@@ -122,7 +122,7 @@
     <File Path="samples/02-agents/Harness/README.md" />
     <Project Path="samples/02-agents/Harness/Harness_Shared_Console/Harness_Shared_Console.csproj" />
     <Project Path="samples/02-agents/Harness/Harness_Step01_Research/Harness_Step01_Research.csproj" />
-    <Project Path="samples/02-agents/Harness/Harness_Step02_Research_WithSubAgents/Harness_Step02_Research_WithSubAgents.csproj" />
+    <Project Path="samples/02-agents/Harness/Harness_Step02_Research_WithBackgroundAgents/Harness_Step02_Research_WithBackgroundAgents.csproj" />
     <Project Path="samples/02-agents/Harness/Harness_Step03_DataProcessing/Harness_Step03_DataProcessing.csproj" />
     <Project Path="samples/02-agents/Harness/ConsoleReactiveFramework/ConsoleReactiveFramework.csproj" />
     <Project Path="samples/02-agents/Harness/ConsoleReactiveComponents/ConsoleReactiveComponents.csproj" />

@@ -6,26 +6,26 @@
 namespace Harness.Shared.Console.ToolFormatters;
 
 /// <summary>
-/// Formats <c>SubAgents_*</c> tool calls with human-readable details
+/// Formats <c>BackgroundAgents_*</c> tool calls with human-readable details
 /// for task start, continue, wait, and result retrieval operations.
 /// </summary>
-public sealed class SubAgentToolFormatter : ToolCallFormatter
+public sealed class BackgroundAgentToolFormatter : ToolCallFormatter
 {
     /// <inheritdoc/>
-    public override bool CanFormat(FunctionCallContent call) => call.Name.StartsWith("SubAgents_", StringComparison.Ordinal);
+    public override bool CanFormat(FunctionCallContent call) => call.Name.StartsWith("BackgroundAgents_", StringComparison.Ordinal);
 
     /// <inheritdoc/>
     public override string? FormatDetail(FunctionCallContent call) => call.Name switch
     {
-        "SubAgents_StartTask" => FormatStartSubTask(call),
-        "SubAgents_WaitForFirstCompletion" => FormatIdList(call, "taskIds", "Wait for"),
-        "SubAgents_GetTaskResults" => FormatSingleId(call, "taskId"),
-        "SubAgents_ContinueTask" => FormatContinueTask(call),
-        "SubAgents_ClearCompletedTask" => FormatSingleId(call, "taskId"),
+        "BackgroundAgents_StartTask" => FormatStartBackgroundTask(call),
+        "BackgroundAgents_WaitForFirstCompletion" => FormatIdList(call, "taskIds", "Wait for"),
+        "BackgroundAgents_GetTaskResults" => FormatSingleId(call, "taskId"),
+        "BackgroundAgents_ContinueTask" => FormatContinueTask(call),
+        "BackgroundAgents_ClearCompletedTask" => FormatSingleId(call, "taskId"),
         _ => null,
     };
 
-    private static string? FormatStartSubTask(FunctionCallContent call)
+    private static string? FormatStartBackgroundTask(FunctionCallContent call)
     {
         string? agentName = GetStringArgumentValue(call, "agentName");
         string? description = GetStringArgumentValue(call, "description");

@@ -19,7 +19,7 @@ public sealed class TodoToolFormatter : ToolCallFormatter
     public override string? FormatDetail(FunctionCallContent call) => call.Name switch
     {
         "TodoList_Add" => FormatAddTodos(call),
-        "TodoList_Complete" => FormatIdList(call, "ids", "Complete"),
+        "TodoList_Complete" => FormatCompleteTodos(call),
         "TodoList_Remove" => FormatIdList(call, "ids", "Remove"),
         _ => null,
     };
@@ -64,6 +64,50 @@ public sealed class TodoToolFormatter : ToolCallFormatter
         return sb.ToString();
     }
 
+    private static string? FormatCompleteTodos(FunctionCallContent call)
+    {
+        if (call.Arguments?.TryGetValue("items", out object? itemsObj) != true || itemsObj is null)
+        {
+            return null;
+        }
+
+        var entries = new List<(int Id, string? Reason)>();
+
+        if (itemsObj is JsonElement jsonArray && jsonArray.ValueKind == JsonValueKind.Array)
+        {
+            foreach (JsonElement item in jsonArray.EnumerateArray())
+            {
+                if (!item.TryGetProperty("id", out JsonElement idElement) || !idElement.TryGetInt32(out int id))
+                {
+                    continue;
+                }
+
+                string? reason = item.TryGetProperty("reason", out JsonElement reasonElement)
+                    ? reasonElement.GetString()
+                    : null;
+                entries.Add((id, reason));
+            }
+        }
+
+        if (entries.Count == 0)
+        {
+            return null;
+        }
+
+        var sb = new StringBuilder();
+        for (int i = 0; i < entries.Count; i++)
+        {
+            string connector = i < entries.Count - 1 ? "├─" : "└─";
+            sb.Append($"\n   {connector} Complete #{entries[i].Id}");
+            if (!string.IsNullOrEmpty(entries[i].Reason))
+            {
+                sb.Append($" — {Truncate(entries[i].Reason!, 80)}");
+            }
+        }
+
+        return sb.ToString();
+    }
+
     private static string? FormatIdList(FunctionCallContent call, string paramName, string verb)
     {
         List<int>? ids = GetIntListArgumentValue(call, paramName);

@@ -56,7 +56,7 @@ public static List<ToolCallFormatter> BuildDefaultToolFormatters()
         [
             new TodoToolFormatter(),
             new ModeToolFormatter(),
-            new SubAgentToolFormatter(),
+            new BackgroundAgentToolFormatter(),
             new FileMemoryToolFormatter(),
             new WebSearchToolFormatter(),
             new FallbackToolFormatter(),

@@ -1,10 +1,10 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-// This sample demonstrates how to use the SubAgentsProvider to delegate work to sub-agents.
+// This sample demonstrates how to use the BackgroundAgentsProvider to delegate work to background agents.
 // A parent agent is given a list of stock tickers and instructed to find the closing price
-// for each ticker on December 31, 2025. It delegates the web searches to a sub-agent.
+// for each ticker on December 31, 2025. It delegates the web searches to a background agent.
 // The HarnessAgent provides built-in WebSearch (HostedWebSearchTool) so no manual web search
-// tool configuration is needed on the sub-agent.
+// tool configuration is needed on the background agent.
 //
 // Special commands:
 //   /exit    — End the session.
@@ -26,7 +26,7 @@
 const int MaxContextWindowTokens = 1_050_000;
 const int MaxOutputTokens = 128_000;
 
-// --- Sub-agent: Web Search Agent ---
+// --- Background agent: Web Search Agent ---
 // This agent uses the HarnessAgent's built-in HostedWebSearchTool to search the web.
 // Features not needed by this sub-agent are disabled.
 AIAgent webSearchAgent =
@@ -55,26 +55,26 @@
     });
 
 // --- Parent agent: Stock Price Researcher ---
-// This agent orchestrates the sub-agent to look up stock prices in parallel.
+// This agent orchestrates the background agent to look up stock prices in parallel.
 var parentInstructions =
     """
-    You are a stock price research assistant. You have access to a web search sub-agent that can look up information on the web.
+    You are a stock price research assistant. You have access to a web search background agent that can look up information on the web.
 
     When given a list of stock tickers, your job is to find the closing price for each ticker on December 31, 2025.
 
     ## Workflow
 
-    1. For each ticker, start a sub-task on the WebSearchAgent asking it to find the closing price on December 31, 2025.
-       - Start all sub-tasks before waiting for any of them to complete, so they run concurrently.
-    2. Wait for all sub-tasks to complete.
-    3. Retrieve the results from each sub-task.
+    1. For each ticker, start a background task on the WebSearchAgent asking it to find the closing price on December 31, 2025.
+       - Start all background tasks before waiting for any of them to complete, so they run concurrently.
+    2. Wait for all background tasks to complete.
+    3. Retrieve the results from each background task.
     4. Present a summary table with the ticker symbol and closing price for each stock.
     5. Clear all completed tasks to free memory.
 
     ## Important
 
-    - Always delegate web searches to the WebSearchAgent sub-agent. Do not try to answer from memory.
-    - If a sub-task fails or returns unclear results, continue the task with a more specific query.
+    - Always delegate web searches to the WebSearchAgent background agent. Do not try to answer from memory.
+    - If a background task fails or returns unclear results, continue the task with a more specific query.
     - Present results in a clean markdown table format.
     """;
 
@@ -94,7 +94,7 @@ 5. Clear all completed tasks to free memory.
     .AsHarnessAgent(MaxContextWindowTokens, MaxOutputTokens, new HarnessAgentOptions
     {
         Name = "StockPriceResearcher",
-        Description = "An agent that researches stock prices using sub-agents.",
+        Description = "An agent that researches stock prices using background agents.",
         DisableTodoProvider = true,
         DisableAgentModeProvider = true,
         DisableFileMemory = true,   // If enabled, this would allow the agent to store memories as files in a directory associated with the current session
@@ -103,7 +103,7 @@ 5. Clear all completed tasks to free memory.
         DisableWebSearch = true,
         AIContextProviders =
         [
-            new SubAgentsProvider([webSearchAgent]),
+            new BackgroundAgentsProvider([webSearchAgent]),
         ],
         ChatOptions = new ChatOptions
         {

@@ -1,24 +1,24 @@
-# Harness Step 02 — SubAgents (Stock Price Research)
+# Harness Step 02 — BackgroundAgents (Stock Price Research)
 
-This sample demonstrates how to use the **SubAgentsProvider** to delegate work from a parent agent to sub-agents. Both agents use `HarnessAgent` for pre-configured function invocation, per-service-call persistence, and context-window compaction.
+This sample demonstrates how to use the **BackgroundAgentsProvider** to delegate work from a parent agent to background agents. Both agents use `HarnessAgent` for pre-configured function invocation, per-service-call persistence, and context-window compaction.
 
 ## What It Does
 
-A parent agent receives a list of stock tickers and uses a web-search sub-agent to find the closing price for each ticker on December 31, 2025. The sub-tasks run concurrently, and results are presented in a summary table.
+A parent agent receives a list of stock tickers and uses a web-search background agent to find the closing price for each ticker on December 31, 2025. The background tasks run concurrently, and results are presented in a summary table.
 
 ### Architecture
 
 ```
-┌─────────────────────────────────┐
-│     StockPriceResearcher        │
-│         (Parent Agent)          │
-│                                 │
-│  SubAgentsProvider              │
-│    ├─ SubAgents_StartTask       │
-│    ├─ SubAgents_WaitFor...      │
-│    ├─ SubAgents_GetTaskResults  │
-│    └─ ...                       │
-└────────────┬────────────────────┘
+┌────────────────────────────────────────┐
+│     StockPriceResearcher               │
+│         (Parent Agent)                 │
+│                                        │
+│  BackgroundAgentsProvider              │
+│    ├─ BackgroundAgents_StartTask       │
+│    ├─ BackgroundAgents_WaitFor...      │
+│    ├─ BackgroundAgents_GetTaskResults  │
+│    └─ ...                              │
+└────────────┬───────────────────────────┘
              │  delegates to
              ▼
 ┌─────────────────────────────────┐
@@ -40,7 +40,7 @@ A parent agent receives a list of stock tickers and uses a web-search sub-agent
 ## Running the Sample
 
 ```bash
-cd dotnet/samples/02-agents/Harness/Harness_Step02_Research_WithSubAgents
+cd dotnet/samples/02-agents/Harness/Harness_Step02_Research_WithBackgroundAgents
 dotnet run
 ```
 
@@ -50,4 +50,4 @@ When prompted, enter a list of stock tickers such as:
 BAC, MSFT, BA
 ```
 
-The parent agent will delegate each ticker lookup to the web search sub-agent concurrently and present the results in a table.
+The parent agent will delegate each ticker lookup to the web search background agent concurrently and present the results in a table.
@@ -7,5 +7,5 @@ Samples demonstrating the [Harness AIContextProviders](../../../src/Microsoft.Ag
 | Sample | Description |
 | --- | --- |
 | [Harness_Step01_Research](./Harness_Step01_Research/README.md) | Using a ChatClientAgent with TodoProvider and AgentModeProvider for research, showcasing planning mode and todo management |
-| [Harness_Step02_Research_WithSubAgents](./Harness_Step02_Research_WithSubAgents/README.md) | Using SubAgentsProvider to delegate stock price lookups to a web-search sub-agent concurrently |
+| [Harness_Step02_Research_WithBackgroundAgents](./Harness_Step02_Research_WithBackgroundAgents/README.md) | Using BackgroundAgentsProvider to delegate stock price lookups to a web-search background agent concurrently |
 | [Harness_Step03_DataProcessing](./Harness_Step03_DataProcessing/README.md) | Using FileAccessProvider to give an agent access to CSV data files for reading, analysis, and output generation |
@@ -74,9 +74,11 @@ private static JsonSerializerOptions CreateDefaultOptions()
     [JsonSerializable(typeof(TodoState))]
     [JsonSerializable(typeof(TodoItem))]
     [JsonSerializable(typeof(TodoItemInput))]
+    [JsonSerializable(typeof(TodoCompleteInput))]
     [JsonSerializable(typeof(List<int>), TypeInfoPropertyName = "IntList")]
     [JsonSerializable(typeof(List<TodoItem>), TypeInfoPropertyName = "TodoItemList")]
     [JsonSerializable(typeof(List<TodoItemInput>), TypeInfoPropertyName = "TodoItemInputList")]
+    [JsonSerializable(typeof(List<TodoCompleteInput>), TypeInfoPropertyName = "TodoCompleteInputList")]
 
     // AgentModeProvider types
     [JsonSerializable(typeof(AgentModeState))]
@@ -95,12 +97,12 @@ private static JsonSerializerOptions CreateDefaultOptions()
     [JsonSerializable(typeof(FileListEntry))]
     [JsonSerializable(typeof(List<FileListEntry>), TypeInfoPropertyName = "FileListEntryList")]
 
-    // SubAgentsProvider types
-    [JsonSerializable(typeof(SubAgentState))]
-    [JsonSerializable(typeof(SubAgentRuntimeState))]
-    [JsonSerializable(typeof(SubTaskInfo))]
-    [JsonSerializable(typeof(SubTaskStatus))]
-    [JsonSerializable(typeof(List<SubTaskInfo>), TypeInfoPropertyName = "SubTaskInfoList")]
+    // BackgroundAgentsProvider types
+    [JsonSerializable(typeof(BackgroundAgentState))]
+    [JsonSerializable(typeof(BackgroundAgentRuntimeState))]
+    [JsonSerializable(typeof(BackgroundTaskInfo))]
+    [JsonSerializable(typeof(BackgroundTaskStatus))]
+    [JsonSerializable(typeof(List<BackgroundTaskInfo>), TypeInfoPropertyName = "BackgroundTaskInfoList")]
 
     [ExcludeFromCodeCoverage]
     internal sealed partial class JsonContext : JsonSerializerContext;

@@ -7,15 +7,15 @@
 namespace Microsoft.Agents.AI;
 
 /// <summary>
-/// Holds non-serializable runtime references for in-flight sub-tasks within a single parent session.
+/// Holds non-serializable runtime references for in-flight background tasks within a single parent session.
 /// </summary>
 /// <remarks>
 /// Properties are marked with <see cref="JsonIgnoreAttribute"/> because <see cref="Task{TResult}"/>
 /// and <see cref="AgentSession"/> are not JSON-serializable. After deserialization (e.g., after a restart),
 /// a fresh empty instance is created and any previously-running tasks are marked as
-/// <see cref="SubTaskStatus.Lost"/> by <see cref="SubAgentsProvider"/>.
+/// <see cref="BackgroundTaskStatus.Lost"/> by <see cref="BackgroundAgentsProvider"/>.
 /// </remarks>
-internal sealed class SubAgentRuntimeState
+internal sealed class BackgroundAgentRuntimeState
 {
     /// <summary>
     /// Gets the mapping of task IDs to their in-flight <see cref="Task{AgentResponse}"/> instances.
@@ -24,9 +24,9 @@ internal sealed class SubAgentRuntimeState
     public Dictionary<int, Task<AgentResponse>> InFlightTasks { get; } = [];
 
     /// <summary>
-    /// Gets the mapping of task IDs to their sub-agent <see cref="AgentSession"/> instances,
+    /// Gets the mapping of task IDs to their background agent <see cref="AgentSession"/> instances,
     /// needed for <c>ContinueTask</c>.
     /// </summary>
     [JsonIgnore]
-    public Dictionary<int, AgentSession> SubTaskSessions { get; } = [];
+    public Dictionary<int, AgentSession> BackgroundTaskSessions { get; } = [];
 }
@@ -8,21 +8,21 @@
 namespace Microsoft.Agents.AI;
 
 /// <summary>
-/// Represents the serializable state of sub-tasks managed by the <see cref="SubAgentsProvider"/>,
+/// Represents the serializable state of background tasks managed by the <see cref="BackgroundAgentsProvider"/>,
 /// stored in the session's <see cref="AgentSessionStateBag"/>.
 /// </summary>
 [Experimental(DiagnosticIds.Experiments.AgentsAIExperiments)]
-internal sealed class SubAgentState
+internal sealed class BackgroundAgentState
 {
     /// <summary>
-    /// Gets or sets the next ID to assign to a new sub-task.
+    /// Gets or sets the next ID to assign to a new background task.
     /// </summary>
     [JsonPropertyName("nextTaskId")]
     public int NextTaskId { get; set; } = 1;
 
     /// <summary>
-    /// Gets the list of sub-task metadata entries.
+    /// Gets the list of background task metadata entries.
     /// </summary>
     [JsonPropertyName("tasks")]
-    public List<SubTaskInfo> Tasks { get; set; } = [];
+    public List<BackgroundTaskInfo> Tasks { get; set; } = [];
 }