MarketMaker.cc Team
Recherche quantitative et stratégie
Finale of the "Backtests Without Illusions" series. How to build an orchestrator from N strategies on M pairs, implement cascade mode with priority and fallback execution, choose dual_size, and why strategy portfolios cannot be backtested by simply summing PnL.
You've put a strategy through the full pipeline. Monte Carlo bootstrap showed an acceptable 5th percentile. Walk-forward confirmed out-of-sample returns. Funding rates are accounted for, plateau analysis passed. The strategy genuinely works.
But it trades 15% of the time. The remaining 85% your capital sits idle.
Run a second strategy? A third? A tenth? The idea is obvious. The implementation is not. A strategy portfolio creates problems that don't exist with a single bot:
Cascade strategy is an architectural pattern that solves these problems: the primary strategy gets the full position size, while the fallback strategy fills idle time with a reduced position.
Primary is a strategy with strict entry criteria. For example, triple timeframe with three confirming levels: signal on daily + 4-hour + hourly, with volatility and volume filtering.
Characteristics:
Fallback is a strategy with relaxed criteria. Dual timeframe, fewer filters, wider tolerances. It trades more frequently, but with lower edge per trade.
Characteristics:
timeline: ──────────────────────────────────────────────────
primary: ___████___________________████████____███________
fallback: ███____███████████████████________████___████████
capital: [dual][ full ][ dual_size ][ full ][ dual ]
When primary opens a position — fallback goes silent (or closes). When primary is idle — fallback trades at a reduced position (dual_size). Priority is unconditional: primary always displaces fallback.
Throughout the series we used three strategies. Here are their parameters for the 750-day period:
| Parameter | Strategy A | Strategy B | Strategy C |
|---|---|---|---|
| PnL | +55% | +27% | +300% |
| Trades | ~500 | ~40 | ~400 |
| Trading time | ~15% | ~5% | ~45% |
| MaxDD | ~0.9% | ~0.75% | ~17% |
| PnL/active day | 0.49%/d | 0.72%/d | 0.89%/d |
| Character | Medium activity | Rare, high conviction | Frequent, aggressive |
As we showed in PnL per Active Time, ranking by raw PnL and by PnL/active day produces different results. For cascade orchestration, the second metric is what matters.
dual_size is the fraction of the full position that the fallback strategy receives. It is the key cascade parameter:
Too large (e.g., 0.5 = 50%): when primary and fallback are active simultaneously, total exposure = 150% of target. Drawdown doubles. Loss-profit asymmetry makes this disproportionately expensive.
Too small (e.g., 0.01 = 1%): fallback fills 85% of idle time but earns pennies. Capital effectively sits idle.
Optimal: fallback contributes meaningful PnL without critically increasing drawdown during simultaneous operation with primary.
Let:
Total cascade PnL:
Total MaxDD (worst case — full correlation):
If we constrain total drawdown to :
In practice, the optimal dual_size is found via grid search on the cascade backtest:
import numpy as np
from dataclasses import dataclass
@dataclass
class CascadeResult:
dual_size: float
total_pnl: float
max_dd: float
sharpe: float
pnl_per_active_day: float
def grid_search_dual_size(
primary_equity: np.ndarray, # equity curve primary (minute bars)
fallback_equity: np.ndarray, # equity curve fallback (minute bars)
primary_positions: np.ndarray, # 1 = in position, 0 = flat
fallback_positions: np.ndarray,
grid: np.ndarray = np.arange(0.01, 0.30, 0.005),
) -> list[CascadeResult]:
"""
Grid search for dual_size.
primary_equity and fallback_equity are log-returns, minute bars.
"""
results = []
for d in grid:
fallback_active = fallback_positions & ~primary_positions
cascade_returns = (
primary_equity * primary_positions
+ d * fallback_equity * fallback_active
)
equity_curve = np.cumprod(1 + cascade_returns)
peak = np.maximum.accumulate(equity_curve)
drawdown = (equity_curve - peak) / peak
max_dd = drawdown.min()
total_pnl = equity_curve[-1] - 1
sharpe = (
np.mean(cascade_returns) / np.std(cascade_returns)
* np.sqrt(525_600) # minutes per year
) if np.std(cascade_returns) > 0 else 0
active_minutes = np.sum(primary_positions | fallback_active)
active_days = active_minutes / (24 * 60)
pnl_per_day = total_pnl / active_days if active_days > 0 else 0
results.append(CascadeResult(
dual_size=d,
total_pnl=total_pnl,
max_dd=max_dd,
sharpe=sharpe,
pnl_per_active_day=pnl_per_day,
))
return sorted(results, key=lambda r: r.sharpe, reverse=True)
Typical optimum for crypto strategies: dual_size in the range 0.05-0.10 (5-10% of full position). With Strategy B as primary (MaxDD 0.75%) and Strategy A as fallback (MaxDD 0.9%):
The drawdown constraint is not binding — the optimum is determined by cascade Sharpe. In practice, grid search typically yields (6.8%).
When there are more than two strategies, cascade generalizes to score-based allocation.
As described in detail in PnL per Active Time, the strategy score is calculated accounting for:
Strategy B with 40 trades requires a serious penalty. We use the lower bound of the confidence interval:
import scipy.stats as st
import numpy as np
def confidence_factor(trade_returns: np.ndarray, confidence: float = 0.95) -> float:
"""Confidence factor: 0..1, penalty for small samples."""
n = len(trade_returns)
if n < 10:
return 0.0
mean_r = np.mean(trade_returns)
if mean_r <= 0:
return 0.0
se = np.std(trade_returns, ddof=1) / np.sqrt(n)
t_crit = st.t.ppf(1 - (1 - confidence) / 2, df=n - 1)
ci_lower = mean_r - t_crit * se
return max(0.0, ci_lower / mean_r)
cf_b = confidence_factor(np.random.normal(0.0067, 0.028, 40))
cf_a = confidence_factor(np.random.normal(0.0011, 0.008, 500))
On perpetual futures, funding is paid every 8 hours. With leverage and average rate :
For Strategy A with MaxLev = 55x and average funding rate 0.01%:
With PnL/active day = 0.49%, net PnL is negative: /day. The strategy is unprofitable at full leverage. Detailed analysis in Funding Rates Kill Your Leverage.
The orchestrator manages strategies on trading pairs. Total number of potential positions: . But capital is limited — no more than simultaneous positions (slots) are allowed.
┌─────────────────────────────────────────────┐
│ ORCHESTRATOR │
│ │
│ Signal Queue (sorted by score): │
│ ┌──────────────────────────────────────┐ │
│ │ 1. Strategy C × ETHUSDT score=223 │ │
│ │ 2. Strategy B × BTCUSDT score=142 │ │
│ │ 3. Strategy A × SOLUSDT score=100 │ │
│ │ 4. Strategy C × BTCUSDT score=89 │ │
│ │ 5. Strategy A × ETHUSDT score=76 │ │
│ └──────────────────────────────────────┘ │
│ │
│ Active Slots (max_parallel = 3): │
│ ┌──────────────────────────────────────┐ │
│ │ Slot 1: Strategy C × ETHUSDT [FULL] │ │
│ │ Slot 2: Strategy B × BTCUSDT [FULL] │ │
│ │ Slot 3: Strategy A × SOLUSDT [DUAL] │ │
│ └──────────────────────────────────────┘ │
│ │
│ Conflict Rules: │
│ - One position per pair │
│ - Primary displaces fallback on same pair │
│ - Higher score wins for cross-pair slots │
└─────────────────────────────────────────────┘
from dataclasses import dataclass, field
from enum import Enum
from typing import Optional
import heapq
import time
class SlotType(Enum):
FULL = "full" # primary strategy, 100% position
DUAL = "dual" # fallback strategy, dual_size position
@dataclass
class Signal:
strategy_id: str
pair: str
direction: str # "long" | "short"
score: float
is_primary: bool # primary or fallback
timestamp: float
@dataclass(order=True)
class Slot:
"""A single orchestrator slot."""
priority: float = field(compare=True) # negative score for min-heap
strategy_id: str = field(compare=False)
pair: str = field(compare=False)
slot_type: SlotType = field(compare=False)
entry_time: float = field(compare=False)
class Orchestrator:
"""
Multi-strategy orchestrator with cascade mode.
Manages N strategies x M pairs within max_parallel_positions slots.
Primary strategies have unconditional priority over fallback.
"""
def __init__(
self,
max_parallel_positions: int = 10,
dual_size: float = 0.068,
min_score: float = 0,
):
self.max_parallel = max_parallel_positions
self.dual_size = dual_size
self.min_score = min_score
self.active_slots: dict[str, Slot] = {} # pair -> Slot
self.pending_signals: list[Signal] = []
def on_signal(self, signal: Signal) -> Optional[dict]:
"""
Process a new signal. Returns an action or None.
Actions:
- {"action": "open", "pair": ..., "size": ..., "slot_type": ...}
- {"action": "replace", "pair": ..., "close_strategy": ..., "open_strategy": ...}
- None (signal rejected)
"""
if signal.score < self.min_score:
return None
pair = signal.pair
if pair in self.active_slots:
existing = self.active_slots[pair]
if signal.is_primary and existing.slot_type == SlotType.DUAL:
self.active_slots[pair] = Slot(
priority=-signal.score,
strategy_id=signal.strategy_id,
pair=pair,
slot_type=SlotType.FULL,
entry_time=signal.timestamp,
)
return {
"action": "replace",
"pair": pair,
"close_strategy": existing.strategy_id,
"open_strategy": signal.strategy_id,
"size": 1.0,
}
if signal.score > -existing.priority:
slot_type = SlotType.FULL if signal.is_primary else SlotType.DUAL
size = 1.0 if signal.is_primary else self.dual_size
self.active_slots[pair] = Slot(
priority=-signal.score,
strategy_id=signal.strategy_id,
pair=pair,
slot_type=slot_type,
entry_time=signal.timestamp,
)
return {
"action": "replace",
"pair": pair,
"close_strategy": existing.strategy_id,
"open_strategy": signal.strategy_id,
"size": size,
}
return None # existing has higher priority
if len(self.active_slots) < self.max_parallel:
slot_type = SlotType.FULL if signal.is_primary else SlotType.DUAL
size = 1.0 if signal.is_primary else self.dual_size
self.active_slots[pair] = Slot(
priority=-signal.score,
strategy_id=signal.strategy_id,
pair=pair,
slot_type=slot_type,
entry_time=signal.timestamp,
)
return {
"action": "open",
"pair": pair,
"strategy": signal.strategy_id,
"size": size,
"slot_type": slot_type,
}
worst_pair = min(
self.active_slots,
key=lambda p: -self.active_slots[p].priority,
)
worst_slot = self.active_slots[worst_pair]
if signal.score > -worst_slot.priority:
del self.active_slots[worst_pair]
slot_type = SlotType.FULL if signal.is_primary else SlotType.DUAL
size = 1.0 if signal.is_primary else self.dual_size
self.active_slots[pair] = Slot(
priority=-signal.score,
strategy_id=signal.strategy_id,
pair=pair,
slot_type=slot_type,
entry_time=signal.timestamp,
)
return {
"action": "replace",
"pair": pair,
"close_strategy": worst_slot.strategy_id,
"close_pair": worst_pair,
"open_strategy": signal.strategy_id,
"size": size,
}
return None # all active slots have higher scores
def on_exit(self, pair: str) -> None:
"""Strategy closed a position."""
if pair in self.active_slots:
del self.active_slots[pair]
def utilization(self) -> float:
"""Current slot utilization."""
return len(self.active_slots) / self.max_parallel
def fill_efficiency_snapshot(self) -> float:
"""Weighted utilization: FULL=1.0, DUAL=dual_size."""
total = sum(
1.0 if s.slot_type == SlotType.FULL else self.dual_size
for s in self.active_slots.values()
)
return total / self.max_parallel
Three levels of conflict:
Level 1 — Same pair, same direction. The strategy with the higher score wins. If both are primary — score determines the winner. If one is primary and the other fallback — primary wins unconditionally.
Level 2 — Same pair, opposite direction. Prohibited: you cannot simultaneously be long and short on the same pair. The strategy with the highest score wins.
Level 3 — Cross-pair competition. When all slots are occupied, a new signal evicts the slot with the lowest score. This works as a priority queue.
The naive approach: backtest each strategy separately, sum the PnL. This produces an inflated result for three reasons:
Time overlap. When primary and fallback are active simultaneously, fallback should not trade (or trades at dual_size). Simple summing ignores this overlap.
Capital constraint. Total position is limited. If 5 strategies want to open simultaneously but there are only 3 slots — two strategies won't enter. Their PnL cannot be counted.
Transaction costs. Cascade switching (closing fallback, opening primary) generates additional commissions not present in individual backtests.
The correct cascade backtest is a joint simulation of all strategies on a shared timeline:
import numpy as np
from typing import NamedTuple
class Trade(NamedTuple):
strategy: str
pair: str
entry_time: int # minute index
exit_time: int # minute index
pnl_per_minute: float # log-return per minute
is_primary: bool
score: float
def backtest_cascade(
all_trades: list[Trade],
total_minutes: int,
max_slots: int = 10,
dual_size: float = 0.068,
switch_cost: float = 0.0006, # 0.06% round-trip
) -> dict:
"""
Joint simulation of cascade portfolio.
Walk through each minute, apply orchestrator rules,
calculate PnL accounting for overlap and slot constraints.
"""
entries = {}
exits = {}
active_trades = {} # trade_id -> Trade
for i, trade in enumerate(all_trades):
entries.setdefault(trade.entry_time, []).append((i, trade))
exits.setdefault(trade.exit_time, []).append((i, trade))
active_slots = {} # pair -> (trade_id, SlotType)
equity = np.ones(total_minutes)
switch_costs_total = 0.0
for t in range(1, total_minutes):
for trade_id, trade in exits.get(t, []):
if trade.pair in active_slots:
slot_id, _ = active_slots[trade.pair]
if slot_id == trade_id:
del active_slots[trade.pair]
new_signals = sorted(
entries.get(t, []),
key=lambda x: x[1].score,
reverse=True,
)
for trade_id, trade in new_signals:
pair = trade.pair
if pair in active_slots:
existing_id, existing_type = active_slots[pair]
existing_trade = all_trades[existing_id]
if trade.is_primary and existing_type == SlotType.DUAL:
active_slots[pair] = (trade_id, SlotType.FULL)
switch_costs_total += switch_cost
continue
if trade.score > existing_trade.score:
slot_type = SlotType.FULL if trade.is_primary else SlotType.DUAL
active_slots[pair] = (trade_id, slot_type)
switch_costs_total += switch_cost
elif len(active_slots) < max_slots:
slot_type = SlotType.FULL if trade.is_primary else SlotType.DUAL
active_slots[pair] = (trade_id, slot_type)
minute_return = 0.0
for pair, (trade_id, slot_type) in active_slots.items():
trade = all_trades[trade_id]
size = 1.0 if slot_type == SlotType.FULL else dual_size
minute_return += trade.pnl_per_minute * size
equity[t] = equity[t - 1] * (1 + minute_return)
peak = np.maximum.accumulate(equity)
max_dd = ((equity - peak) / peak).min()
total_pnl = equity[-1] - 1 - switch_costs_total
return {
"total_pnl": total_pnl,
"max_dd": max_dd,
"switch_costs": switch_costs_total,
"equity_curve": equity,
}
Each cascade switch (fallback -> primary) requires:
Total switch cost: ~0.06-0.10% per switch. With 100 switches over the period:
This is a significant amount. A cascade with frequent switching can underperform a single strategy due to transaction costs.
3 strategies on 10 pairs = 30 potential signals. With max_slots = 5, the orchestrator selects the top 5 by score. This is a combinatorial problem: possible portfolios at each moment.
In practice, a greedy algorithm (sort by score, fill top-down) produces near-optimal results in .
Crypto pairs are strongly correlated. BTC drops — ETH, SOL, AVAX drop together. This means 5 long positions on 5 different pairs are effectively one large position on the "crypto market."
As we analyzed in detail in Signal Correlation, the effective number of independent positions:
where is the average correlation between pairs.
With and :
Five positions on correlated pairs are equivalent to 1.3 independent positions. Diversification is virtually absent.
def effective_diversification(
positions: list[dict], # [{"pair": "BTCUSDT", "direction": "long"}, ...]
correlation_matrix: np.ndarray,
pair_index: dict[str, int],
) -> float:
"""
Calculate effective diversification of open positions.
Returns:
N_eff / N — diversification coefficient (0..1)
"""
n = len(positions)
if n <= 1:
return 1.0
total_corr = 0.0
pairs_count = 0
for i in range(n):
for j in range(i + 1, n):
idx_i = pair_index[positions[i]["pair"]]
idx_j = pair_index[positions[j]["pair"]]
rho = correlation_matrix[idx_i, idx_j]
if positions[i]["direction"] != positions[j]["direction"]:
rho = -rho
total_corr += rho
pairs_count += 1
avg_rho = total_corr / pairs_count if pairs_count > 0 else 0
n_eff = n / (1 + (n - 1) * max(0, avg_rho))
return n_eff / n
The orchestrator should account for correlation when filling slots. Two options:
The full pipeline from data to production consists of 8 stages:
Load historical data, build Parquet cache for multi-timeframe access. Without efficient caching, subsequent stages are unacceptably slow.
Select the base timeframe and indicator window lengths. Coarse grid: TF from {1m, 5m, 15m, 1h, 4h}, Length from {10, 20, 50, 100, 200}. Hill-climbing from the best grid point.
Optimize separation parameters (entries/exits). Coordinate descent over 12 parameters — indicator thresholds, filters, stop-losses, take-profits. Coordinate descent is cheaper than Optuna for high-dimensional deterministic objective functions.
Meta-parameters: max hold time, min PnL for exit, trailing stop configuration. Again coordinate descent. Check robustness via plateau analysis — if the optimum is point-like, the strategy is over-optimized.
Grid search over pairs (Primary, Fallback). For each combination: select dual_size, calculate cascade PnL via joint simulation.
Multi-level validation:
Rank cascade combinations by score. Top-K combinations advance to Stage 7. Score accounts for confidence adjustment, funding costs, and fill_efficiency.
Final stage: launch the orchestrator on strategies and pairs in cascade mode. Slot management, priority queue, conflict resolution — everything described above.
Suppose primary trades of the time with PnL/day = 0.49%. Fallback trades with PnL/day = 0.89%. Overlap = (assuming independence).
Primary alone (Strategy A):
Cascade (A primary + C fallback):
Cascade gain: +31% to PnL from fallback, with minimal drawdown increase ( added to MaxDD).
Cascade is ineffective when:
| Configuration | Annual PnL | MaxDD | Sharpe | Switch costs |
|---|---|---|---|---|
| Strategy A alone | 26.8% | 0.9% | 1.42 | 0 |
| Strategy C alone | 146.1% | 17% | 1.15 | 0 |
| Cascade A+C (d=0.068) | 35.2% | 2.06% | 1.58 | ~1.2% |
| Cascade B+A (d=0.068) | 19.4% | 1.36% | 1.71 | ~0.3% |
| 3-strategy orchestrator | 48.7% | 3.1% | 1.63 | ~2.1% |
Cascade A+C: primary A gains +8.4% from fallback C. Sharpe rises through idle time utilization. MaxDD grows moderately ().
The fill_efficiency parameter determines what fraction of idle time the orchestrator actually utilizes. As shown in PnL per Active Time, it can be estimated three ways:
For a cascade with 3 strategies on 10 pairs:
def cascade_fill_efficiency(
strategies: list[dict], # [{"trading_time": 0.15, "is_primary": True}, ...]
n_pairs: int = 10,
correlation_factor: float = 3.0,
) -> float:
"""Estimate fill_efficiency for a cascade portfolio."""
n_eff = n_pairs / correlation_factor
primary_times = [s["trading_time"] for s in strategies if s["is_primary"]]
p_primary = 1 - np.prod([(1 - t) ** n_eff for t in primary_times])
fallback_times = [s["trading_time"] for s in strategies if not s["is_primary"]]
p_fallback = 1 - np.prod([(1 - t) ** n_eff for t in fallback_times])
fill = p_primary + (1 - p_primary) * p_fallback
return min(fill, 1.0)
strategies = [
{"trading_time": 0.05, "is_primary": True}, # Strategy B
{"trading_time": 0.15, "is_primary": True}, # Strategy A
{"trading_time": 0.45, "is_primary": False}, # Strategy C as fallback
]
eff = cascade_fill_efficiency(strategies, n_pairs=10, correlation_factor=3.0)
Don't launch 10 strategies on 20 pairs right away. Start with one primary + one fallback on 3-5 pairs. Make sure the joint simulation matches real behavior. Backtest-live parity is critical: if the cascade backtest diverges from live by even 5-10% — there's an error in orchestrator logic.
The optimal dual_size depends on the specific pair of strategies. 6.8% is a guideline, not a universal constant. Run grid search from 1% to 30% with 0.5% steps and select the Sharpe maximum.
With max_slots = 1, cascade degenerates into simple strategy switching. With max_slots = 50, the constraint is not binding and the problem reduces to an independent portfolio. The interesting zone: max_slots = 3-10, where slot management genuinely impacts results.
In live trading, cascade switching is not instantaneous. Closing a fallback position + opening primary = 2 API calls + network latency + exchange matching. On a volatile market, the price can move in 200-500ms. Build in a slippage budget.
Track real fill_efficiency in production. If it is significantly lower than backtested — the orchestrator is not utilizing idle time as expected. Causes: API delays, rejected orders, margin constraints.
Cascade parameters (dual_size, score weights, slot limits) should not be static. Use adaptive drill-down for periodic recalibration on fresh data. The market changes — cascade parameters should follow.
This article is the finale of a 13+ article series. Each article addressed one specific problem on the path from backtest to production. Here's how they connect:
Loss-Profit Asymmetry — the multiplicative nature of returns, volatility drag, Kelly criterion. This is the mathematical foundation for everything that follows: why MaxDD determines leverage, why Sharpe matters more than raw PnL, why a 50% win rate with symmetric R:R is unprofitable.
Monte Carlo Bootstrap — turning a single-point estimate into a distribution with confidence intervals. Any metric (PnL, MaxDD, Sharpe) only makes sense with a confidence interval.
Walk-Forward Optimization — out-of-sample validation. A backtest on historical data is an IS result; WFO shows how the strategy performs on new data.
Plateau Analysis — parameter robustness check. If the optimum is point-like, the strategy is over-optimized.
Backtest-Live Parity — comparing backtest with real results. The final check before scaling.
Funding Rates Kill Leverage — the hidden cost of leverage on perpetual futures. Without accounting for funding, a beautiful backtest turns into a loss.
Funding Rate Arbitrage — how to turn funding from an expense into a revenue source through cross-exchange strategies.
PnL per Active Time — the metric for ranking strategies in a portfolio. Raw PnL doesn't scale; PnL/active day does.
Signal Correlation — effective diversification in a portfolio of correlated pairs.
Parquet Cache for Multi-Timeframe Backtests — data infrastructure for fast iterations.
Adaptive Drill-Down — adaptive optimization: coarse grid -> fine-tuning in promising zones.
Optuna vs. Coordinate Descent — optimizer selection: Optuna for low dimensions with noisy objectives, coordinate descent for high dimensions with smooth objectives.
Polars vs Pandas — DataFrame operation performance for backtesting.
Cascade Strategies — combining all previous components into a working system. Score-based allocation uses PnL/active time, confidence adjustment, funding costs. Cascade mode fills idle time. Joint simulation validates the portfolio. Monte Carlo bootstrap provides confidence intervals for cascade PnL.
Each article is an independent module. Together they form a complete pipeline from data loading to live orchestration of a strategy portfolio.
Cascade is not the only approach to strategy portfolios. But it is one of the simplest and most practical: the primary strategy trades at full capacity, fallback fills idle time at a reduced position. Two key parameters (dual_size and max_slots) provide sufficient flexibility for most configurations.
Three takeaways:
Cascade must be backtested via joint simulation only. Summing individual PnL inflates results. Switch costs, overlap, slot constraints — all of this is only captured in joint simulation.
dual_size determines the PnL vs. drawdown trade-off. Typical optimum is 5-10%. Grid search on Sharpe is a reliable selection method.
The orchestrator is a score-based priority queue. Everything reduces to a single number (score) for each signal. Score = f(PnL/active day, MaxLev, confidence, funding). Strategies with the highest score get slots. The rest wait.
The "Backtests Without Illusions" series demonstrates one thing: between a beautiful backtest and real profit lie dozens of pitfalls. Each article removes one. Cascade orchestration is the last step: turning a set of validated strategies into a working portfolio.
@article{soloviov2026cascadestrategies, author = {Soloviov, Eugen}, title = {Cascade Strategies: Priority Execution with Fallback Filling}, year = {2026}, url = {https://marketmaker.cc/ru/blog/post/cascade-strategies-orchestration}, version = {0.1.0}, description = {Finale of the "Backtests Without Illusions" series. How to build an orchestrator from N strategies x M pairs, implement cascade mode with priority and fallback filling, choose dual\_size, and why strategy portfolios cannot be backtested by summing PnL.} }