币本位买币改为按最大可开张数×权利金×可配缓冲，不全额兑换USDT

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/options/options_margin_mode_lib.py

@@ -134,6 +134,156 @@ def compute_coin_budget_usdt(
     }
 
 
+def normalize_coin_spot_buy_buffer(raw: Any = None) -> float:
+    """
+    现货买入相对权利金的倍数缓冲.
+    env OKX_OPTIONS_COIN_SPOT_BUY_BUFFER 默认 1.10(=多买 10%).
+    也可写 0.10 表示 +10%.
+    """
+    if raw is None:
+        v = _env_float("OKX_OPTIONS_COIN_SPOT_BUY_BUFFER", 1.10)
+    else:
+        try:
+            v = float(raw)
+        except (TypeError, ValueError):
+            v = 1.10
+    if v <= 0:
+        return 1.10
+    if v < 1.0:
+        return 1.0 + v
+    return v
+
+
+def plan_coin_open_by_budget(
+    *,
+    quote_per_unit: float,
+    ct_mult: float,
+    min_sz: int,
+    budget_usdt: float,
+    index_px: float,
+    ask_sz: float | None = None,
+    spot_buy_buffer: float | None = None,
+    target_sheets: int | None = None,
+) -> dict[str, Any]:
+    """
+    先按预算/卖一估最大可开张数,再按「权利金 × 现货缓冲」算应买现货 USDT.
+    不全额把预算换成币.
+    """
+    import math
+
+    from lib.exchange.okx_options_lib import cap_option_buy_sheets_to_ask_depth
+
+    ask = float(quote_per_unit or 0)
+    mult = float(ct_mult or 0.01)
+    need = max(1, int(min_sz or 1))
+    budget = max(0.0, float(budget_usdt or 0))
+    idx = float(index_px or 0)
+    buf = normalize_coin_spot_buy_buffer(spot_buy_buffer)
+    if ask <= 0 or mult <= 0:
+        return {"ok": False, "msg": "卖一价无效", "sheets": 0, "buy_usdt": 0.0}
+    if idx <= 0:
+        return {"ok": False, "msg": "缺少指数价,无法估算买币 USDT", "sheets": 0, "buy_usdt": 0.0}
+    if budget <= 0:
+        return {"ok": False, "msg": "USDT 预算无效", "sheets": 0, "buy_usdt": 0.0}
+
+    per_sheet_coin = ask * mult
+    # 每张开仓需买的币(含缓冲)及其约合 USDT
+    per_sheet_buy_coin = per_sheet_coin * buf
+    per_sheet_usdt = per_sheet_buy_coin * idx
+    if per_sheet_usdt <= 0:
+        return {"ok": False, "msg": "无法计算单张买币成本", "sheets": 0, "buy_usdt": 0.0}
+
+    max_by_budget = int(math.floor((budget / per_sheet_usdt) + 1e-12))
+    if target_sheets is not None:
+        try:
+            want = int(target_sheets)
+        except (TypeError, ValueError):
+            want = 0
+        if want < need:
+            return {
+                "ok": False,
+                "msg": f"指定张数无效(需≥{need})",
+                "sheets": 0,
+                "buy_usdt": 0.0,
+                "max_by_budget": max_by_budget,
+            }
+        sheets = min(want, max_by_budget)
+        if sheets < want:
+            return {
+                "ok": False,
+                "msg": (
+                    f"预算约可开 {max_by_budget} 张(含现货缓冲×{buf:g}),"
+                    f"不足指定 {want} 张"
+                ),
+                "sheets": 0,
+                "buy_usdt": 0.0,
+                "max_by_budget": max_by_budget,
+                "spot_buy_buffer": buf,
+            }
+    else:
+        sheets = max_by_budget
+
+    capped, cap_msg = cap_option_buy_sheets_to_ask_depth(sheets, ask_sz, min_sz=need)
+    ask_depth_capped = False
+    if capped is None:
+        return {
+            "ok": False,
+            "msg": cap_msg or "卖一深度不足",
+            "sheets": 0,
+            "buy_usdt": 0.0,
+            "spot_buy_buffer": buf,
+        }
+    if int(capped) < sheets:
+        sheets = int(capped)
+        ask_depth_capped = True
+
+    if sheets < need:
+        return {
+            "ok": False,
+            "msg": (
+                f"预算不足,无法买入 {need} 张"
+                f"(单张约需 {per_sheet_usdt:.4f} USDT,含现货缓冲×{buf:g})"
+            ),
+            "sheets": sheets,
+            "buy_usdt": 0.0,
+            "per_sheet_usdt": round(per_sheet_usdt, 8),
+            "spot_buy_buffer": buf,
+            "max_by_budget": max_by_budget,
+        }
+
+    premium_coin = sheets * per_sheet_coin
+    buy_coin = premium_coin * buf
+    buy_usdt = min(budget, buy_coin * idx)
+    # 再保险:向下对齐,避免浮点导致略超预算
+    buy_usdt = min(budget, round(buy_usdt, 8))
+    out = {
+        "ok": True,
+        "msg": "" if not ask_depth_capped else (cap_msg or f"已按卖一深度限制为 {sheets} 张"),
+        "sheets": sheets,
+        "eth_amount": round(sheets * mult, 8),
+        "coin_premium": round(premium_coin, 8),
+        "total_premium": round(premium_coin, 8),
+        "per_sheet_coin": per_sheet_coin,
+        "buy_coin": round(buy_coin, 8),
+        "buy_usdt": round(buy_usdt, 8),
+        "budget_usdt": round(budget, 8),
+        "spot_buy_buffer": buf,
+        "index_px": idx,
+        "max_by_budget": max_by_budget,
+        "ask_depth_capped": ask_depth_capped,
+        "est_note": (
+            f"按最大可开 {sheets} 张×卖一权利金×现货缓冲{buf:g}估买币;"
+            f"不全额兑换预算"
+        ),
+    }
+    if target_sheets is not None:
+        out["est_note"] = (
+            f"指定 {sheets} 张×卖一权利金×现货缓冲{buf:g}估买币;不全额兑换"
+        )
+        out["target_sheets"] = int(target_sheets)
+    return out
+
+
 def calc_sheets_from_coin_balance(
     *,
     quote_per_unit: float,