Evaluates whether a customer can access a feature, with optional pre-flight usage simulation.

Without track: Returns an isAllowed decision with a reason — identical in outcome to the GET check, but usable when you need a POST interface.

With track: Simulates whether the proposed usageUnits would be permitted under the customer's current plan limits — without recording real consumption. Use this to pre-flight expensive operations before they happen: check if a customer has 10,000 tokens remaining before firing an LLM call, for example. A zero-usage audit event is always written for traceability.

Important: When track is provided without usageUnits, the simulation assumes 1 unit. This endpoint does not record billable usage — to meter actual consumption, use the Events endpoint (POST /api/v1/client/events).