rack：刷机模式界面与事件；事件 21 新增 254「断电自动退出」

- 单板页「更多 → 刷机模式（1 小时）/ 加钟 30 分钟」，chg>0 时蓝色「刷机模式 · 充电中」、FLT 显示为「反向阻断」
- 协议白名单 flash_mode；事件 21 命名：开 / 手动关 / 到期 / 加钟 / 断电自动退出
- ⚠️ 254 带 0x80 位，必须先于「加钟」判断，否则显示成「加钟 126 分钟」

48 例全绿，已部署。

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

rack/backend/prrack/simboard.py

@@ -30,6 +30,7 @@ class SimRail:
         self.busy_until = 0
         self.act = "idle"
         self.pending: Optional[str] = None  # 序列结束时要做的事
+        self.chg_until = 0  # 刷机模式截止（模拟时钟 ms），0 = 没开
 
 
 class SimBoard:
@@ -132,7 +133,9 @@ class SimBoard:
             rails.append({"r": r.rail, "pr": r.present, "en": r.en, "vb": r.vb, "set": r.set_mv,
                           "mv": (r.set_mv if r.en else 0) if ok else None,
                           "ua": r.ua if ok else None, "pg": r.en if ok else None,
-                          "flt": False if ok else None, "st": r.act, "res": "-"})
+                          "flt": False if ok else None,
+                          "chg": max(0, (r.chg_until - self.now + 999) // 1000) if r.chg_until else 0,
+                          "st": r.act, "res": "-"})
         return {"ok": True, "fw": self.fw, "up": self.up_ms, "in": {"mv": 12030, "ua": 1500000},
                 "rails": rails, "temp": [35000, 36500],
                 "fan": {"duty": max(300, self.fan_floor), "floor": self.fan_floor, "en": True,
@@ -231,7 +234,31 @@ class SimBoard:
             r.en = req["on"]
             if not r.en:
                 r.vb = False
+                if r.chg_until > self.now:
+                    r.chg_until = 0
+                    self._ev(rail, 21, 0)
             return {"ok": True}
+        if cmd == "flash_mode":  # 固件 chgmode.h 的规则：最多 2 路、关着电不许开、关电一并退出
+            if "add" in req:  # 0.1.6 加钟：只给开着的加，剩余截断到 120 分钟
+                if r.chg_until <= self.now:
+                    return {"ok": False, "err": "state"}
+                r.chg_until = min(r.chg_until + req["add"] * 60000, self.now + 120 * 60000)
+                self._ev(rail, 21, 0x80 | req["add"])
+                return {"ok": True, "left": (r.chg_until - self.now + 999) // 1000}
+            if not req["on"]:
+                if r.chg_until > self.now:
+                    self._ev(rail, 21, 0)
+                r.chg_until = 0
+                return {"ok": True, "left": 0}
+            if not r.en:
+                return {"ok": False, "err": "state"}
+            active = sum(1 for x in self.rails if x is not r and x.chg_until > self.now)
+            if active >= 2:
+                return {"ok": False, "err": "state"}
+            m = req.get("min", 60)
+            r.chg_until = self.now + m * 60000
+            self._ev(rail, 21, m)
+            return {"ok": True, "left": m * 60}
         if cmd == "set_voltage":
             r.set_mv = req["mv"]
             return {"ok": True, "set": r.set_mv}