Centralized event access validation into a reusable `validate_event_access` function, eliminating duplicated code across endpoints. Updated the logic in `get_event` and `get_event_by_slug` to use this function. Adjusted tests to align with the refactored logic and fixed permission-based response statuses.
Updated event API to enforce stricter access controls based on user roles, including creators, managers, superusers, and guests. Added robust test cases for creating, fetching, and handling event access scenarios to ensure consistent behavior across endpoints.
