Add minimal chat samples for all SDK languages

dotnet/GitHub.Copilot.SDK.slnx

@@ -10,4 +10,7 @@
   <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

@@ -10,6 +10,15 @@ SDK for programmatic control of GitHub Copilot CLI.
 dotnet add package GitHub.Copilot.SDK
 ```
 
+## Run the Sample
+
+Try the interactive chat sample (from the repo root):
+
+```bash
+cd dotnet/samples
+dotnet run
+```
+
 ## Quick Start
 
 ```csharp

dotnet/samples/Chat.cs

@@ -0,0 +1,32 @@
+using GitHub.Copilot.SDK;
+
+await using var client = new CopilotClient();
+await using var session = await client.CreateSessionAsync();
+
+using var _ = session.On(evt =>
+{
+    Console.ForegroundColor = ConsoleColor.Blue;
+    switch (evt)
+    {
+        case AssistantReasoningEvent reasoning:
+            Console.WriteLine($"[reasoning: {reasoning.Data.Content}]");
+            break;
+        case ToolExecutionStartEvent tool:
+            Console.WriteLine($"[tool: {tool.Data.ToolName}]");
+            break;
+    }
+    Console.ResetColor();
+});
+
+Console.WriteLine("Chat with Copilot (Ctrl+C to exit)\n");
+
+while (true)
+{
+    Console.Write("You: ");
+    var input = Console.ReadLine()?.Trim();
+    if (string.IsNullOrEmpty(input)) continue;
+    Console.WriteLine();
+
+    var reply = await session.SendAndWaitAsync(new MessageOptions { Prompt = input });
+    Console.WriteLine($"\nAssistant: {reply?.Data.Content}\n");
+}

dotnet/samples/Chat.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\src\GitHub.Copilot.SDK.csproj" />
+  </ItemGroup>
+</Project>

dotnet/src/Client.cs

@@ -11,6 +11,7 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Net.Sockets;
+using System.Text;
 using System.Text.Json;
 using System.Text.Json.Serialization;
 using System.Text.RegularExpressions;
@@ -183,13 +184,13 @@ async Task<Connection> StartCoreAsync(CancellationToken ct)
             if (_optionsHost is not null && _optionsPort is not null)
             {
                 // External server (TCP)
-                result = ConnectToServerAsync(null, _optionsHost, _optionsPort, ct);
+                result = ConnectToServerAsync(null, _optionsHost, _optionsPort, null, ct);
             }
             else
             {
                 // Child process (stdio or TCP)
-                var (cliProcess, portOrNull) = await StartCliServerAsync(_options, _logger, ct);
-                result = ConnectToServerAsync(cliProcess, portOrNull is null ? null : "localhost", portOrNull, ct);
+                var (cliProcess, portOrNull, stderrBuffer) = await StartCliServerAsync(_options, _logger, ct);
+                result = ConnectToServerAsync(cliProcess, portOrNull is null ? null : "localhost", portOrNull, stderrBuffer, ct);
             }
 
             var connection = await result;
@@ -842,11 +843,33 @@ private void DispatchLifecycleEvent(SessionLifecycleEvent evt)
     }
 
     internal static async Task<T> InvokeRpcAsync<T>(JsonRpc rpc, string method, object?[]? args, CancellationToken cancellationToken)
+    {
+        return await InvokeRpcAsync<T>(rpc, method, args, null, cancellationToken);
+    }
+
+    internal static async Task<T> InvokeRpcAsync<T>(JsonRpc rpc, string method, object?[]? args, StringBuilder? stderrBuffer, CancellationToken cancellationToken)
     {
         try
         {
             return await rpc.InvokeWithCancellationAsync<T>(method, args, cancellationToken);
         }
+        catch (StreamJsonRpc.ConnectionLostException ex)
+        {
+            string? stderrOutput = null;
+            if (stderrBuffer is not null)
+            {
+                lock (stderrBuffer)
+                {
+                    stderrOutput = stderrBuffer.ToString().Trim();
+                }
+            }
+
+            if (!string.IsNullOrEmpty(stderrOutput))
+            {
+                throw new IOException($"CLI process exited unexpectedly.\nstderr: {stderrOutput}", ex);
+            }
+            throw new IOException($"Communication error with Copilot CLI: {ex.Message}", ex);
+        }
         catch (StreamJsonRpc.RemoteRpcException ex)
         {
             throw new IOException($"Communication error with Copilot CLI: {ex.Message}", ex);
@@ -868,7 +891,7 @@ private async Task VerifyProtocolVersionAsync(Connection connection, Cancellatio
     {
         var expectedVersion = SdkProtocolVersion.GetVersion();
         var pingResponse = await InvokeRpcAsync<PingResponse>(
-            connection.Rpc, "ping", [new PingRequest()], cancellationToken);
+            connection.Rpc, "ping", [new PingRequest()], connection.StderrBuffer, cancellationToken);
 
         if (!pingResponse.ProtocolVersion.HasValue)
         {
@@ -887,7 +910,7 @@ private async Task VerifyProtocolVersionAsync(Connection connection, Cancellatio
         }
     }
 
-    private static async Task<(Process Process, int? DetectedLocalhostTcpPort)> StartCliServerAsync(CopilotClientOptions options, ILogger logger, CancellationToken cancellationToken)
+    private static async Task<(Process Process, int? DetectedLocalhostTcpPort, StringBuilder StderrBuffer)> StartCliServerAsync(CopilotClientOptions options, ILogger logger, CancellationToken cancellationToken)
     {
         // Use explicit path or bundled CLI - no PATH fallback
         var cliPath = options.CliPath ?? GetBundledCliPath(out var searchedPath)
@@ -957,14 +980,19 @@ private async Task VerifyProtocolVersionAsync(Connection connection, Cancellatio
         var cliProcess = new Process { StartInfo = startInfo };
         cliProcess.Start();
 
-        // Forward stderr to logger
+        // Capture stderr for error messages and forward to logger
+        var stderrBuffer = new StringBuilder();
         _ = Task.Run(async () =>
         {
             while (cliProcess != null && !cliProcess.HasExited)
             {
                 var line = await cliProcess.StandardError.ReadLineAsync(cancellationToken);
                 if (line != null)
                 {
+                    lock (stderrBuffer)
+                    {
+                        stderrBuffer.AppendLine(line);
+                    }
                     logger.LogDebug("[CLI] {Line}", line);
                 }
             }
@@ -991,7 +1019,7 @@ private async Task VerifyProtocolVersionAsync(Connection connection, Cancellatio
             }
         }
 
-        return (cliProcess, detectedLocalhostTcpPort);
+        return (cliProcess, detectedLocalhostTcpPort, stderrBuffer);
     }
 
     private static string? GetBundledCliPath(out string searchedPath)
@@ -1035,7 +1063,7 @@ private static (string FileName, IEnumerable<string> Args) ResolveCliCommand(str
         return (cliPath, args);
     }
 
-    private async Task<Connection> ConnectToServerAsync(Process? cliProcess, string? tcpHost, int? tcpPort, CancellationToken cancellationToken)
+    private async Task<Connection> ConnectToServerAsync(Process? cliProcess, string? tcpHost, int? tcpPort, StringBuilder? stderrBuffer, CancellationToken cancellationToken)
     {
         Stream inputStream, outputStream;
         TcpClient? tcpClient = null;
@@ -1080,7 +1108,7 @@ private async Task<Connection> ConnectToServerAsync(Process? cliProcess, string?
 
         _rpc = new ServerRpc(rpc);
 
-        return new Connection(rpc, cliProcess, tcpClient, networkStream);
+        return new Connection(rpc, cliProcess, tcpClient, networkStream, stderrBuffer);
     }
 
     [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Using happy path from https://microsoft.github.io/vs-streamjsonrpc/docs/nativeAOT.html")]
@@ -1321,12 +1349,14 @@ private class Connection(
         JsonRpc rpc,
         Process? cliProcess, // Set if we created the child process
         TcpClient? tcpClient, // Set if using TCP
-        NetworkStream? networkStream) // Set if using TCP
+        NetworkStream? networkStream, // Set if using TCP
+        StringBuilder? stderrBuffer = null) // Captures stderr for error messages
     {
         public Process? CliProcess => cliProcess;
         public TcpClient? TcpClient => tcpClient;
         public JsonRpc Rpc => rpc;
         public NetworkStream? NetworkStream => networkStream;
+        public StringBuilder? StderrBuffer => stderrBuffer;
     }
 
     private static class ProcessArgumentEscaper

dotnet/test/ClientTests.cs

@@ -224,4 +224,27 @@ public async Task Should_Not_Throw_When_Disposing_Session_After_Stopping_Client(
 
         await client.StopAsync();
     }
+
+    [Fact]
+    public async Task Should_Report_Error_With_Stderr_When_CLI_Fails_To_Start()
+    {
+        var client = new CopilotClient(new CopilotClientOptions
+        {
+            CliArgs = new[] { "--nonexistent-flag-for-testing" },
+            UseStdio = true
+        });
+
+        var ex = await Assert.ThrowsAsync<IOException>(async () =>
+        {
+            await client.StartAsync();
+        });
+
+        var errorMessage = ex.Message;
+        // Verify we get the stderr output in the error message
+        Assert.Contains("stderr", errorMessage, StringComparison.OrdinalIgnoreCase);
+        Assert.Contains("nonexistent", errorMessage, StringComparison.OrdinalIgnoreCase);
+
+        // Cleanup - ForceStop should handle the disconnected state gracefully
+        try { await client.ForceStopAsync(); } catch { /* Expected */ }
+    }
 }

go/README.md

@@ -10,6 +10,15 @@ A Go SDK for programmatic access to the GitHub Copilot CLI.
 go get github.com/github/copilot-sdk/go
 ```
 
+## Run the Sample
+
+Try the interactive chat sample (from the repo root):
+
+```bash
+cd go/samples
+go run chat.go
+```
+
 ## Quick Start
 
 ```go

go/client.go

@@ -29,10 +29,12 @@ package copilot
 
 import (
 	"bufio"
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"net"
 	"os"
 	"os/exec"
@@ -85,6 +87,8 @@ type Client struct {
 	lifecycleHandlers      []SessionLifecycleHandler
 	typedLifecycleHandlers map[SessionLifecycleEventType][]SessionLifecycleHandler
 	lifecycleHandlersMux   sync.Mutex
+	stderrBuf              bytes.Buffer // captures CLI stderr for error messages
+	processDone            chan error   // signals when CLI process exits
 
 	// RPC provides typed server-scoped RPC methods.
 	// This field is nil until the client is connected via Start().
@@ -149,6 +153,9 @@ func NewClient(options *ClientOptions) *Client {
 		if options.CLIPath != "" {
 			opts.CLIPath = options.CLIPath
 		}
+		if len(options.CLIArgs) > 0 {
+			opts.CLIArgs = append([]string{}, options.CLIArgs...)
+		}
 		if options.Cwd != "" {
 			opts.Cwd = options.Cwd
 		}
@@ -1022,7 +1029,10 @@ func (c *Client) startCLIServer(ctx context.Context) error {
 		// Default to "copilot" in PATH if no embedded CLI is available and no custom path is set
 		cliPath = "copilot"
 	}
-	args := []string{"--headless", "--no-auto-update", "--log-level", c.options.LogLevel}
+
+	// Start with user-provided CLIArgs, then add SDK-managed args
+	args := append([]string{}, c.options.CLIArgs...)
+	args = append(args, "--headless", "--no-auto-update", "--log-level", c.options.LogLevel)
 
 	// Choose transport mode
 	if c.useStdio {
@@ -1087,21 +1097,32 @@ func (c *Client) startCLIServer(ctx context.Context) error {
 			return fmt.Errorf("failed to create stderr pipe: %w", err)
 		}
 
-		// Read stderr in background
+		// Read stderr in background, capturing for error messages
 		go func() {
-			scanner := bufio.NewScanner(stderr)
-			for scanner.Scan() {
-				// Optionally log stderr
-				// fmt.Fprintf(os.Stderr, "CLI stderr: %s\n", scanner.Text())
-			}
+			io.Copy(&c.stderrBuf, stderr)
 		}()
 
 		if err := c.process.Start(); err != nil {
 			return fmt.Errorf("failed to start CLI server: %w", err)
 		}
 
+		// Monitor process exit to signal pending requests
+		c.processDone = make(chan error, 1)
+		go func() {
+			err := c.process.Wait()
+			stderrOutput := strings.TrimSpace(c.stderrBuf.String())
+			if stderrOutput != "" {
+				c.processDone <- fmt.Errorf("CLI process exited: %v\nstderr: %s", err, stderrOutput)
+			} else if err != nil {
+				c.processDone <- fmt.Errorf("CLI process exited: %v", err)
+			} else {
+				c.processDone <- fmt.Errorf("CLI process exited unexpectedly")
+			}
+		}()
+
 		// Create JSON-RPC client immediately
 		c.client = jsonrpc2.NewClient(stdin, stdout)
+		c.client.SetProcessDone(c.processDone)
 		c.RPC = rpc.NewServerRpc(c.client)
 		c.setupNotificationHandler()
 		c.client.Start()

go/internal/e2e/client_test.go

@@ -1,6 +1,7 @@
 package e2e
 
 import (
+	"strings"
 	"testing"
 	"time"
 
@@ -225,4 +226,24 @@ func TestClient(t *testing.T) {
 
 		client.Stop()
 	})
+
+	t.Run("should report error with stderr when CLI fails to start", func(t *testing.T) {
+		client := copilot.NewClient(&copilot.ClientOptions{
+			CLIPath:  cliPath,
+			CLIArgs:  []string{"--nonexistent-flag-for-testing"},
+			UseStdio: copilot.Bool(true),
+		})
+		t.Cleanup(func() { client.ForceStop() })
+
+		err := client.Start(t.Context())
+		if err == nil {
+			t.Fatal("Expected Start to fail with invalid CLI args")
+		}
+
+		errStr := err.Error()
+		// Verify we get the stderr output in the error message
+		if !strings.Contains(errStr, "stderr") || !strings.Contains(errStr, "nonexistent") {
+			t.Errorf("Expected error to contain stderr output about invalid flag, got: %v", err)
+		}
+	})
 }