The risk model

risk.json in the project, or Arvo's defaults when there is none. One model, in the backtest and in every session. A field not set is not set, and the Risk tab says so rather than showing a default as if you chose it.

Field	What
stop_atr_multiple	Stop distance as a multiple of ATR. Not set runs with no stop
atr_period	Bars the ATR is averaged over
risk_per_trade	Fraction of starting capital a stop-out may cost. Needs a stop
max_position_fraction	Fraction of starting capital one position may occupy. Above 1 is leverage
max_drawdown	Fall from the account's peak that stops the rule for the run. Permanent
max_concurrent_positions	The most positions held at once across a book
max_daily_loss	Realised loss in one day, as a fraction of starting capital, that refuses new entries
correlation_cap	Above this pairwise correlation, names are one bet; how many such bets may be held. Refuses when unknown
sector_cap	The most positions one sector may hold, with each name's sector. Refuses an unlabelled name
day_trading	unconstrained, or pattern_day_trader: three round trips per five days under $25k

Costs — slippage, commission, a per-fill fee, an option spread — are on the experiment, recorded with every finding, and the paper session's measured slippage is reported against what the backtest assumed.