How do Price Rules work in CPQ? Describe their architecture.

Price Rules (SBQQ__PriceRule__c) dynamically set field values on quote lines or the quote header based on conditions. Architecture:

1. Price Rule: The parent record defining when the rule fires — either on calculator (when the quote calculator runs) or on save. It has an evaluation scope (quote, quote line, or both) and an evaluation event (always, on add, or on calculate).
2. Price Conditions (SBQQ__PriceCondition__c): Child records of the Price Rule that define qualifying criteria. Each condition specifies a tested object (Quote, Quote Line, Summary Variable), a field, an operator, and a value. Multiple conditions can use AND/OR logic.
3. Price Actions (SBQQ__PriceAction__c): Child records that specify what happens when conditions are met — the target object (Quote or Quote Line), the target field, and the source (a formula, a field lookup, or a summary variable). Common use cases: set a special price on a quote line when a specific product combination is selected, populate a custom discount field based on a contract tier, or lock a price for a specific account segment.