Launch managed SDK servers through the Rust runtime wrapper

dotnet/README.md

@@ -101,6 +101,11 @@ new CopilotClient(CopilotClientOptions? options = null)
 - `RuntimeConnection.ForTcp(port = 0, connectionToken?, path?, args?)` — spawns the runtime as a child process listening on a TCP port. `port = 0` auto-allocates; if a non-zero port is already in use, startup fails (no fallback). Use `CopilotClient.RuntimePort` after `StartAsync` to read the assigned port. `connectionToken` is required if other clients will connect via `RuntimeConnection.ForUri(...)`.
 - `RuntimeConnection.ForUri(url, connectionToken?)` — connects to an already-running runtime at `url` (e.g., `"localhost:8080"`). Does not spawn a process.
 
+Managed stdio and TCP connections use the bundled `copilot-runtime[.exe]` and
+adjacent `runtime.node` by default. An explicit connection path or
+`COPILOT_CLI_PATH` overrides the bundled runtime.
+Managed launch fails if the bundled wrapper pair is unavailable.
+
 #### Methods
 
 ##### `StartAsync(): Task`

dotnet/src/Client.cs

@@ -55,6 +55,7 @@
 /// </example>
 public sealed partial class CopilotClient : IDisposable, IAsyncDisposable
 {
+    private const string ExplicitBundledCliMarker = ".copilot-explicit-cli";
     /// <summary>
     /// Minimum protocol version this SDK can communicate with.
     /// </summary>
@@ -416,9 +417,19 @@
                         ffiArgs.Add("--remote");
                     }
 
+                    var explicitCliPath = System.Environment.GetEnvironmentVariable("COPILOT_CLI_PATH");
+                    if (string.IsNullOrEmpty(explicitCliPath))
+                    {
+                        explicitCliPath = null;
+                    }
+                    var ffiRuntimePath = explicitCliPath is null
+                        ? GetBundledNativePath(FfiRuntimeHost.GetRuntimeLibraryFileName(), out var searchedRuntime)
+                            ?? throw new InvalidOperationException(
+                                $"In-process FFI runtime library not found at '{searchedRuntime}'.")
+                        : ResolveRuntimePathForExplicitCli(explicitCliPath);
                     var ffiHost = FfiRuntimeHost.Create(
-                        ResolveCliPathForFfi(),
-                        GetNapiPrebuildsFolderOrThrow(),
+                        ffiRuntimePath,
+                        explicitCliPath,
                         ffiEnvironment,
                         ffiArgs,
                         _logger);
@@ -2215,17 +2226,19 @@
         var tcpConnection = _connection as TcpRuntimeConnection;
         var useStdio = _connection is StdioRuntimeConnection;
 
-        // Use explicit path, COPILOT_CLI_PATH env var (from the connection's
-        // Environment, options.Environment, or process env), or bundled runtime - no PATH fallback
-        var envCliPath =
-            (childProcessConnection.Environment is not null && childProcessConnection.Environment.TryGetValue("COPILOT_CLI_PATH", out var connEnvValue) ? connEnvValue : null)
-            ?? (options.Environment is not null && options.Environment.TryGetValue("COPILOT_CLI_PATH", out var envValue) ? envValue : null)
-            ?? System.Environment.GetEnvironmentVariable("COPILOT_CLI_PATH");
-        var cliPath = childProcessConnection.Path
-            ?? envCliPath
-            ?? GetBundledCliPath(out var searchedPath)
-            ?? throw new InvalidOperationException($"Copilot runtime not found at '{searchedPath}'. Ensure the SDK NuGet package was restored correctly or provide an explicit RuntimeConnection.ForStdio(path: ...) / RuntimeConnection.ForTcp(path: ...).");
-        var cliPathSource = childProcessConnection.Path is not null ? "Options" : envCliPath is not null ? "Environment" : "Bundled";
+        // Explicit CLI paths preserve the legacy launch contract. Otherwise use
+        // the bundled native runtime pair.
+        var configuredEnvironment = childProcessConnection.Environment ?? options.Environment;
+        var envCliPath = configuredEnvironment is not null
+            ? configuredEnvironment.TryGetValue("COPILOT_CLI_PATH", out var configuredCliPath) ? configuredCliPath : null
+            : System.Environment.GetEnvironmentVariable("COPILOT_CLI_PATH");
+        var launch = childProcessConnection.Path is not null
+            ? new RuntimeLaunch(childProcessConnection.Path, "Options")
+            : envCliPath is not null
+                ? new RuntimeLaunch(envCliPath, "Environment")
+                : GetBundledRuntimeLaunch();
+        var cliPath = launch.Executable;
+        var cliPathSource = launch.Source;
         var args = new List<string>();
 
         if (childProcessConnection.Args != null)
@@ -2407,7 +2420,11 @@
 
     private static string? GetBundledCliPath(out string searchedPath)
     {
-        var binaryName = OperatingSystem.IsWindows() ? "copilot.exe" : "copilot";
+        return GetBundledNativePath(OperatingSystem.IsWindows() ? "copilot.exe" : "copilot", out searchedPath);
+    }
+
+    private static string? GetBundledNativePath(string binaryName, out string searchedPath)
+    {
         // Always use portable RID (e.g., linux-x64) to match the build-time placement,
         // since distro-specific RIDs (e.g., ubuntu.24.04-x64) are normalized at build time.
         var rid = GetPortableRid()
@@ -2416,6 +2433,57 @@
         return File.Exists(searchedPath) ? searchedPath : null;
     }
 
+    private static RuntimeLaunch GetBundledRuntimeLaunch()
+    {
+        _ = GetBundledNativePath(
+            OperatingSystem.IsWindows() ? "copilot-runtime.exe" : "copilot-runtime",
+            out var searchedWrapper);
+        var directory = Path.GetDirectoryName(searchedWrapper)!;
+        var runtimeNode = Path.Combine(directory, "runtime.node");
+        var explicitCliMarker = Path.Combine(directory, ExplicitBundledCliMarker);
+        if (!File.Exists(searchedWrapper)
+            && !File.Exists(runtimeNode)
+            && File.Exists(explicitCliMarker)
+            && GetBundledCliPath(out _) is { } explicitCli)
+        {
+            return new RuntimeLaunch(explicitCli, "Bundled explicit CLI");
+        }
+        return ValidateRuntimePair(searchedWrapper, "Bundled runtime");
+    }
+
+    private static RuntimeLaunch ValidateRuntimePair(string wrapper, string source)
+    {
+        var runtimeNode = Path.Combine(Path.GetDirectoryName(Path.GetFullPath(wrapper))!, "runtime.node");
+        if (!File.Exists(wrapper))
+        {
+            throw new InvalidOperationException($"Copilot runtime wrapper not found at '{wrapper}'.");
+        }
+        if (!File.Exists(runtimeNode))
+        {
+            throw new InvalidOperationException(
+                $"Copilot runtime wrapper at '{wrapper}' is missing its adjacent runtime.node at '{runtimeNode}'.");
+        }
+        if (new FileInfo(wrapper).Length == 0 || new FileInfo(runtimeNode).Length == 0)
+        {
+            throw new InvalidOperationException("Copilot runtime wrapper and adjacent runtime.node must both be non-empty.");
+        }
+#if NET8_0_OR_GREATER
+        if (!OperatingSystem.IsWindows())
+        {
+            var mode = File.GetUnixFileMode(wrapper);
+            const UnixFileMode executeBits =
+                UnixFileMode.UserExecute | UnixFileMode.GroupExecute | UnixFileMode.OtherExecute;
+            if ((mode & executeBits) == 0)
+            {
+                File.SetUnixFileMode(wrapper, mode | executeBits);
+            }
+        }
+#endif
+        return new RuntimeLaunch(wrapper, source);
+    }
+
+    private sealed record RuntimeLaunch(string Executable, string Source);
+
     private static string? GetPortableRid()
     {
         string os;
@@ -2439,26 +2507,22 @@
         return arch != null ? $"{os}-{arch}" : null;
     }
 
-    private string ResolveCliPathForFfi()
+    private static string ResolveRuntimePathForExplicitCli(string cliPath)
     {
-        var envCliPath = _options.Environment is not null && _options.Environment.TryGetValue("COPILOT_CLI_PATH", out var envValue)
-            ? envValue
-            : System.Environment.GetEnvironmentVariable("COPILOT_CLI_PATH");
-        if (!string.IsNullOrEmpty(envCliPath))
+        var fullEntrypoint = Path.GetFullPath(cliPath);
+        var directory = Path.GetDirectoryName(fullEntrypoint)
+            ?? throw new InvalidOperationException($"Could not determine directory for '{cliPath}'.");
+        var flatLibraryPath = Path.Combine(directory, FfiRuntimeHost.GetRuntimeLibraryFileName());
+        if (File.Exists(flatLibraryPath))
         {
-            return envCliPath;
+            return flatLibraryPath;
         }
-
-        // Fall back to the bundled single-file CLI the same way stdio discovers it.
-        // It embeds its own Node and is spawned directly as `copilot --embedded-host`,
-        // with the sibling cdylib loaded in-process (FfiRuntimeHost.Create prefers the
-        // flat `libcopilot_runtime.so`/`copilot_runtime.dll` next to the CLI, falling
-        // back to the dev `prebuilds/<folder>/runtime.node` layout).
-        var bundled = GetBundledCliPath(out var searchedPath);
-        return bundled
-            ?? throw new InvalidOperationException(
-                "In-process FFI hosting requires the Copilot CLI. Set the COPILOT_CLI_PATH "
-                + $"environment variable, or ensure the bundled CLI is present (looked in '{searchedPath}').");
+        var prebuildsLibraryPath = Path.Combine(
+            directory, "prebuilds", GetNapiPrebuildsFolderOrThrow(), "runtime.node");
+        return File.Exists(prebuildsLibraryPath)
+            ? prebuildsLibraryPath
+            : throw new InvalidOperationException(
+                $"FFI runtime library not found. Looked for '{flatLibraryPath}' and '{prebuildsLibraryPath}'.");
     }
 
     /// <summary>

dotnet/src/FfiRuntimeHost.cs

@@ -17,11 +17,9 @@ namespace GitHub.Copilot;
 /// and communicating over stdio/TCP.
 /// </summary>
 /// <remarks>
-/// The Rust <c>host_start</c> export spawns the residual TypeScript worker itself —
-/// typically the packaged single-file CLI (<c>copilot --embedded-host</c>, which embeds
-/// its own Node) or, for dev, <c>node dist-cli/index.js --embedded-host</c> — so the .NET
-/// host never launches Node directly. JSON-RPC frames are pumped across the ABI: writes go
-/// to <c>connection_write</c>; inbound frames arrive on a native callback that feeds
+/// The Rust <c>host_start</c> export constructs the server synchronously in this
+/// process. JSON-RPC frames are pumped across the ABI: writes go to
+/// <c>connection_write</c>; inbound frames arrive on a native callback that feeds
 /// <see cref="ReceiveStream"/>.
 /// <para>
 /// The native interop layer has two implementations selected by target framework. On
@@ -41,7 +39,7 @@ internal sealed partial class FfiRuntimeHost : IDisposable
     private const string LibraryName = "copilot_runtime";
 
     private readonly ILogger _logger;
-    private readonly string _cliEntrypoint;
+    private readonly string? _cliEntrypoint;
     private readonly string _libraryPath;
     private readonly IReadOnlyDictionary<string, string>? _environment;
     private readonly IReadOnlyList<string> _args;
@@ -53,7 +51,7 @@ internal sealed partial class FfiRuntimeHost : IDisposable
     private uint _connectionId;
     private bool _disposed;
 
-    private FfiRuntimeHost(string libraryPath, string cliEntrypoint, IReadOnlyDictionary<string, string>? environment, IReadOnlyList<string> args, ILogger logger)
+    private FfiRuntimeHost(string libraryPath, string? cliEntrypoint, IReadOnlyDictionary<string, string>? environment, IReadOnlyList<string> args, ILogger logger)
     {
         _libraryPath = libraryPath;
         _cliEntrypoint = cliEntrypoint;
@@ -70,58 +68,42 @@ private FfiRuntimeHost(string libraryPath, string cliEntrypoint, IReadOnlyDictio
         ?? throw new InvalidOperationException("FfiRuntimeHost has not been started.");
 
     /// <summary>
-    /// Loads the cdylib next to the given CLI entrypoint and prepares the FFI host.
-    /// The entrypoint is either the packaged single-file CLI binary (e.g.
-    /// <c>runtimes/&lt;rid&gt;/native/copilot</c>) or, for dev, a <c>.js</c> file (e.g.
-    /// <c>dist-cli/index.js</c>) launched via <c>node</c>. The cdylib is resolved
-    /// relative to the entrypoint directory, preferring the flat, natural
-    /// shared-library name the .NET build emits (e.g. <c>libcopilot_runtime.so</c>)
-    /// and falling back to the dev tarball layout
-    /// <c>prebuilds/&lt;prebuildsFolder&gt;/runtime.node</c>, where
-    /// <paramref name="prebuildsFolder"/> is the napi-rs
-    /// <c>&lt;node-platform&gt;-&lt;arch&gt;</c> folder name (e.g. <c>win32-x64</c>).
+    /// Loads the runtime cdylib and prepares the FFI host.
     /// </summary>
-    public static FfiRuntimeHost Create(string cliEntrypoint, string prebuildsFolder, IReadOnlyDictionary<string, string>? environment, IReadOnlyList<string> args, ILogger logger)
+    public static FfiRuntimeHost Create(string libraryPath, string? cliEntrypoint, IReadOnlyDictionary<string, string>? environment, IReadOnlyList<string> args, ILogger logger)
     {
-        var fullEntrypoint = Path.GetFullPath(cliEntrypoint);
-        var distDir = Path.GetDirectoryName(fullEntrypoint)
-            ?? throw new InvalidOperationException($"Could not determine directory for '{cliEntrypoint}'.");
-
-        // Bundled .NET layout: flat, natural shared-library name next to the CLI.
-        var flatLibraryPath = Path.Combine(distDir, GetRuntimeLibraryFileName());
-        // Dev/tarball layout: dist-cli/prebuilds/<node-platform>-<arch>/runtime.node.
-        var prebuildsLibraryPath = Path.Combine(distDir, "prebuilds", prebuildsFolder, "runtime.node");
-
-        var libraryPath = File.Exists(flatLibraryPath) ? flatLibraryPath
-            : File.Exists(prebuildsLibraryPath) ? prebuildsLibraryPath
-            : throw new InvalidOperationException(
-                $"FFI runtime library not found. Looked for '{flatLibraryPath}' and '{prebuildsLibraryPath}'.");
-
-        PrepareNativeLibrary(libraryPath);
-        return new FfiRuntimeHost(libraryPath, fullEntrypoint, environment, args, logger);
+        var fullLibraryPath = Path.GetFullPath(libraryPath);
+        if (!File.Exists(fullLibraryPath))
+        {
+            throw new InvalidOperationException($"FFI runtime library not found at '{fullLibraryPath}'.");
+        }
+        PrepareNativeLibrary(fullLibraryPath);
+        return new FfiRuntimeHost(
+            fullLibraryPath,
+            cliEntrypoint is null ? null : Path.GetFullPath(cliEntrypoint),
+            environment,
+            args,
+            logger);
     }
 
     /// <summary>
     /// The natural platform shared-library file name for the runtime cdylib, as
     /// emitted by the .NET build (the .node file renamed to what the Rust cdylib
     /// would be called on this OS).
     /// </summary>
-    private static string GetRuntimeLibraryFileName()
+    internal static string GetRuntimeLibraryFileName()
     {
         if (OperatingSystem.IsWindows()) return "copilot_runtime.dll";
         if (OperatingSystem.IsMacOS()) return "libcopilot_runtime.dylib";
         return "libcopilot_runtime.so";
     }
 
     /// <summary>
-    /// Starts the in-process runtime: spawns the CLI worker via the Rust host,
-    /// waits for readiness, and opens the FFI JSON-RPC connection.
+    /// Starts the in-process Rust runtime and opens the FFI JSON-RPC connection.
     /// </summary>
     public async Task StartAsync(CancellationToken cancellationToken)
     {
-        // host_start blocks until the worker connects back and signals readiness
-        // (up to ~30s), and connection_open must run outside any async runtime, so
-        // perform the blocking FFI handshake on a background thread.
+        // Keep synchronous native startup off the caller's async context.
         await Task.Run(() =>
         {
             var argvJson = BuildArgvJson(_cliEntrypoint, _args);
@@ -131,7 +113,7 @@ await Task.Run(() =>
             if (_serverId == 0)
             {
                 throw new InvalidOperationException(
-                    $"copilot_runtime_host_start failed (library '{_libraryPath}', entrypoint '{_cliEntrypoint}').");
+                    $"copilot_runtime_host_start failed (library '{_libraryPath}').");
             }
 
             _connectionId = NativeOpenConnection(_serverId);
@@ -154,24 +136,22 @@ await Task.Run(() =>
         }
     }
 
-    private static byte[] BuildArgvJson(string cliEntrypoint, IReadOnlyList<string> args)
+    private static byte[] BuildArgvJson(string? cliEntrypoint, IReadOnlyList<string> args)
     {
-        // A .js entrypoint (dev / dist-cli) is launched via node; the packaged
-        // single-file CLI binary embeds its own Node and is invoked directly.
-        var isJsFile = cliEntrypoint.EndsWith(".js", StringComparison.OrdinalIgnoreCase);
         using var stream = new MemoryStream();
         using (var writer = new Utf8JsonWriter(stream))
         {
             writer.WriteStartArray();
-            if (isJsFile)
+            if (cliEntrypoint is not null)
             {
-                writer.WriteStringValue("node");
+                if (cliEntrypoint.EndsWith(".js", StringComparison.OrdinalIgnoreCase))
+                {
+                    writer.WriteStringValue("node");
+                }
+                writer.WriteStringValue(cliEntrypoint);
+                writer.WriteStringValue("--embedded-host");
+                writer.WriteStringValue("--no-auto-update");
             }
-            writer.WriteStringValue(cliEntrypoint);
-            writer.WriteStringValue("--embedded-host");
-            // Pin the worker to the bundled pkg matching the loaded cdylib, instead of
-            // drifting to a newer version under the user's ~/.copilot/pkg (ABI skew).
-            writer.WriteStringValue("--no-auto-update");
             foreach (var arg in args)
             {
                 writer.WriteStringValue(arg);

dotnet/src/Session.cs

@@ -977,7 +977,7 @@ private async Task ExecutePermissionAndRespondAsync(string requestId, Permission
         }
         catch (Exception ex)
         {
-            _logger.LogError(ex, "Permission handler or response delivery failed. SessionId={SessionId}, RequestId={RequestId}", SessionId, requestId);
+            LogPermissionHandlerOrDeliveryFailed(ex, SessionId, requestId);
             try
             {
                 await Rpc.Permissions.HandlePendingPermissionRequestAsync(requestId, PermissionDecision.UserNotAvailable());
@@ -1975,6 +1975,9 @@ await InvokeRpcAsync<object>(
     [LoggerMessage(Level = LogLevel.Debug, Message = "Failed to fetch tool metadata for {toolName}")]
     private partial void LogToolMetadataFetchFailed(Exception exception, string toolName);
 
+    [LoggerMessage(Level = LogLevel.Error, Message = "Permission handler or response delivery failed. SessionId={SessionId}, RequestId={RequestId}")]
+    private partial void LogPermissionHandlerOrDeliveryFailed(Exception exception, string sessionId, string requestId);
+
     internal record SendMessageRequest
     {
         public string SessionId { get; init; } = string.Empty;