.NET: Add a file memory provider

dotnet/Directory.Packages.props

@@ -75,6 +75,7 @@
     <PackageVersion Include="Microsoft.Extensions.Configuration.UserSecrets" Version="10.0.0" />
     <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="10.0.0" />
     <PackageVersion Include="Microsoft.Extensions.DependencyInjection.Abstractions" Version="10.0.6" />
+    <PackageVersion Include="Microsoft.Extensions.FileSystemGlobbing" Version="10.0.6" />
     <PackageVersion Include="Microsoft.Extensions.Hosting" Version="10.0.0" />
     <PackageVersion Include="Microsoft.Extensions.Http.Resilience" Version="10.0.0" />
     <PackageVersion Include="Microsoft.Extensions.Logging" Version="10.0.0" />

dotnet/samples/02-agents/Harness/Harness_Shared_Console/ToolCallFormatter.cs

@@ -41,6 +41,13 @@ public static string Format(FunctionCallContent call)
             "ContinueTask" => FormatContinueTask(call),
             "ClearCompletedTask" => FormatSingleId(call, "taskId"),
 
+            // File memory tools
+            "FileMemory_SaveFile" => FormatSaveFile(call),
+            "FileMemory_ReadFile" => FormatStringArg(call, "fileName"),
+            "FileMemory_DeleteFile" => FormatStringArg(call, "fileName"),
+            "FileMemory_ListFiles" => null,
+            "FileMemory_SearchFiles" => FormatSearchFiles(call),
+
             // External tools
             "web_search" => FormatStringArg(call, "query"),
             "DownloadUri" => FormatStringArg(call, "uri"),
@@ -152,6 +159,36 @@ public static string Format(FunctionCallContent call)
             : $"(task #{taskId.Value})";
     }
 
+    private static string? FormatSaveFile(FunctionCallContent call)
+    {
+        string? fileName = GetString(call, "fileName");
+        string? description = GetString(call, "description");
+
+        if (fileName is null)
+        {
+            return null;
+        }
+
+        return string.IsNullOrEmpty(description)
+            ? $"({fileName})"
+            : $"({fileName}, with description)";
+    }
+
+    private static string? FormatSearchFiles(FunctionCallContent call)
+    {
+        string? pattern = GetString(call, "regexPattern");
+        string? filePattern = GetString(call, "filePattern");
+
+        if (pattern is null)
+        {
+            return null;
+        }
+
+        return string.IsNullOrEmpty(filePattern)
+            ? $"(/{pattern}/)"
+            : $"(/{pattern}/ in {filePattern})";
+    }
+
     private static string? FormatStringArg(FunctionCallContent call, string paramName)
     {
         string? value = GetString(call, paramName);

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

@@ -90,7 +90,7 @@ This rule applies even when the answer seems obvious or the task seems small.
     {
         Name = "ResearchAgent",
         Description = "A research assistant that plans and executes research tasks.",
-        AIContextProviders = [new TodoProvider(), new AgentModeProvider()],
+        AIContextProviders = [new TodoProvider(), new AgentModeProvider(), new FileMemoryProvider(new InMemoryAgentFileStore())],
         ChatHistoryProvider = new InMemoryChatHistoryProvider(new InMemoryChatHistoryProviderOptions
         {
             ChatReducer = compactionStrategy.AsChatReducer(),

dotnet/src/Microsoft.Agents.AI/AgentJsonUtilities.cs

@@ -81,6 +81,15 @@ private static JsonSerializerOptions CreateDefaultOptions()
     // AgentModeProvider types
     [JsonSerializable(typeof(AgentModeState))]
 
+    // FileMemoryProvider types
+    [JsonSerializable(typeof(FileMemoryState))]
+    [JsonSerializable(typeof(FileSearchResult))]
+    [JsonSerializable(typeof(List<FileSearchResult>), TypeInfoPropertyName = "FileSearchResultList")]
+    [JsonSerializable(typeof(FileSearchMatch))]
+    [JsonSerializable(typeof(List<FileSearchMatch>), TypeInfoPropertyName = "FileSearchMatchList")]
+    [JsonSerializable(typeof(FileListEntry))]
+    [JsonSerializable(typeof(List<FileListEntry>), TypeInfoPropertyName = "FileListEntryList")]
+
     [ExcludeFromCodeCoverage]
     internal sealed partial class JsonContext : JsonSerializerContext;
 }

dotnet/src/Microsoft.Agents.AI/Harness/FileMemory/AgentFileStore.cs

@@ -0,0 +1,128 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.FileSystemGlobbing;
+using Microsoft.Shared.DiagnosticIds;
+
+namespace Microsoft.Agents.AI;
+
+/// <summary>
+/// Provides an abstract base class for file storage operations.
+/// </summary>
+/// <remarks>
+/// <para>
+/// All paths are relative to an implementation-defined root. Implementations may map these
+/// paths to a local file system, in-memory store, remote blob storage, or other mechanisms.
+/// </para>
+/// <para>
+/// Paths use forward slashes as separators and must not escape the root (e.g., via <c>..</c> segments).
+/// It is up to each implementation to ensure that this is enforced.
+/// </para>
+/// </remarks>
+[Experimental(DiagnosticIds.Experiments.AgentsAIExperiments)]
+public abstract class AgentFileStore
+{
+    /// <summary>
+    /// Writes content to a file, creating or overwriting it.
+    /// </summary>
+    /// <param name="path">The relative path of the file to write.</param>
+    /// <param name="content">The content to write to the file.</param>
+    /// <param name="cancellationToken">A token to cancel the operation.</param>
+    /// <returns>A task representing the asynchronous operation.</returns>
+    public abstract Task WriteFileAsync(string path, string content, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Reads the content of a file.
+    /// </summary>
+    /// <param name="path">The relative path of the file to read.</param>
+    /// <param name="cancellationToken">A token to cancel the operation.</param>
+    /// <returns>The file content, or <see langword="null"/> if the file does not exist.</returns>
+    public abstract Task<string?> ReadFileAsync(string path, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Deletes a file.
+    /// </summary>
+    /// <param name="path">The relative path of the file to delete.</param>
+    /// <param name="cancellationToken">A token to cancel the operation.</param>
+    /// <returns><see langword="true"/> if the file was deleted; <see langword="false"/> if it did not exist.</returns>
+    public abstract Task<bool> DeleteFileAsync(string path, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Lists files in a directory.
+    /// </summary>
+    /// <param name="directory">The relative path of the directory to list. Use an empty string for the root.</param>
+    /// <param name="cancellationToken">A token to cancel the operation.</param>
+    /// <returns>A list of file names in the specified directory (direct children only).</returns>
+    public abstract Task<IReadOnlyList<string>> ListFilesAsync(string directory, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Checks whether a file exists.
+    /// </summary>
+    /// <param name="path">The relative path of the file to check.</param>
+    /// <param name="cancellationToken">A token to cancel the operation.</param>
+    /// <returns><see langword="true"/> if the file exists; otherwise, <see langword="false"/>.</returns>
+    public abstract Task<bool> FileExistsAsync(string path, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Searches for files whose content matches a regular expression pattern.
+    /// </summary>
+    /// <param name="directory">The relative path of the directory to search. Use an empty string for the root.</param>
+    /// <param name="regexPattern">
+    /// A regular expression pattern to match against file contents. The pattern is matched case-insensitively.
+    /// For example, <c>"error|warning"</c> matches lines containing "error" or "warning".
+    /// </param>
+    /// <param name="filePattern">
+    /// An optional glob pattern to filter which files are searched (e.g., <c>"*.md"</c>, <c>"research*"</c>).
+    /// When <see langword="null"/>, all files in the directory are searched.
+    /// Uses standard glob syntax from <see cref="Matcher"/>.
+    /// </param>
+    /// <param name="cancellationToken">A token to cancel the operation.</param>
+    /// <returns>A list of search results with matching file names, snippets, and matching lines.</returns>
+    public abstract Task<IReadOnlyList<FileSearchResult>> SearchFilesAsync(string directory, string regexPattern, string? filePattern = null, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Ensures a directory exists, creating it if necessary.
+    /// </summary>
+    /// <param name="path">The relative path of the directory to create.</param>
+    /// <param name="cancellationToken">A token to cancel the operation.</param>
+    /// <returns>A task representing the asynchronous operation.</returns>
+    public abstract Task CreateDirectoryAsync(string path, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Creates a <see cref="Matcher"/> for the specified glob pattern. Use the returned instance
+    /// to test multiple file names without allocating a new matcher for each one.
+    /// </summary>
+    /// <param name="filePattern">
+    /// The glob pattern to match against (e.g., <c>"*.md"</c>, <c>"research*"</c>).
+    /// </param>
+    /// <returns>A <see cref="Matcher"/> configured with the specified pattern.</returns>
+    protected static Matcher CreateGlobMatcher(string filePattern)
+    {
+        var matcher = new Matcher(System.StringComparison.OrdinalIgnoreCase);
+        matcher.AddInclude(filePattern);
+        return matcher;
+    }
+
+    /// <summary>
+    /// Determines whether a file name matches a pre-built glob <see cref="Matcher"/>.
+    /// </summary>
+    /// <param name="fileName">The file name to test (not a full path — just the name).</param>
+    /// <param name="matcher">
+    /// A pre-built <see cref="Matcher"/> to test against.
+    /// When <see langword="null"/>, this method returns <see langword="true"/> for any file name.
+    /// </param>
+    /// <returns><see langword="true"/> if the file name matches the pattern or if the matcher is <see langword="null"/>; otherwise, <see langword="false"/>.</returns>
+    protected static bool MatchesGlob(string fileName, Matcher? matcher)
+    {
+        if (matcher is null)
+        {
+            return true;
+        }
+
+        PatternMatchingResult result = matcher.Match(fileName);
+        return result.HasMatches;
+    }
+}

dotnet/src/Microsoft.Agents.AI/Harness/FileMemory/FileListEntry.cs

@@ -0,0 +1,27 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Diagnostics.CodeAnalysis;
+using System.Text.Json.Serialization;
+using Microsoft.Shared.DiagnosticIds;
+
+namespace Microsoft.Agents.AI;
+
+/// <summary>
+/// Represents a file entry returned by the <see cref="FileMemoryProvider"/> list files tool,
+/// containing the file name and an optional description.
+/// </summary>
+[Experimental(DiagnosticIds.Experiments.AgentsAIExperiments)]
+public sealed class FileListEntry
+{
+    /// <summary>
+    /// Gets or sets the name of the file.
+    /// </summary>
+    [JsonPropertyName("fileName")]
+    public string FileName { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Gets or sets the description of the file, or <see langword="null"/> if no description is available.
+    /// </summary>
+    [JsonPropertyName("description")]
+    public string? Description { get; set; }
+}