Fix buy/lay commission handling for upfront vig

[nova-rey]

Summary

• add an explicit buy_vig_on_win table setting and expose bet placement_cost helpers
• track wager and vig bookkeeping on Buy and Lay bets so upfront commission reduces bankroll immediately and losses include the fee
• update Player.add_bet to respect placement costs and add focused unit tests covering the vig-on-placement scenarios

Testing

• pytest tests/unit/test_buy_lay_commission.py
• pytest tests/unit/test_bet.py

---

https://chatgpt.com/codex/tasks/task_e_6908b663c9508328991e2235630c54fa

[chatgpt-codex-connector]

💡 Codex Review

crapssim/crapssim/bet.py

Lines 858 to 862 in 5ee54ca

	if table.settings.get("buy_vig_on_win", True):
	return self.wager
	commission = _compute_commission(
	table, gross_win=self.wager, bet_amount=self.wager
	)

Charge lay upfront commission on the wrong base

When vig is collected upfront (buy_vig_on_win=False), Lay.placement_cost computes the commission using self.wager, which is the amount risked, rather than the potential win self.payout_ratio * self.wager that _compute_commission expects and that is used when vig is taken on the win. As a result, a lay 4 for $40 is charged commission on $40 instead of the $20 it can win, so players are debited $2 instead of $1 and losses also overstate vig. Every lay bet with upfront vig will overcharge the bankroll by the payout ratio.

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