Add Supertrend and VWAP strategies plus a short-side example

- New indicators: vwap (rolling/cumulative) and supertrend (line + direction),
  exposed on StrategyContext.
- New strategies: supertrend (flip-based, optional shorts), vwap_reversion
  (mean reversion below a rolling VWAP) and ema_cross_short (short-side
  example, mirroring the long EMA cross). 10 strategies total.
- Adds indicator and strategy tests; smoke-tested all three on live BTC/USDT
  5m data.

backend/app/engine/strategies/base.py

@@ -5,7 +5,17 @@ from collections.abc import Sequence
 from dataclasses import dataclass
 from typing import Any, ClassVar, Literal, Protocol
 
-from app.engine.indicators import atr, ema, macd, roc, rolling_std, rsi, sma
+from app.engine.indicators import (
+    atr,
+    ema,
+    macd,
+    roc,
+    rolling_std,
+    rsi,
+    sma,
+    supertrend,
+    vwap,
+)
 from app.models import PositionSide
 from app.schemas import Candle, ParamSpec, StrategyOut
 
@@ -116,6 +126,15 @@ class StrategyContext:
     def roc(self, period: int = 10) -> float | None:
         return roc(self.closes, period)[-1]
 
+    def vwap(self, period: int | None = None) -> float | None:
+        return vwap(self._candles, period)[-1]
+
+    def supertrend(
+        self, period: int = 10, multiplier: float = 3.0
+    ) -> tuple[float | None, bool | None]:
+        line, up = supertrend(self._candles, period, multiplier)
+        return line[-1], up[-1]
+
     # --- order intents ------------------------------------------------
     def enter_long(
         self,

backend/app/engine/strategies/ema_cross_short.py

@@ -0,0 +1,70 @@
+from __future__ import annotations
+
+from typing import ClassVar
+
+from app.engine.indicators import atr, ema
+from app.engine.strategies.base import Strategy, StrategyContext, register
+from app.models import PositionSide
+
+
+@register
+class EmaCrossShort(Strategy):
+    """Short-side example: sell EMA cross-downs, cover on cross-up."""
+
+    key: ClassVar[str] = "ema_cross_short"
+    name: ClassVar[str] = "EMA Crossover (short)"
+    description: ClassVar[str] = (
+        "Open a short when the fast EMA crosses below the slow EMA and cover when "
+        "it crosses back above. Demonstrates short trades; optional ATR stop."
+    )
+    default_params: ClassVar[dict] = {
+        "fast": 9,
+        "slow": 21,
+        "atr_period": 14,
+        "atr_stop_mult": 2.0,
+        "size": 1.0,
+    }
+    param_help: ClassVar[dict] = {
+        "fast": "Fast EMA period",
+        "slow": "Slow EMA period",
+        "atr_period": "ATR lookback for the stop",
+        "atr_stop_mult": "Stop distance in ATRs (0 disables)",
+        "size": "Fraction of equity per short",
+    }
+    param_bounds: ClassVar[dict] = {
+        "fast": (2, 100),
+        "slow": (3, 300),
+        "atr_stop_mult": (0.0, 10.0),
+        "size": (0.01, 1.0),
+    }
+
+    def on_candle(self, ctx: StrategyContext) -> None:
+        fast_period = int(self.params["fast"])
+        slow_period = int(self.params["slow"])
+        if len(ctx.closes) < slow_period + 2:
+            return
+
+        fast = ema(ctx.closes, fast_period)
+        slow = ema(ctx.closes, slow_period)
+        f_prev, f_now = fast[-2], fast[-1]
+        s_prev, s_now = slow[-2], slow[-1]
+        if None in (f_prev, f_now, s_prev, s_now):
+            return
+
+        crossed_down = f_prev >= s_prev and f_now < s_now
+        crossed_up = f_prev <= s_prev and f_now > s_now
+
+        if ctx.is_flat and crossed_down:
+            stop = None
+            mult = float(self.params["atr_stop_mult"])
+            if mult > 0:
+                atr_value = atr(ctx.candles, int(self.params["atr_period"]))[-1]
+                if atr_value:
+                    stop = ctx.price + mult * atr_value
+            ctx.enter_short(
+                size=float(self.params["size"]),
+                stop_loss=stop,
+                reason="EMA cross down",
+            )
+        elif ctx.side == PositionSide.SHORT and crossed_up:
+            ctx.close(reason="EMA cross up")

backend/app/engine/strategies/supertrend.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+from typing import ClassVar
+
+from app.engine.indicators import supertrend as supertrend_series
+from app.engine.strategies.base import Strategy, StrategyContext, register
+from app.models import PositionSide
+
+
+@register
+class Supertrend(Strategy):
+    """Trend following on the Supertrend indicator, long or short."""
+
+    key: ClassVar[str] = "supertrend"
+    name: ClassVar[str] = "Supertrend"
+    description: ClassVar[str] = (
+        "Go long when Supertrend flips to an uptrend and short when it flips to "
+        "a downtrend. Uses the Supertrend line as a stop."
+    )
+    default_params: ClassVar[dict] = {
+        "period": 10,
+        "multiplier": 3.0,
+        "allow_shorts": False,
+        "size": 1.0,
+    }
+    param_help: ClassVar[dict] = {
+        "period": "ATR period for the Supertrend bands",
+        "multiplier": "ATR multiplier (band width)",
+        "allow_shorts": "Also take short trades in downtrends",
+        "size": "Fraction of equity per trade",
+    }
+    param_bounds: ClassVar[dict] = {
+        "period": (2, 100),
+        "multiplier": (0.5, 10.0),
+        "size": (0.01, 1.0),
+    }
+
+    def on_candle(self, ctx: StrategyContext) -> None:
+        period = int(self.params["period"])
+        multiplier = float(self.params["multiplier"])
+        if len(ctx.candles) < period + 2:
+            return
+
+        line_series, up_series = supertrend_series(ctx.candles, period, multiplier)
+        line, up = line_series[-1], up_series[-1]
+        prev_up = up_series[-2]
+        if line is None or up is None or prev_up is None:
+            return
+
+        allow_shorts = bool(self.params.get("allow_shorts", False))
+        size = float(self.params["size"])
+
+        if ctx.side == PositionSide.LONG and not up:
+            ctx.close(reason="Supertrend turned down")
+            return
+        if ctx.side == PositionSide.SHORT and up:
+            ctx.close(reason="Supertrend turned up")
+            return
+
+        if ctx.is_flat and up and not prev_up:
+            ctx.enter_long(size=size, stop_loss=line, reason="Supertrend flipped up")
+        elif ctx.is_flat and allow_shorts and not up and prev_up:
+            ctx.enter_short(size=size, stop_loss=line, reason="Supertrend flipped down")

backend/app/engine/strategies/vwap_reversion.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+from typing import ClassVar
+
+from app.engine.strategies.base import Strategy, StrategyContext, register
+from app.models import PositionSide
+
+
+@register
+class VwapReversion(Strategy):
+    """Mean reversion around VWAP, long-only."""
+
+    key: ClassVar[str] = "vwap_reversion"
+    name: ClassVar[str] = "VWAP Reversion"
+    description: ClassVar[str] = (
+        "Open long when price falls this far below a rolling VWAP and exit when "
+        "it returns to VWAP. Optional ATR stop."
+    )
+    default_params: ClassVar[dict] = {
+        "period": 20,
+        "deviation_pct": 0.005,
+        "atr_period": 14,
+        "atr_stop_mult": 2.0,
+        "size": 1.0,
+    }
+    param_help: ClassVar[dict] = {
+        "period": "Rolling VWAP window in bars",
+        "deviation_pct": "Entry distance below VWAP (0.005 = 0.5%)",
+        "atr_period": "ATR lookback for the stop",
+        "atr_stop_mult": "Stop distance in ATRs (0 disables)",
+        "size": "Fraction of equity per trade",
+    }
+    param_bounds: ClassVar[dict] = {
+        "period": (2, 200),
+        "deviation_pct": (0.0, 0.2),
+        "atr_stop_mult": (0.0, 10.0),
+        "size": (0.01, 1.0),
+    }
+
+    def on_candle(self, ctx: StrategyContext) -> None:
+        period = int(self.params["period"])
+        if len(ctx.candles) < period + 1:
+            return
+        reference = ctx.vwap(period)
+        if reference is None or reference <= 0:
+            return
+
+        threshold = reference * (1 - float(self.params["deviation_pct"]))
+
+        if ctx.is_flat and ctx.price < threshold:
+            stop = None
+            mult = float(self.params["atr_stop_mult"])
+            if mult > 0:
+                atr_value = ctx.atr(int(self.params["atr_period"]))
+                if atr_value:
+                    stop = ctx.price - mult * atr_value
+            ctx.enter_long(
+                size=float(self.params["size"]),
+                stop_loss=stop,
+                reason="price below VWAP band",
+            )
+        elif ctx.side == PositionSide.LONG and ctx.price >= reference:
+            ctx.close(reason="price returned to VWAP")