wslc: expose container lifecycle events in Microsoft.WSL.Containers

Is your feature request related to a problem? Please describe.

WSLC already has a Docker-style container event stream through the underlying COM API added in #40971:

• IWSLCSession::GetEvents
• IWSLCEventStream::GetNext

The same functionality is also available from the CLI through wslc events.

However, it doesn't appear to be exposed through the public Microsoft.WSL.Containers C#/WinRT API.

As of the 2.9.12 prerelease, the public Session API exposes events such as Terminated and ProcessCrashed, but there is no supported way to subscribe to container lifecycle events such as:

• create
• start
• kill
• stop
• destroy

For an application using the SDK directly, this means container state has to be refreshed by polling even though WSLC already has the underlying event stream.

My use case is a desktop container manager. Ideally it would take an initial snapshot of the containers, apply lifecycle events as incremental updates, and occasionally reconcile the full state in case an event was missed or the stream had to reconnect.

Without an events API in the public SDK, the alternatives are polling or launching wslc events as a separate process.

Describe the solution you'd like

Expose the existing container event stream through Microsoft.WSL.Containers.

It doesn't necessarily need to mirror the COM API exactly, but it would be useful to expose the same basic capabilities:

• container lifecycle events;
• since / until ranges;
• event filters;
• an asynchronous way to consume events;
• cancellation / disposal;
• a way to detect lost events and the end of the stream.

For example, conceptually:

var stream = session.GetEvents(options);

while (true)
{
    var containerEvent = await stream.GetNextAsync();
    // Update the affected container.
}

An event-based API or an async-stream-style API would work as well. I'm mainly looking for a supported public API for the event stream that already exists underneath the SDK.

It would also be useful if the public API preserved equivalents of the existing WSLC_E_EVENTS_LOST and WSLC_E_EVENT_STREAM_FINISHED conditions so callers can reconcile state or stop reading as appropriate.

Describe alternatives you've considered

Polling container state

Periodically refresh the container list or inspect individual containers.

This works, but adds unnecessary polling and makes UI updates less immediate.

Invoking wslc events

Launch the CLI and parse its output.

This provides the information, but adds an extra process and parsing/lifetime management for functionality that already exists in WSLC.

Using the underlying COM API directly

IWSLCSession::GetEvents already exposes the functionality, but relying on the underlying COM interface directly doesn't seem like a good long-term dependency for a third-party application.

Additional context

The underlying event-stream implementation was added in #40971, so this request is mainly about making that capability available through the supported Microsoft.WSL.Containers API.

This would be useful for desktop container managers, IDE integrations, monitoring tools, and other SDK consumers that need to react to container state changes in real time.

I'd be happy to contribute an implementation once the preferred public API shape is agreed on.