.NET: [BREAKING] Harness: Switch FileAccess to opt-in

dotnet/samples/02-agents/Harness/Harness_Step01_Research/Program.cs

@@ -85,7 +85,6 @@ Track your sources — you will need them when presenting results.
         MaxOutputTokens = MaxOutputTokens,
         Name = "ResearchAgent",
         Description = "A research assistant that plans and executes research tasks.",
-        DisableFileAccess = true,                           // If enabled, this would allow the agent to read/write files in a working directory
         OpenTelemetrySourceName = TracingSourceName,        // Use our custom source name so spans are captured by the TracerProvider above.
         FileMemoryStore = new FileSystemAgentFileStore(     // Configure the file memory provider to store files in a local folder called "agent-files".
             Path.Combine(AppContext.BaseDirectory, "agent-files")),

dotnet/samples/02-agents/Harness/Harness_Step02_Research_WithBackgroundAgents/Program.cs

@@ -57,7 +57,6 @@
         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
-        DisableFileAccess = true,       // If enabled, this would allow the agent to read/write files in a working directory
         DisableToolAutoApproval = true, // If true, this disables the don't-ask-again approval functionality.
         ChatOptions = new ChatOptions
         {
@@ -107,7 +106,6 @@ 5. Clear all completed tasks to free memory.
         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
-        DisableFileAccess = true,       // If enabled, this would allow the agent to read/write files in a working directory
         DisableToolAutoApproval = true, // If true, this disables the don't-ask-again approval functionality.
         DisableWebSearch = true,
         BackgroundAgents = [webSearchAgent],

dotnet/samples/02-agents/Harness/Harness_Step03_DataProcessing/Program.cs

@@ -1,12 +1,12 @@
 // Copyright (c) Microsoft. All rights reserved.
 
-// This sample demonstrates how to use a HarnessAgent with the default FileAccessProvider
+// This sample demonstrates how to use a HarnessAgent with the FileAccessProvider
 // to give an agent access to a folder of CSV data files. The agent can read, analyze,
 // and extract information from the data, then write results back as new files.
 //
 // The sample includes a pre-populated `working/` folder with sales transaction data.
-// The HarnessAgent's default FileAccessProvider uses `{cwd}/working` as its working directory,
-// which matches this sample's folder layout.
+// File access is opt-in: setting HarnessAgentOptions.FileAccessStore enables the
+// FileAccessProvider, and this sample points it at the `working/` folder below the location of the executable.
 // Ask the agent to analyze the data, produce summaries, or create new output files.
 //
 // Special commands:

dotnet/samples/02-agents/Harness/Harness_Step03_DataProcessing/README.md

@@ -1,11 +1,11 @@
 # What this sample demonstrates
 
-This sample demonstrates how to use a `HarnessAgent` with the default `FileAccessProvider` to give an agent access to a folder of data files for reading, analyzing, and writing results. The `HarnessAgent` pre-configures function invocation, per-service-call chat history persistence, in-loop compaction, tool approval, and OpenTelemetry — so the sample only needs to supply the chat client, token limits, custom instructions, and opt out of unused features.
+This sample demonstrates how to use a `HarnessAgent` with the `FileAccessProvider` to give an agent access to a folder of data files for reading, analyzing, and writing results. The `HarnessAgent` pre-configures function invocation, per-service-call chat history persistence, in-loop compaction, tool approval, and OpenTelemetry — so the sample only needs to supply the chat client, token limits, custom instructions, a `FileAccessStore`, and opt out of unused features.
 
 Key features showcased:
 
 - **HarnessAgent** — a pre-configured agent that wraps a `ChatClientAgent` with function invocation, per-service-call persistence, and context-window compaction
-- **FileAccessProvider** — the HarnessAgent's default file access provider uses `{cwd}/working` as its working directory, matching this sample's `working/` folder
+- **FileAccessProvider** — file access is opt-in; setting `HarnessAgentOptions.FileAccessStore` to the sample's `working/` folder enables the provider's read/write tools
 - **CSV data processing** — the agent reads sales transaction data and performs analysis on demand
 - **Output file creation** — the agent can write summaries, filtered data, or reports back to the data folder
 - **Streaming output** — responses are streamed token-by-token for a natural experience

dotnet/samples/02-agents/Harness/Harness_Step04_CodeExecution/Program.cs

@@ -82,8 +82,9 @@ to solve problems precisely rather than guessing. You also have access to skills
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
 // latency issues, unintended credential probing, and potential security risks from fallback mechanisms.
 // Create the agent with ALL HarnessAgent features enabled plus Hyperlight CodeAct.
-// No Disable* flags are set — TodoProvider, AgentModeProvider, FileMemory, FileAccess,
-// ToolApproval, WebSearch, and AgentSkillsProvider are all active.
+// TodoProvider, AgentModeProvider, FileMemory, ToolApproval, WebSearch, and
+// AgentSkillsProvider are on by default. File access is opt-in, so it is enabled here by
+// supplying a FileAccessStore.
 AIAgent agent =
     new AIProjectClient(
         new Uri(endpoint),
@@ -101,6 +102,8 @@ to solve problems precisely rather than guessing. You also have access to skills
         OpenTelemetrySourceName = TracingSourceName,
         // Point the file memory at a local folder for persistent memory across sessions.
         FileMemoryStore = new FileSystemAgentFileStore(Path.Combine(AppContext.BaseDirectory, "agent-files")),
+        // Enable file access (opt-in) by rooting the file access tools at a local working folder.
+        FileAccessStore = new FileSystemAgentFileStore(Path.Combine(AppContext.BaseDirectory, "working")),
         // Add the HyperlightCodeActProvider so the agent can execute Python code in a sandbox.
         AIContextProviders = [codeAct],
         ChatOptions = new ChatOptions

dotnet/samples/02-agents/Harness/Harness_Step05_Loop/Program.cs

@@ -252,7 +252,6 @@ AIAgent CreateLeanHarnessAgent(
         DisableAgentModeProvider = true,
         DisableTodoProvider = disableTodoProvider,
         DisableFileMemory = true,
-        DisableFileAccess = true,
         DisableWebSearch = true,
         ToolApprovalAgentOptions = toolApprovalAgentOptions,
         ChatOptions = new ChatOptions

dotnet/src/Microsoft.Agents.AI.Harness/HarnessAgent.cs

@@ -43,13 +43,13 @@ namespace Microsoft.Agents.AI;
 /// <item><description><see cref="TodoProvider"/> — persistent todo list that the agent uses to track multi-step plans. Disable with <see cref="HarnessAgentOptions.DisableTodoProvider"/>.</description></item>
 /// <item><description><see cref="AgentModeProvider"/> — mode tracking (e.g., "plan" vs "execute") that the agent uses to structure its work. Disable with <see cref="HarnessAgentOptions.DisableAgentModeProvider"/>.</description></item>
 /// <item><description><see cref="FileMemoryProvider"/> — file-based session memory allowing the agent to persist notes and artifacts across turns. Disable with <see cref="HarnessAgentOptions.DisableFileMemory"/>.</description></item>
-/// <item><description><see cref="FileAccessProvider"/> — shared file access providing read/write tools for a working directory. Disable with <see cref="HarnessAgentOptions.DisableFileAccess"/>.</description></item>
 /// <item><description><see cref="AgentSkillsProvider"/> — discovers and loads skill definitions from the file system, enabling dynamic tool sets. Disable with <see cref="HarnessAgentOptions.DisableAgentSkillsProvider"/>.</description></item>
 /// </list>
 /// </para>
 /// <para>
 /// <strong>Optional context providers (enabled via <see cref="HarnessAgentOptions"/>):</strong>
 /// <list type="bullet">
+/// <item><description><see cref="FileAccessProvider"/> — shared file access providing read/write tools for a working directory. Enable by setting <see cref="HarnessAgentOptions.FileAccessStore"/>; configure via <see cref="HarnessAgentOptions.FileAccessProviderOptions"/>.</description></item>
 /// <item><description><see cref="BackgroundAgentsProvider"/> — enables delegation to background agents for parallel work. Enable by setting <see cref="HarnessAgentOptions.BackgroundAgents"/>.</description></item>
 /// <item><description><c>ShellEnvironmentProvider</c> — injects OS/shell/CWD information and a shell execution tool. Enable by setting <c>HarnessAgentOptions.ShellExecutor</c> (.NET only).</description></item>
 /// </list>
@@ -320,13 +320,9 @@ private static List<AIContextProvider> BuildContextProviders(HarnessAgentOptions
                 }));
         }
 
-        if (options?.DisableFileAccess is not true)
+        if (options?.FileAccessStore is AgentFileStore fileAccessStore)
         {
-            AgentFileStore fileAccessStore = options?.FileAccessStore
-                ?? new FileSystemAgentFileStore(
-                    Path.Combine(Directory.GetCurrentDirectory(), "working"));
-
-            providers.Add(new FileAccessProvider(fileAccessStore));
+            providers.Add(new FileAccessProvider(fileAccessStore, options.FileAccessProviderOptions));
         }
 
         if (options?.DisableAgentSkillsProvider is not true)

dotnet/src/Microsoft.Agents.AI.Harness/HarnessAgentOptions.cs

@@ -237,24 +237,24 @@ public sealed class HarnessAgentOptions
     public AgentFileStore? FileMemoryStore { get; set; }
 
     /// <summary>
-    /// Gets or sets a value indicating whether the <see cref="FileAccessProvider"/> is disabled.
+    /// Gets or sets the <see cref="AgentFileStore"/> that enables the <see cref="FileAccessProvider"/>.
     /// </summary>
     /// <remarks>
-    /// When <see langword="false"/> (the default), a <see cref="FileAccessProvider"/> is included in the
-    /// agent's context providers, using either <see cref="FileAccessStore"/> or a default
-    /// <see cref="FileSystemAgentFileStore"/> rooted at <c>{cwd}/working</c>.
+    /// File access is opt-in. When <see langword="null"/> (the default), no <see cref="FileAccessProvider"/>
+    /// is added and the agent has no file access tools. When set, a <see cref="FileAccessProvider"/> is
+    /// included in the agent's context providers, backed by the supplied store and configured with
+    /// <see cref="FileAccessProviderOptions"/> when provided.
     /// </remarks>
-    public bool DisableFileAccess { get; set; }
+    public AgentFileStore? FileAccessStore { get; set; }
 
     /// <summary>
-    /// Gets or sets a custom <see cref="AgentFileStore"/> for the <see cref="FileAccessProvider"/>.
+    /// Gets or sets the <see cref="FileAccessProviderOptions"/> used to configure the <see cref="FileAccessProvider"/>.
     /// </summary>
     /// <remarks>
-    /// When <see langword="null"/> and <see cref="DisableFileAccess"/> is <see langword="false"/>,
-    /// a default <see cref="FileSystemAgentFileStore"/> is created.
-    /// This property is ignored when <see cref="DisableFileAccess"/> is <see langword="true"/>.
+    /// This property is only used when <see cref="FileAccessStore"/> is set (file access is opt-in).
+    /// When <see langword="null"/>, the provider uses its default options.
     /// </remarks>
-    public AgentFileStore? FileAccessStore { get; set; }
+    public FileAccessProviderOptions? FileAccessProviderOptions { get; set; }
 
     /// <summary>
     /// Gets or sets a value indicating whether the <see cref="HostedWebSearchTool"/> is disabled.

dotnet/tests/Microsoft.Agents.AI.Harness.UnitTests/HarnessAgentOptionsTests.cs

@@ -32,7 +32,6 @@ public void DefaultPropertyValues()
         Assert.False(options.DisableToolAutoApproval);
         Assert.False(options.DisableApprovalNotRequiredFunctionBypassing);
         Assert.False(options.DisableFileMemory);
-        Assert.False(options.DisableFileAccess);
         Assert.False(options.DisableWebSearch);
         Assert.False(options.DisableTodoProvider);
         Assert.False(options.DisableAgentModeProvider);
@@ -42,6 +41,7 @@ public void DefaultPropertyValues()
         Assert.Null(options.MaximumIterationsPerRequest);
         Assert.Null(options.FileMemoryStore);
         Assert.Null(options.FileAccessStore);
+        Assert.Null(options.FileAccessProviderOptions);
         Assert.Null(options.AgentModeProviderOptions);
         Assert.Null(options.AgentSkillsSource);
         Assert.Null(options.BackgroundAgents);
@@ -63,6 +63,7 @@ public void PropertiesCanBeSetAndRetrieved()
         var contextProviders = new AIContextProvider[] { new TodoProvider() };
         var fileMemoryStore = new Mock<AgentFileStore>().Object;
         var fileAccessStore = new Mock<AgentFileStore>().Object;
+        var fileAccessOptions = new FileAccessProviderOptions();
         var agentModeOptions = new AgentModeProviderOptions();
         var skillsSource = new Mock<AgentSkillsSource>().Object;
         var backgroundAgents = new AIAgent[] { new Mock<AIAgent>().Object };
@@ -89,8 +90,8 @@ public void PropertiesCanBeSetAndRetrieved()
             DisableApprovalNotRequiredFunctionBypassing = true,
             DisableFileMemory = true,
             FileMemoryStore = fileMemoryStore,
-            DisableFileAccess = true,
             FileAccessStore = fileAccessStore,
+            FileAccessProviderOptions = fileAccessOptions,
             DisableWebSearch = true,
             DisableTodoProvider = true,
             DisableAgentModeProvider = true,
@@ -124,8 +125,8 @@ public void PropertiesCanBeSetAndRetrieved()
         Assert.True(options.DisableApprovalNotRequiredFunctionBypassing);
         Assert.True(options.DisableFileMemory);
         Assert.Same(fileMemoryStore, options.FileMemoryStore);
-        Assert.True(options.DisableFileAccess);
         Assert.Same(fileAccessStore, options.FileAccessStore);
+        Assert.Same(fileAccessOptions, options.FileAccessProviderOptions);
         Assert.True(options.DisableWebSearch);
         Assert.True(options.DisableTodoProvider);
         Assert.True(options.DisableAgentModeProvider);

dotnet/tests/Microsoft.Agents.AI.Harness.UnitTests/HarnessAgentTests.cs

@@ -32,7 +32,6 @@ public class HarnessAgentTests
         DisableToolAutoApproval = true,
         DisableOpenTelemetry = true,
         DisableFileMemory = true,
-        DisableFileAccess = true,
         DisableWebSearch = true,
         DisableTodoProvider = true,
         DisableAgentModeProvider = true,
@@ -1212,15 +1211,15 @@ public void FileMemoryProvider_UsesCustomStore()
     #region Feature: FileAccessProvider
 
     /// <summary>
-    /// Verify that FileAccessProvider is included in AIContextProviders by default.
+    /// Verify that FileAccessProvider is included in AIContextProviders when a FileAccessStore is provided.
     /// </summary>
     [Fact]
-    public void FileAccessProvider_IncludedByDefault()
+    public void FileAccessProvider_IncludedWhenStoreProvided()
     {
         // Arrange
         var chatClient = new Mock<IChatClient>().Object;
         var options = CreateAllDisabledOptions();
-        options.DisableFileAccess = false;
+        options.FileAccessStore = new Mock<AgentFileStore>().Object;
 
         // Act
         var agent = new HarnessAgent(chatClient, options);
@@ -1232,10 +1231,10 @@ public void FileAccessProvider_IncludedByDefault()
     }
 
     /// <summary>
-    /// Verify that FileAccessProvider is excluded when disabled.
+    /// Verify that FileAccessProvider is excluded by default (opt-in: no store provided).
     /// </summary>
     [Fact]
-    public void FileAccessProvider_ExcludedWhenDisabled()
+    public void FileAccessProvider_ExcludedByDefault()
     {
         // Arrange
         var chatClient = new Mock<IChatClient>().Object;
@@ -1262,7 +1261,6 @@ public void FileAccessProvider_UsesCustomStore()
         var chatClient = new Mock<IChatClient>().Object;
         var customStore = new Mock<AgentFileStore>().Object;
         var options = CreateAllDisabledOptions();
-        options.DisableFileAccess = false;
         options.FileAccessStore = customStore;
 
         // Act
@@ -1274,6 +1272,46 @@ public void FileAccessProvider_UsesCustomStore()
         Assert.Contains(innerAgent!.AIContextProviders!, p => p is FileAccessProvider);
     }
 
+    /// <summary>
+    /// Verify that FileAccessProviderOptions are honored: setting DisableWriteTools must remove the
+    /// write tools from the provider that HarnessAgent wires up, while the read-only tools remain.
+    /// </summary>
+    [Fact]
+    public async Task FileAccessProvider_UsesProvidedOptionsAsync()
+    {
+        // Arrange
+        var chatClient = new Mock<IChatClient>().Object;
+        var options = CreateAllDisabledOptions();
+        options.FileAccessStore = new InMemoryAgentFileStore();
+        options.FileAccessProviderOptions = new FileAccessProviderOptions { DisableWriteTools = true };
+
+        // Act
+        var agent = new HarnessAgent(chatClient, options);
+        var innerAgent = agent.GetService<ChatClientAgent>();
+
+        // Assert — the FileAccessProvider is present and honors the supplied options.
+        Assert.NotNull(innerAgent?.AIContextProviders);
+        var fileAccessProvider = Assert.IsType<FileAccessProvider>(
+            Assert.Single(innerAgent!.AIContextProviders!, p => p is FileAccessProvider));
+
+        var mockAgent = new Mock<AIAgent>().Object;
+        var session = await agent.CreateSessionAsync();
+#pragma warning disable MAAI001
+        var context = new AIContextProvider.InvokingContext(mockAgent, session, new AIContext());
+#pragma warning restore MAAI001
+        AIContext result = await fileAccessProvider.InvokingAsync(context);
+        var toolNames = result.Tools!.OfType<AIFunction>().Select(t => t.Name).ToList();
+
+        // DisableWriteTools = true => only the read-only tools are exposed.
+        Assert.Contains(FileAccessProvider.ReadFileToolName, toolNames);
+        Assert.Contains(FileAccessProvider.LsToolName, toolNames);
+        Assert.Contains(FileAccessProvider.GrepToolName, toolNames);
+        Assert.DoesNotContain(FileAccessProvider.WriteToolName, toolNames);
+        Assert.DoesNotContain(FileAccessProvider.DeleteFileToolName, toolNames);
+        Assert.DoesNotContain(FileAccessProvider.ReplaceToolName, toolNames);
+        Assert.DoesNotContain(FileAccessProvider.ReplaceLinesToolName, toolNames);
+    }
+
     #endregion
 
     #region Feature: AgentSkillsProvider
@@ -1419,7 +1457,6 @@ public async Task AllDefaults_AllFeaturesEnabledAsync()
         Assert.Contains(providers, p => p is TodoProvider);
         Assert.Contains(providers, p => p is AgentModeProvider);
         Assert.Contains(providers, p => p is FileMemoryProvider);
-        Assert.Contains(providers, p => p is FileAccessProvider);
         Assert.Contains(providers, p => p is AgentSkillsProvider);
 
         // Assert — HostedWebSearchTool is present in the tools sent to the model
@@ -1903,7 +1940,6 @@ public void Constructor_LoggerFactoryIsUsedByDownstreamComponents()
             DisableToolAutoApproval = true,
             DisableOpenTelemetry = true,
             DisableFileMemory = true,
-            DisableFileAccess = true,
             DisableWebSearch = true,
             DisableTodoProvider = true,
             DisableAgentModeProvider = true,
@@ -1954,7 +1990,6 @@ public void Constructor_SucceedsWithoutTokenValues()
             DisableToolAutoApproval = true,
             DisableOpenTelemetry = true,
             DisableFileMemory = true,
-            DisableFileAccess = true,
             DisableWebSearch = true,
             DisableTodoProvider = true,
             DisableAgentModeProvider = true,
@@ -1986,7 +2021,6 @@ public void Constructor_SucceedsWithOnlyMaxContextWindowTokens()
             DisableToolAutoApproval = true,
             DisableOpenTelemetry = true,
             DisableFileMemory = true,
-            DisableFileAccess = true,
             DisableWebSearch = true,
             DisableTodoProvider = true,
             DisableAgentModeProvider = true,