flutter-in-app-purchaseslisted

# Flutter In-App Purchases Model store billing as an asynchronous reconciliation system, not a button callback. Preserve the project's current store package, subscription service, backend, account model, and state management unless migration is explicitly requested. Installing this skill requires no store account, API credential, signing material, or product configuration. Do not create products, change pricing, upload builds, or mutate live store configuration without explicit authorization. ## Preflight Read `pubspec.yaml`, SDK constraints, supported platforms, store package and native configuration, product identifiers, purchase listener ownership, entitlement source of truth, backend verification, authentication, persistence, tests, flavors, and sandbox setup. Distinguish consumables, non-consumables, and subscriptions before editing the flow. Keep three concepts separate: - Store catalog: products, localized price, availability, offers, and store metadata. - Transaction: pending, purchased, restored, cancelled, failed, consumed, acknowledged, or finished as supported by the store. - Entitlement: the product capability the application currently grants to an account or device. Never grant an entitlement from a button tap, client assertion, unverified payload, or pending transaction. Process verified completed transactions idempotently, then perform the store-required acknowledgement, consumption, or finish step exactly as the product type requires. ## Load referenc