Named job lifecycle discipline

A long-lived object — a service handler, a screen model, a session controller — launches background work from callbacks it does not control and that fire more often than anyone expects. Left unmanaged, each firing leaks another live coroutine doing the same thing.

The shape that survives is one nullable Job field per concern, never one shared field for several:

// adapted — a representative slice; the real list is longer
private var progressJob: Job? = null
private var bufferedJob: Job? = null
private var sleepTimerJob: Job? = null
private var loadJob: Job? = null
private var metadataJob: Job? = null
// …one per concern