How to override Vendure's promotion system to allow only one promotion per order?

[DuongVanDuc97]

Vendure's built-in promotion system allows multiple promotions to be applied to a single order simultaneously, and non-coupon promotions are automatically evaluated and applied when orders are modified. However, my business requirements dictate that only one promotion can be applied to an order at a time (similar to how many retail stores operate).

Desired Behavior

• Only one promotion (either auto or coupon-based) should be active per order
• When a new promotion becomes applicable, it should either:
  • Replace the existing promotion if it's more beneficial, OR
  • Be rejected if a promotion is already applied
• Users should have control over which promotion to keep when conflicts arise

I've considered several approaches, but they all seem to require aggressive modifications to Vendure's core methods

Has anyone implemented similar functionality? What approach would you recommend for overriding Vendure's default promotion behavior?