Task Dependency Scheduler

You are given a list of tasks where each task is represented as an object with the following properties:

• id: A unique identifier for the task (e.g., a string or number).
• prerequisites: An array of task ids that must be completed before this task can begin.
• priority: An integer indicating the task's priority (with a lower number indicating a higher priority).

Write a function in the programming language of your choice that takes this list of tasks and returns a valid ordering (schedule) of task ids such that:

1. For every task, all its prerequisite tasks appear before it in the ordering.
2. When multiple tasks are available to be scheduled (i.e., all prerequisites have been met), the task with the higher priority (the lower priority number) is selected first.

If it is not possible to generate a valid ordering due to a cycle in the prerequisites, your function should report this by either raising an error or returning an appropriate indicator of the failure.

Assume that the input is provided as an array (or list) of task objects. Ensure that your solution is efficient and well-documented.