Build a rule engine

• A rule has an id, a priority, a condition and one or more actions; engine.evaluate(facts) finds the rules whose condition holds for the facts object and executes their actions
• Conditions combine with AND, OR and NOT and nest to any depth; leaf conditions compare a fact path (for example order.total, user.address.country) with a value
• Operators: eq, neq, gt, gte, lt, lte, in, notIn, contains and matches (regular expression), with clear behaviour for missing facts and type mismatches
• Rules run in descending priority; the engine supports a mode that stops after the first matching rule and a mode that runs all matching rules, and actions may update the facts for later rules (with a limit that prevents infinite loops)
• Rules and actions are loaded from JSON, validated for structure, operators and known action names, with errors that identify the rule and the field; actions are registered by name in the engine
• evaluate returns which rules fired and their action results, and an explanation (trace) option lists why each rule matched or did not

Only after every requirement works.

• Rule versions and enable or disable flags
• Compile conditions to functions once for speed
• A small expression syntax such as order.total > 100 and user.tier == "gold"