// only accepts PodUpdates
func (c *PodConfig) Channel(ctx context.Context, source string) chan<- interface{} {
	c.sourcesLock.Lock()
	defer c.sourcesLock.Unlock()
	c.sources.Insert(source)
	return c.mux.ChannelWithContext(ctx, source)
}

// SeenAllSources returns true if seenSources contains all sources in the
// config, and also this config has received a SET message from each source.