Core Concepts

GlowBack is an event‑driven backtesting system. Understanding a few core concepts helps you reason about results and performance.

Key Ideas

• Events: Market data is processed in chronological order across symbols.
• Strategies: Logic that emits orders in response to events.
• Execution: Orders fill with realistic slippage, latency, and commission.
• Portfolio: Tracks positions, cash, and P&L over time.
• Results: Metrics and artifacts (equity curve, trades) for evaluation.

Supported account modes

Mode	Current behavior	Constraints / notes
Backtest portfolio (gb-types::Portfolio)	Supports long and short positions, multi-symbol books, fractional quantities, commissions, realized P&L, unrealized P&L, and marked-to-market equity snapshots.	Equity is computed from cash plus signed position market value. Short exposure is modeled as a liability. Margin interest and broker-specific borrowing rules are not modeled yet.
Sandbox paper broker (gb-live::PaperBroker)	Cash account for live-like dry runs with fills, positions, and account balance snapshots.	Rejects buys that exceed available cash and rejects sell orders that exceed held inventory. No naked shorts or margin borrowing.

The regression suite now treats these accounting rules as explicit invariants so trade-to-trade portfolio snapshots stay auditable instead of being inferred from aggregate returns alone.