Allow assistants to run in the background (#828)

app/MindWork AI Studio/Tools/AssistantSessions/AssistantSessionSnapshot.cs

@@ -0,0 +1,68 @@
+using AIStudio.Chat;
+
+namespace AIStudio.Tools.AssistantSessions;
+
+/// <summary>
+/// Immutable-style view of an assistant session for UI consumers and message bus events.
+/// </summary>
+/// <remarks>
+/// The service creates snapshots by copying its internal runtime state. Consumers must
+/// treat the contained chat thread and state objects as read-only views of the session.
+/// </remarks>
+public sealed record AssistantSessionSnapshot
+{
+    /// <summary>
+    /// Identifies the concrete run represented by this snapshot.
+    /// </summary>
+    public required Guid SessionId { get; init; }
+
+    /// <summary>
+    /// Identifies the assistant and logical session slot represented by this snapshot.
+    /// </summary>
+    public required AssistantSessionKey Key { get; init; }
+
+    /// <summary>
+    /// Gets the user-visible assistant title.
+    /// </summary>
+    public required string Title { get; init; }
+
+    /// <summary>
+    /// Gets the current lifecycle status.
+    /// </summary>
+    public required AssistantSessionStatus Status { get; init; }
+
+    /// <summary>
+    /// Gets when the session run started.
+    /// </summary>
+    public required DateTimeOffset StartedAt { get; init; }
+
+    /// <summary>
+    /// Gets when the session was last changed.
+    /// </summary>
+    public required DateTimeOffset UpdatedAt { get; init; }
+
+    /// <summary>
+    /// Gets when the session reached a terminal state.
+    /// </summary>
+    public DateTimeOffset? FinishedAt { get; init; }
+
+    /// <summary>
+    /// Gets the user-visible error message for failed sessions.
+    /// </summary>
+    public string ErrorMessage { get; init; } = string.Empty;
+
+    /// <summary>
+    /// Gets the assistant chat thread captured for this session.
+    /// </summary>
+    public ChatThread? ChatThread { get; init; }
+
+    /// <summary>
+    /// Gets the assistant component state captured for this session.
+    /// </summary>
+    public IReadOnlyDictionary<string, IAssistantSessionSnapshotField> State { get; init; } = new Dictionary<string, IAssistantSessionSnapshotField>();
+
+    /// <summary>
+    /// Gets whether the session is still running or canceling.
+    /// </summary>
+    public bool IsActive => this.Status is AssistantSessionStatus.RUNNING or AssistantSessionStatus.CANCELING;
+}