Top strikes by volume / open-interest ratio — institutional positioning signal.

    Use this when the user asks "any unusual options activity on X?", "where
    is the smart money positioned on NVDA before earnings?", or wants a
    V/OI screener for a ticker. A V/OI ratio > 1 means today's volume already
    exceeds standing open interest, which classically flags fresh institutional
    positioning on a specific strike in a specific direction (call vs put).

    Scans the soonest few expirations, filters out illiquid strikes (under
    `min_volume`), and returns the top-N sorted by V/OI descending. Also
    returns aggregate call vs put volume so Claude can comment on the
    overall directional bias.

    Args:
        symbol: US stock symbol — AAPL, NVDA, TSLA, SPY, META, etc.
        top_n: How many strikes to return. Default 10.
        min_volume: Filter floor for today's volume — prevents noise from
            illiquid strikes with high V/OI ratios. Default 100.
        expiries: Number of soonest expirations to scan. Default 4
            (typically covers ~1 month of weeklies + monthlies).

    Returns:
        - underlying_price
        - expiries_scanned (list of YYYY-MM-DD)
        - total_call_volume, total_put_volume, put_call_volume_ratio
        - unusual: list of top-N contracts sorted by V/OI desc, each with
          {strike, side (call|put), expiration, volume, open_interest,
          v_oi_ratio, last_price, implied_volatility, in_the_money,
          strike_vs_spot_pct (moneyness)}