Generation
The epoch a piece of state belongs to, within the timeline that produced it.
Packets, frames, queues and decoders carry a pipeline epoch. Seeking or rebuilding retires that epoch, so stale work can be discarded. An in-place audio selection keeps the video epoch valid; AudioTap and AudioClockSnapshot therefore share a separate audio generation that also changes at that selection. Compare generations only within the same producer and timeline.
The identifier complements the worker quiesce and flush handshake; it does not make mutable pipeline state safe to change while a worker still owns it.
Generation 0 is the initial one and is valid. "Not started" is expressed as a null Generation?, never as a reserved value.