Class AsyncStoredChannelTransfer<T>

Output channel with value retention, external management, and async interface.

Capabilities: isOutput, isSubscribable, isAsyncPullable, isAsyncTriggerable

Mechanics:

1. setup(emit) / destroy() — sync, like in StoredChannelTransfer
2. emit(data) — sync, writes the value, calls asyncTrigger (fire-and-forget)
3. asyncPull() — returns the current value (trivially async)
4. asyncTrigger() — notifies subscribers (trivially async)
5. subscribe(handler) — sync subscription

Note: setup/emit/subscribe are synchronous (subscription remains sync), but pull/trigger are async for integration with async pipelines.

Configuration (AsyncStoredChannelTransferConfig):

• setup: (emit: DataHandler) => void
• destroy: () => void
• initialValue?: T
• onError?, onDestroyError?: ErrorHandler