.NET: runtime logs forwarding session.idle, but SDK callback never delivers it

No specific files are named. Start by tracing the .NET session subscription and FIFO dispatch path, then inspect the proposed session.waitForIdle runtime contract alongside session.idle and GetEventsAsync handling. Done means a regression test shows completion waits for all preceding events, handles dropped idle notifications, surfaces failures, and supports cancellation.

Summary

Visual Studio can remain indefinitely in the running state after the Copilot CLI has completed a response.

The CLI verbose log shows that it forwarded the terminal, ephemeral session.idle event. The .NET SDK subscription receives the preceding events, including the final assistant.turn_end, but never receives SessionIdleEvent.

Because session.idle is ephemeral, it cannot be recovered later through GetEventsAsync(). The client therefore has no authoritative completion signal and continues waiting.

Environment

• GitHub.Copilot.SDK: 1.0.1
• Copilot CLI runtime: 1.0.61
• Windows ARM64
• Visual Studio Agent and Agent (Preview) modes

The current SDK 1.0.7 still does not expose a durable idle wait or event-dispatch flush API.

Observed behavior

The CLI log ends with:

Forwarding event ... assistant.turn_end
Forwarding event ... session.idle (ephemeral)

The .NET subscriber observes assistant.turn_end, but not session.idle. The operation remains active even though the runtime has finished.

The absence of session.idle from events.jsonl is expected because the event is ephemeral; it does not explain why the live subscriber missed it.

Why assistant.turn_end is insufficient

In multi-turn tool workflows, an intermediate assistant.turn_end can be followed immediately by another assistant.turn_start. Completion also needs to account for sub-agents, attached shells, queued messages, and follow-up notification turns.

Requested fix

Please provide an authoritative completion contract owned by the runtime/SDK, for example:

await session.WaitForIdleAsync(cancellationToken);

It should:

1. Wait for turns, sub-agents, attached shells, queued work, and follow-up turns to settle.
2. Resolve only when the runtime is fully idle.
3. Ensure preceding session events have crossed the .NET SDK FIFO dispatch queue.
4. Surface session errors and transport failures.
5. Remain correct if the live session.idle notification is dropped.
6. Support cancellation without leaving an orphaned waiter.

An equivalent session.waitForIdle runtime RPC combined with an SDK dispatch barrier would also work.

Regression test

Add a .NET test where a multi-turn response completes, the live session.idle notification is deliberately dropped, and the completion wait still resolves only after all preceding assistant and tool events have been delivered.

Related

• #794 - identifies missing session.idle and silent notification drops, but its proposed fallback did not ship
• #558 - timeout waiting for session.idle
• #791 - serialized FIFO event dispatch in the .NET SDK
• #927 - ephemeral events are intentionally unavailable through replay
• #1275 - assistant.turn_end alone is not a completion signal