Controller doesn't stop processing as soon as client disconnects

The controller that orchestrates the screen host and screen provider does not immediately stop processing when the screen host transport is no longer available for use. We need to create some sort of API that allows the transport to notify when the connection is finished.

Look at the controller code that manages the screen host and provider. Identify the transport layer and how it currently detects availability. The task is to design an API for the transport to signal disconnection, likely involving event channels or callbacks. Check existing tests for the transport to understand the current interface.

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