSwap, SushiSwap and Uniswap v3 pools at call time. Returns priceUsd, the routed pair, backing liquidityUsd, confidence and blockNumber. Requires ?symbol=TICKER (e.g. WMATIC) 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.