Make tool callbacks optional across SDKs

dotnet/GitHub.Copilot.SDK.slnx

@@ -10,7 +10,4 @@
   <Folder Name="/test/">
     <Project Path="test/GitHub.Copilot.SDK.Test.csproj" />
   </Folder>
-  <Folder Name="/samples/">
-    <Project Path="samples/Chat.csproj" />
-  </Folder>
 </Solution>

dotnet/README.md

@@ -10,13 +10,18 @@ SDK for programmatic control of GitHub Copilot CLI.
 dotnet add package GitHub.Copilot.SDK
 ```
 
-## Run the Sample
+## Run the Samples
 
 Try the interactive chat sample (from the repo root):
 
 ```bash
-cd dotnet/samples
-dotnet run
+dotnet run --file dotnet/samples/Chat.cs
+```
+
+The manual permission/tool-result resume sample can be run the same way:
+
+```bash
+dotnet run --file dotnet/samples/ManualToolResume.cs
 ```
 
 ## Quick Start
@@ -28,7 +33,7 @@ using GitHub.Copilot.SDK;
 await using var client = new CopilotClient();
 await client.StartAsync();
 
-// Create a session (OnPermissionRequest is required)
+// Create a session (OnPermissionRequest is optional; ApproveAll allows every tool)
 await using var session = await client.CreateSessionAsync(new SessionConfig
 {
     Model = "gpt-5",
@@ -105,14 +110,14 @@ Create a new conversation session.
 - `SessionId` - Custom session ID
 - `Model` - Model to use ("gpt-5", "claude-sonnet-4.5", etc.)
 - `ReasoningEffort` - Reasoning effort level for models that support it ("low", "medium", "high", "xhigh"). Use `ListModelsAsync()` to check which models support this option.
-- `Tools` - Custom tools exposed to the CLI
+- `Tools` - Custom tool declarations exposed to the CLI. Declarations without an invocable `AIFunction` are left pending for manual resolution.
 - `SystemMessage` - System message customization
 - `AvailableTools` - List of tool names to allow
 - `ExcludedTools` - List of tool names to disable
 - `Provider` - Custom API provider configuration (BYOK)
 - `Streaming` - Enable streaming of response chunks (default: false)
 - `InfiniteSessions` - Configure automatic context compaction (see below)
-- `OnPermissionRequest` - **Required.** Handler called before each tool execution to approve or deny it. Use `PermissionHandler.ApproveAll` to allow everything, or provide a custom function for fine-grained control. See [Permission Handling](#permission-handling) section.
+- `OnPermissionRequest` - Optional handler called before each tool execution to approve or deny it. When omitted, permission requests are emitted as events and left pending for manual resolution. Use `PermissionHandler.ApproveAll` to allow everything, or provide a custom function for fine-grained control. See [Permission Handling](#permission-handling) section.
 - `OnUserInputRequest` - Handler for user input requests from the agent (enables ask_user tool). See [User Input Requests](#user-input-requests) section.
 - `Hooks` - Hook handlers for session lifecycle events. See [Session Hooks](#session-hooks) section.
 
@@ -122,7 +127,7 @@ Resume an existing session. Returns the session with `WorkspacePath` populated i
 
 **ResumeSessionConfig:**
 
-- `OnPermissionRequest` - **Required.** Handler called before each tool execution to approve or deny it. See [Permission Handling](#permission-handling) section.
+- `OnPermissionRequest` - Optional handler called before each tool execution to approve or deny it. See [Permission Handling](#permission-handling) section.
 
 ##### `PingAsync(string? message = null): Task<PingResponse>`
 
@@ -715,7 +720,7 @@ No extra dependencies — uses built-in `System.Diagnostics.Activity`.
 
 ## Permission Handling
 
-An `OnPermissionRequest` handler is **required** whenever you create or resume a session. The handler is called before the agent executes each tool (file writes, shell commands, custom tools, etc.) and must return a decision.
+An `OnPermissionRequest` handler is optional when you create or resume a session. When provided, it is called before the agent executes each tool (file writes, shell commands, custom tools, etc.) and returns a decision. When omitted, permission requests are emitted as events and left pending for the consumer to resolve with the pending permission RPC.
 
 ### Approve All (simplest)
 
@@ -778,7 +783,7 @@ var session = await client.CreateSessionAsync(new SessionConfig
 
 ### Resuming Sessions
 
-Pass `OnPermissionRequest` when resuming a session too — it is required:
+You may pass `OnPermissionRequest` when resuming a session too:
 
 ```csharp
 var session = await client.ResumeSessionAsync("session-id", new ResumeSessionConfig

dotnet/samples/Chat.cs

@@ -1,3 +1,5 @@
+#:project ../src/GitHub.Copilot.SDK.csproj
+
 using GitHub.Copilot.SDK;
 
 await using var client = new CopilotClient();

dotnet/samples/ManualToolResume.cs

@@ -0,0 +1,92 @@
+#:project ../src/GitHub.Copilot.SDK.csproj
+
+using System.ComponentModel;
+using GitHub.Copilot.SDK;
+using GitHub.Copilot.SDK.Rpc;
+using Microsoft.Extensions.AI;
+
+var tool = ManualToolDeclaration();
+
+// 1. Create a session with a declaration-only tool, then stop after the permission prompt.
+await using CopilotClient client1 = new();
+await using var session1 = await client1.CreateSessionAsync(new() { Tools = [tool] });
+
+// Subscribe before sending so the permission event cannot be missed.
+var permissionRequested = WaitForEventAsync<PermissionRequestedEvent>(session1);
+await session1.SendAsync(new MessageOptions
+{
+    Prompt = "Use the manual_resume_status tool with id 'alpha', then tell me the status.",
+});
+
+var permissionEvent = await permissionRequested;
+await client1.ForceStopAsync();
+
+await PauseAsync();
+
+// 2. Resume pending work and grant permission to invoke the tool.
+await using CopilotClient client2 = new();
+await using var session2 = await client2.ResumeSessionAsync(session1.SessionId, new()
+{
+    Tools = [tool],
+    ContinuePendingWork = true,
+});
+
+// Subscribe before approving so the external tool request cannot be missed.
+var toolRequested = WaitForEventAsync<ExternalToolRequestedEvent>(
+    session2,
+    evt => evt.Data.ToolName == "manual_resume_status");
+
+await session2.Rpc.Permissions.HandlePendingPermissionRequestAsync(
+    permissionEvent.Data.RequestId,
+    new PermissionDecisionApproveOnce());
+
+var toolEvent = await toolRequested;
+await client2.ForceStopAsync();
+
+await PauseAsync();
+
+// 3. Resume again and manually provide the pending tool result.
+await using var client3 = new CopilotClient();
+await using var session3 = await client3.ResumeSessionAsync(session1.SessionId, new ResumeSessionConfig
+{
+    Tools = [tool],
+    ContinuePendingWork = true,
+});
+
+var assistantMessage = WaitForEventAsync<AssistantMessageEvent>(session3);
+await session3.Rpc.Tools.HandlePendingToolCallAsync(
+    toolEvent.Data.RequestId,
+    result: "MANUAL_STATUS_READY");
+
+var answer = await assistantMessage;
+Console.WriteLine(answer.Data.Content);
+
+static Task PauseAsync()
+{
+    Console.WriteLine("Simulating time passing...\n");
+    return Task.Delay(TimeSpan.FromSeconds(1));
+}
+
+static AIFunctionDeclaration ManualToolDeclaration() =>
+    AIFunctionFactory.Create(
+        ([Description("Identifier to look up")] string id) => $"not used: {id}",
+        "manual_resume_status",
+        "Looks up a status value. The SDK consumer supplies the result manually.")
+    // Remove the invocable callback so the SDK leaves tool execution pending.
+    .AsDeclarationOnly();
+
+static async Task<T> WaitForEventAsync<T>(CopilotSession session, Func<T, bool>? predicate = null)
+    where T : SessionEvent
+{
+    var tcs = new TaskCompletionSource<T>(TaskCreationOptions.RunContinuationsAsynchronously);
+    IDisposable? subscription = null;
+    subscription = session.On(evt =>
+    {
+        if (evt is T typed && (predicate?.Invoke(typed) ?? true))
+        {
+            subscription?.Dispose();
+            tcs.TrySetResult(typed);
+        }
+    });
+    return await tcs.Task.WaitAsync(TimeSpan.FromMinutes(2));
+}

dotnet/src/Client.cs

@@ -508,7 +508,7 @@ private static (SystemMessageConfig? wireConfig, Dictionary<string, Func<string,
     /// <summary>
     /// Creates a new Copilot session with the specified configuration.
     /// </summary>
-    /// <param name="config">Configuration for the session, including the required <see cref="SessionConfig.OnPermissionRequest"/> handler.</param>
+    /// <param name="config">Configuration for the session.</param>
     /// <param name="cancellationToken">A <see cref="CancellationToken"/> that can be used to cancel the operation.</param>
     /// <returns>A task that resolves to provide the <see cref="CopilotSession"/>.</returns>
     /// <remarks>
@@ -532,13 +532,6 @@ private static (SystemMessageConfig? wireConfig, Dictionary<string, Func<string,
     /// </example>
     public async Task<CopilotSession> CreateSessionAsync(SessionConfig config, CancellationToken cancellationToken = default)
     {
-        if (config.OnPermissionRequest == null)
-        {
-            throw new ArgumentException(
-                "An OnPermissionRequest handler is required when creating a session. " +
-                "For example, to allow all permissions, use CreateSessionAsync(new() { OnPermissionRequest = PermissionHandler.ApproveAll });");
-        }
-
         var connection = await EnsureConnectedAsync(cancellationToken);
         var totalTimestamp = Stopwatch.GetTimestamp();
 
@@ -667,10 +660,9 @@ public async Task<CopilotSession> CreateSessionAsync(SessionConfig config, Cance
     /// Resumes an existing Copilot session with the specified configuration.
     /// </summary>
     /// <param name="sessionId">The ID of the session to resume.</param>
-    /// <param name="config">Configuration for the resumed session, including the required <see cref="ResumeSessionConfig.OnPermissionRequest"/> handler.</param>
+    /// <param name="config">Configuration for the resumed session.</param>
     /// <param name="cancellationToken">A <see cref="CancellationToken"/> that can be used to cancel the operation.</param>
     /// <returns>A task that resolves to provide the <see cref="CopilotSession"/>.</returns>
-    /// <exception cref="ArgumentException">Thrown when <see cref="ResumeSessionConfig.OnPermissionRequest"/> is not set.</exception>
     /// <exception cref="InvalidOperationException">Thrown when the session does not exist or the client is not connected.</exception>
     /// <remarks>
     /// This allows you to continue a previous conversation, maintaining all conversation history.
@@ -691,13 +683,6 @@ public async Task<CopilotSession> CreateSessionAsync(SessionConfig config, Cance
     /// </example>
     public async Task<CopilotSession> ResumeSessionAsync(string sessionId, ResumeSessionConfig config, CancellationToken cancellationToken = default)
     {
-        if (config.OnPermissionRequest == null)
-        {
-            throw new ArgumentException(
-                "An OnPermissionRequest handler is required when resuming a session. " +
-                "For example, to allow all permissions, use new() { OnPermissionRequest = PermissionHandler.ApproveAll }.");
-        }
-
         var connection = await EnsureConnectedAsync(cancellationToken);
         var totalTimestamp = Stopwatch.GetTimestamp();
 
@@ -1835,6 +1820,8 @@ public async ValueTask<ToolCallResponseV2> OnToolCallV2(string sessionId,
             var session = client.GetSession(sessionId) ?? throw new ArgumentException($"Unknown session {sessionId}");
             if (session.GetTool(toolName) is not { } tool)
             {
+                // Support for not providing the tool handler is only available in the v3+ model.
+                // For v2, it must have been provided.
                 return new ToolCallResponseV2(new ToolResultObject
                 {
                     TextResultForLlm = $"Tool '{toolName}' is not supported.",
@@ -1993,7 +1980,7 @@ internal record ToolDefinition(
         bool? OverridesBuiltInTool = null,
         bool? SkipPermission = null)
     {
-        public static ToolDefinition FromAIFunction(AIFunction function)
+        public static ToolDefinition FromAIFunction(AIFunctionDeclaration function)
         {
             var overrides = function.AdditionalProperties.TryGetValue("is_override", out var val) && val is true;
             var skipPerm = function.AdditionalProperties.TryGetValue("skip_permission", out var skipVal) && skipVal is true;

dotnet/src/Session.cs

@@ -419,17 +419,20 @@ private async Task ProcessEventsAsync()
     /// <summary>
     /// Registers custom tool handlers for this session.
     /// </summary>
-    /// <param name="tools">A collection of AI functions that can be invoked by the assistant.</param>
+    /// <param name="tools">A collection of AI function declarations available to the assistant.</param>
     /// <remarks>
-    /// Tools allow the assistant to execute custom functions. When the assistant invokes a tool,
-    /// the corresponding handler is called with the tool arguments.
+    /// Tools backed by an <see cref="AIFunction"/> are invoked automatically. Declaration-only tools are
+    /// left pending for the client to resolve via the external tool request event.
     /// </remarks>
-    internal void RegisterTools(ICollection<AIFunction> tools)
+    internal void RegisterTools(ICollection<AIFunctionDeclaration> tools)
     {
         _toolHandlers.Clear();
         foreach (var tool in tools)
         {
-            _toolHandlers.Add(tool.Name, tool);
+            if (tool.GetService<AIFunction>() is { } function)
+            {
+                _toolHandlers.Add(tool.Name, function);
+            }
         }
     }
 
@@ -451,7 +454,7 @@ internal void RegisterTools(ICollection<AIFunction> tools)
     /// When the assistant needs permission to perform certain actions (e.g., file operations),
     /// this handler is called to approve or deny the request.
     /// </remarks>
-    internal void RegisterPermissionHandler(PermissionRequestHandler handler)
+    internal void RegisterPermissionHandler(PermissionRequestHandler? handler)
     {
         _permissionHandler = handler;
     }

dotnet/src/Types.cs

@@ -2087,9 +2087,11 @@ protected SessionConfig(SessionConfig? other)
     public bool? EnableConfigDiscovery { get; set; }
 
     /// <summary>
-    /// Custom tool functions available to the language model during the session.
+    /// Custom tool declarations available to the language model during the session.
+    /// Declarations backed by an <see cref="AIFunction"/> are invoked automatically; declarations without one
+    /// are left for the client to handle via external tool request events.
     /// </summary>
-    public ICollection<AIFunction>? Tools { get; set; }
+    public ICollection<AIFunctionDeclaration>? Tools { get; set; }
     /// <summary>
     /// System message configuration for the session.
     /// </summary>
@@ -2352,9 +2354,11 @@ protected ResumeSessionConfig(ResumeSessionConfig? other)
     public string? Model { get; set; }
 
     /// <summary>
-    /// Custom tool functions available to the language model during the resumed session.
+    /// Custom tool declarations available to the language model during the resumed session.
+    /// Declarations backed by an <see cref="AIFunction"/> are invoked automatically; declarations without one
+    /// are left for the client to handle via external tool request events.
     /// </summary>
-    public ICollection<AIFunction>? Tools { get; set; }
+    public ICollection<AIFunctionDeclaration>? Tools { get; set; }
 
     /// <summary>
     /// System message configuration.

dotnet/test/E2E/ClientE2ETests.cs

@@ -181,27 +181,24 @@ public async Task Should_Report_Error_With_Stderr_When_CLI_Fails_To_Start(bool u
     [Theory]
     [InlineData(true)]   // stdio transport
     [InlineData(false)]  // TCP transport
-    public async Task Should_Throw_When_CreateSession_Called_Without_PermissionHandler(bool useStdio)
+    public async Task Should_Allow_CreateSession_Called_Without_PermissionHandler(bool useStdio)
     {
-        using var client = new CopilotClient(new CopilotClientOptions { UseStdio = useStdio });
-
-        var ex = await Assert.ThrowsAsync<ArgumentException>(() => client.CreateSessionAsync(new SessionConfig()));
+        await using var client = new CopilotClient(new CopilotClientOptions { UseStdio = useStdio });
+        await using var session = await client.CreateSessionAsync(new SessionConfig());
 
-        Assert.Contains("OnPermissionRequest", ex.Message);
-        Assert.Contains("is required", ex.Message);
+        Assert.NotNull(session.SessionId);
     }
 
     [Theory]
     [InlineData(true)]   // stdio transport
     [InlineData(false)]  // TCP transport
-    public async Task Should_Throw_When_ResumeSession_Called_Without_PermissionHandler(bool useStdio)
+    public async Task Should_Allow_ResumeSession_Called_Without_PermissionHandler(bool useStdio)
     {
-        using var client = new CopilotClient(new CopilotClientOptions { UseStdio = useStdio });
-
-        var ex = await Assert.ThrowsAsync<ArgumentException>(() => client.ResumeSessionAsync("some-session-id", new()));
+        await using var client = new CopilotClient(new CopilotClientOptions { UseStdio = useStdio });
+        await using var originalSession = await client.CreateSessionAsync(new SessionConfig());
+        await using var resumedSession = await client.ResumeSessionAsync(originalSession.SessionId, new());
 
-        Assert.Contains("OnPermissionRequest", ex.Message);
-        Assert.Contains("is required", ex.Message);
+        Assert.Equal(originalSession.SessionId, resumedSession.SessionId);
     }
 
     [Theory]