Add SFTP tools with SCP fallback

AGENTS.md

@@ -30,10 +30,12 @@ The first implementation pass intentionally narrows the MVP:
 * .NET 10 stdio MCP server
 * `ssh_exec`
 * `terminal_start`, `terminal_write`, `terminal_read`, and `terminal_stop`
+* `sftp_list`, `sftp_get`, and `sftp_put`
 * SSH.NET-based SSH connections
 * Tool-supplied `host`, `username`, optional `port`, optional `keyPath`, and optional `keyPassphrase`
 * Default key discovery from `~/.ssh/id_ed25519`, `~/.ssh/id_ecdsa`, then `~/.ssh/id_rsa` when `keyPath` is omitted
-* No SSH agent, OpenSSH alias, `ssh -G`, ProxyJump, ProxyCommand, or SFTP support yet
+* SFTP first for file transfer; `sftp_get` and `sftp_put` silently fall back to SCP if SFTP is unavailable
+* No SSH agent, OpenSSH alias, `ssh -G`, ProxyJump, or ProxyCommand support yet
 * Basic audit logging and timeout enforcement
 
 ## Non-Goals
@@ -169,21 +171,21 @@ Priority order:
 
 ```text
 1. SFTP
-2. SCP fallback (optional future enhancement)
+2. SCP fallback for get/put
 ```
 
 The implementation must:
 
-* Validate SFTP subsystem availability during connection
-* Return structured capability errors if unavailable
-* Not silently downgrade to SCP
+* Use SFTP for directory listing
+* Use SFTP first for file get/put
+* Silently fall back to SCP for file get/put if SFTP is unavailable
 
 Example error:
 
 ```json
 {
   "error": "sftp_unavailable",
-  "message": "Remote host does not expose the SFTP subsystem.",
+  "message": "Remote host does not expose the SFTP subsystem for directory listing.",
   "scpFallbackAvailable": false
 }
 ```
@@ -243,7 +245,6 @@ Input:
 {
   "host": "prod-api.example.com",
   "username": "deploy",
-  "shell": "bash",
   "cols": 120,
   "rows": 40,
   "port": 22,
@@ -267,6 +268,7 @@ Requirements:
 * Maintain server-side session state
 * Support idle timeout cleanup
 * Use the same key-auth inputs and default key discovery as `ssh_exec`
+* Use the remote account's default shell; do not write shell setup commands into the PTY after startup
 
 ---
 
@@ -553,6 +555,9 @@ The MVP must include:
 * terminal_write
 * terminal_read
 * terminal_stop
+* sftp_list
+* sftp_get
+* sftp_put
 * basic audit logging
 
 ---

src/McpSsh.Server/Program.cs

@@ -1,5 +1,6 @@
 using McpSsh.Server;
 using McpSsh.Server.Audit;
+using McpSsh.Server.Sftp;
 using McpSsh.Server.Ssh;
 using McpSsh.Server.Terminal;
 using McpSsh.Server.Tools;
@@ -14,11 +15,13 @@ builder.Logging.ClearProviders();
 builder.Services.AddSingleton<ISystemClock, SystemClock>();
 builder.Services.AddSingleton<IFileSystem, LocalFileSystem>();
 builder.Services.AddSingleton<ISshKeyResolver, DefaultSshKeyResolver>();
+builder.Services.AddSingleton<ISshClientFactory, SshNetClientFactory>();
 builder.Services.AddSingleton<IAuditLogger, JsonLineAuditLogger>();
 builder.Services.AddSingleton<ISshCommandExecutor, SshNetCommandExecutor>();
 builder.Services.AddSingleton<SshExecService>();
 builder.Services.AddSingleton<ITerminalConnectionFactory, SshNetTerminalConnectionFactory>();
 builder.Services.AddSingleton<TerminalSessionManager>();
+builder.Services.AddSingleton<SftpService>();
 
 builder.Services
     .AddMcpServer()

src/McpSsh.Server/Sftp/SftpModels.cs

@@ -0,0 +1,22 @@
+namespace McpSsh.Server.Sftp;
+
+public sealed record SftpEntry(
+    string Name,
+    string Path,
+    string Type,
+    long Size,
+    DateTime ModifiedUtc);
+
+public sealed record SftpListResult(
+    IReadOnlyList<SftpEntry>? Entries,
+    string? Error = null,
+    string? Message = null,
+    bool ScpFallbackAvailable = false);
+
+public sealed record SftpTransferResult(
+    long BytesTransferred,
+    string? LocalPath,
+    string? RemotePath,
+    string TransferProtocol,
+    string? Error = null,
+    string? Message = null);

src/McpSsh.Server/Sftp/SftpService.cs

@@ -0,0 +1,418 @@
+using McpSsh.Server.Audit;
+using McpSsh.Server.Ssh;
+using Renci.SshNet.Common;
+
+namespace McpSsh.Server.Sftp;
+
+public sealed class SftpService
+{
+    public const int DefaultPort = 22;
+    public const long DefaultMaxTransferBytes = 100L * 1024 * 1024;
+    public const long MaxTransferBytesLimit = 10L * 1024 * 1024 * 1024;
+
+    private readonly ISshClientFactory _clientFactory;
+    private readonly IAuditLogger _auditLogger;
+    private readonly ISystemClock _clock;
+
+    public SftpService(ISshClientFactory clientFactory, IAuditLogger auditLogger, ISystemClock clock)
+    {
+        _clientFactory = clientFactory;
+        _auditLogger = auditLogger;
+        _clock = clock;
+    }
+
+    public Task<SftpListResult> ListAsync(
+        string host,
+        string username,
+        string remotePath,
+        int? port,
+        string? keyPath,
+        string? keyPassphrase,
+        CancellationToken cancellationToken)
+    {
+        var request = ValidateRequest(host, username, port, keyPath, keyPassphrase);
+        if (string.IsNullOrWhiteSpace(remotePath))
+        {
+            return Task.FromResult(new SftpListResult(null, "invalid_remote_path", "Remote path is required."));
+        }
+
+        return Task.Run(() =>
+        {
+            try
+            {
+                using var client = _clientFactory.CreateSftpClient(request);
+                client.Connect();
+                cancellationToken.ThrowIfCancellationRequested();
+
+                var entries = client
+                    .ListDirectory(remotePath)
+                    .Where(file => file.Name is not "." and not "..")
+                    .Select(file => new SftpEntry(
+                        file.Name,
+                        CombineRemotePath(remotePath, file.Name),
+                        file.IsDirectory ? "directory" : file.IsSymbolicLink ? "symlink" : "file",
+                        file.Length,
+                        file.LastWriteTimeUtc))
+                    .ToArray();
+
+                Log("sftp_list", request.Host, success: true, command: remotePath);
+                return new SftpListResult(entries);
+            }
+            catch (Exception ex) when (TryMapSshException(ex, out var error, out var message))
+            {
+                Log("sftp_list", request.Host, success: false, errorCode: error, message: message, command: remotePath);
+                return new SftpListResult(null, error, message, ScpFallbackAvailable: false);
+            }
+        }, cancellationToken);
+    }
+
+    public Task<SftpTransferResult> GetAsync(
+        string host,
+        string username,
+        string remotePath,
+        string localPath,
+        int? port,
+        string? keyPath,
+        string? keyPassphrase,
+        bool? overwrite,
+        long? maxBytes,
+        CancellationToken cancellationToken)
+    {
+        var request = ValidateRequest(host, username, port, keyPath, keyPassphrase);
+        var transfer = ValidateTransferPaths(remotePath, localPath, maxBytes);
+        var resolvedLocalPath = ResolveLocalPath(transfer.LocalPath);
+        var allowOverwrite = overwrite ?? false;
+
+        if (File.Exists(resolvedLocalPath) && !allowOverwrite)
+        {
+            return Task.FromResult(new SftpTransferResult(0, resolvedLocalPath, transfer.RemotePath, "none", "local_file_exists", "Local file already exists."));
+        }
+
+        return Task.Run(() =>
+        {
+            Directory.CreateDirectory(Path.GetDirectoryName(resolvedLocalPath) ?? Directory.GetCurrentDirectory());
+            var tempPath = Path.Combine(Path.GetDirectoryName(resolvedLocalPath) ?? Directory.GetCurrentDirectory(), $".{Path.GetFileName(resolvedLocalPath)}.{Guid.NewGuid():N}.tmp");
+
+            try
+            {
+                try
+                {
+                    var bytes = DownloadWithSftp(request, transfer.RemotePath, tempPath, transfer.MaxBytes, cancellationToken);
+                    MoveDownloadedFile(tempPath, resolvedLocalPath, allowOverwrite);
+                    Log("sftp_get", request.Host, success: true, command: transfer.RemotePath);
+                    return new SftpTransferResult(bytes, resolvedLocalPath, transfer.RemotePath, "sftp");
+                }
+                catch (Exception ex) when (IsSftpFallbackCandidate(ex))
+                {
+                    var bytes = DownloadWithScp(request, transfer.RemotePath, tempPath, transfer.MaxBytes, cancellationToken);
+                    MoveDownloadedFile(tempPath, resolvedLocalPath, allowOverwrite);
+                    Log("sftp_get", request.Host, success: true, command: transfer.RemotePath);
+                    return new SftpTransferResult(bytes, resolvedLocalPath, transfer.RemotePath, "scp");
+                }
+            }
+            catch (Exception ex) when (TryMapSshException(ex, out var error, out var message))
+            {
+                DeleteQuietly(tempPath);
+                Log("sftp_get", request.Host, success: false, errorCode: error, message: message, command: transfer.RemotePath);
+                return new SftpTransferResult(0, resolvedLocalPath, transfer.RemotePath, "none", error, message);
+            }
+        }, cancellationToken);
+    }
+
+    public Task<SftpTransferResult> PutAsync(
+        string host,
+        string username,
+        string localPath,
+        string remotePath,
+        int? port,
+        string? keyPath,
+        string? keyPassphrase,
+        bool? overwrite,
+        long? maxBytes,
+        CancellationToken cancellationToken)
+    {
+        return Task.Run(() =>
+        {
+            SshConnectionRequest? request = null;
+            string? resolvedLocalPath = null;
+            string? resolvedRemotePath = null;
+
+            try
+            {
+                request = ValidateRequest(host, username, port, keyPath, keyPassphrase);
+                var transfer = ValidateTransferPaths(remotePath, localPath, maxBytes);
+                resolvedRemotePath = transfer.RemotePath;
+                resolvedLocalPath = ResolveExistingLocalFile(transfer.LocalPath, transfer.MaxBytes);
+                var allowOverwrite = overwrite ?? false;
+
+                try
+                {
+                    var bytes = UploadWithSftp(request, resolvedLocalPath, resolvedRemotePath, allowOverwrite, cancellationToken);
+                    Log("sftp_put", request.Host, success: true, command: resolvedRemotePath);
+                    return new SftpTransferResult(bytes, resolvedLocalPath, resolvedRemotePath, "sftp");
+                }
+                catch (Exception ex) when (IsSftpFallbackCandidate(ex))
+                {
+                    var bytes = UploadWithScp(request, resolvedLocalPath, resolvedRemotePath, allowOverwrite, cancellationToken);
+                    Log("sftp_put", request.Host, success: true, command: resolvedRemotePath);
+                    return new SftpTransferResult(bytes, resolvedLocalPath, resolvedRemotePath, "scp");
+                }
+            }
+            catch (Exception ex) when (TryMapSshException(ex, out var error, out var message))
+            {
+                Log("sftp_put", request?.Host ?? host, success: false, errorCode: error, message: message, command: resolvedRemotePath ?? remotePath);
+                return new SftpTransferResult(0, resolvedLocalPath, resolvedRemotePath ?? remotePath, "none", error, message);
+            }
+        }, cancellationToken);
+    }
+
+    private long DownloadWithSftp(SshConnectionRequest request, string remotePath, string tempPath, long maxBytes, CancellationToken cancellationToken)
+    {
+        using var client = _clientFactory.CreateSftpClient(request);
+        client.Connect();
+        cancellationToken.ThrowIfCancellationRequested();
+
+        var attributes = client.GetAttributes(remotePath);
+        if (attributes.IsDirectory)
+        {
+            throw new SshToolException("remote_path_is_directory", "Remote path is a directory.");
+        }
+
+        if (attributes.Size > maxBytes)
+        {
+            throw new SshToolException("download_too_large", $"Remote file size {attributes.Size} exceeds the configured maximum of {maxBytes} bytes.");
+        }
+
+        using var output = File.Create(tempPath);
+        client.DownloadFile(remotePath, output);
+        return output.Length;
+    }
+
+    private long DownloadWithScp(SshConnectionRequest request, string remotePath, string tempPath, long maxBytes, CancellationToken cancellationToken)
+    {
+        using var client = _clientFactory.CreateScpClient(request);
+        client.Connect();
+        cancellationToken.ThrowIfCancellationRequested();
+
+        using var output = File.Create(tempPath);
+        client.Download(remotePath, output);
+        output.Flush();
+        if (output.Length > maxBytes)
+        {
+            throw new SshToolException("download_too_large", $"Downloaded file size {output.Length} exceeds the configured maximum of {maxBytes} bytes.");
+        }
+
+        return output.Length;
+    }
+
+    private long UploadWithSftp(SshConnectionRequest request, string localPath, string remotePath, bool overwrite, CancellationToken cancellationToken)
+    {
+        using var client = _clientFactory.CreateSftpClient(request);
+        client.Connect();
+        cancellationToken.ThrowIfCancellationRequested();
+
+        if (!overwrite && client.Exists(remotePath))
+        {
+            throw new SshToolException("remote_file_exists", "Remote file already exists.");
+        }
+
+        using var input = File.OpenRead(localPath);
+        client.UploadFile(input, remotePath, overwrite);
+        return input.Length;
+    }
+
+    private long UploadWithScp(SshConnectionRequest request, string localPath, string remotePath, bool overwrite, CancellationToken cancellationToken)
+    {
+        if (!overwrite && CheckRemoteExistsWithSsh(request, remotePath, cancellationToken))
+        {
+            throw new SshToolException("remote_file_exists", "Remote file already exists.");
+        }
+
+        using var client = _clientFactory.CreateScpClient(request);
+        client.Connect();
+        cancellationToken.ThrowIfCancellationRequested();
+
+        var file = new FileInfo(localPath);
+        client.Upload(file, remotePath);
+        return file.Length;
+    }
+
+    private bool CheckRemoteExistsWithSsh(SshConnectionRequest request, string remotePath, CancellationToken cancellationToken)
+    {
+        using var client = _clientFactory.CreateSshClient(request);
+        client.Connect();
+        cancellationToken.ThrowIfCancellationRequested();
+        using var command = client.CreateCommand($"test -e {RemoteShellCommand.Quote(remotePath)}");
+        command.Execute();
+        return command.ExitStatus == 0;
+    }
+
+    private static SshConnectionRequest ValidateRequest(string host, string username, int? port, string? keyPath, string? keyPassphrase)
+    {
+        if (string.IsNullOrWhiteSpace(host))
+        {
+            throw new SshToolException("invalid_host", "Host is required.");
+        }
+
+        if (string.IsNullOrWhiteSpace(username))
+        {
+            throw new SshToolException("invalid_username", "Username is required.");
+        }
+
+        var resolvedPort = port ?? DefaultPort;
+        if (resolvedPort is < 1 or > 65535)
+        {
+            throw new SshToolException("invalid_port", "Port must be between 1 and 65535.");
+        }
+
+        return new SshConnectionRequest(
+            host.Trim(),
+            username.Trim(),
+            resolvedPort,
+            string.IsNullOrWhiteSpace(keyPath) ? null : keyPath.Trim(),
+            string.IsNullOrEmpty(keyPassphrase) ? null : keyPassphrase);
+    }
+
+    private static (string RemotePath, string LocalPath, long MaxBytes) ValidateTransferPaths(string remotePath, string localPath, long? maxBytes)
+    {
+        if (string.IsNullOrWhiteSpace(remotePath))
+        {
+            throw new SshToolException("invalid_remote_path", "Remote path is required.");
+        }
+
+        if (string.IsNullOrWhiteSpace(localPath))
+        {
+            throw new SshToolException("invalid_local_path", "Local path is required.");
+        }
+
+        var resolvedMaxBytes = maxBytes ?? DefaultMaxTransferBytes;
+        if (resolvedMaxBytes is < 1 or > MaxTransferBytesLimit)
+        {
+            throw new SshToolException("invalid_max_bytes", $"maxBytes must be between 1 and {MaxTransferBytesLimit}.");
+        }
+
+        return (remotePath.Trim(), localPath.Trim(), resolvedMaxBytes);
+    }
+
+    private static string ResolveExistingLocalFile(string localPath, long maxBytes)
+    {
+        var resolved = ResolveLocalPath(localPath);
+        if (!File.Exists(resolved))
+        {
+            throw new SshToolException("local_file_not_found", "Local file does not exist.");
+        }
+
+        var file = new FileInfo(resolved);
+        if (file.Length > maxBytes)
+        {
+            throw new SshToolException("upload_too_large", $"Local file size {file.Length} exceeds the configured maximum of {maxBytes} bytes.");
+        }
+
+        return resolved;
+    }
+
+    private static string ResolveLocalPath(string localPath)
+    {
+        var expanded = ExpandHomeDirectory(localPath);
+        var fullPath = Path.GetFullPath(expanded);
+        var currentDirectory = Path.GetFullPath(Directory.GetCurrentDirectory());
+        if (!fullPath.StartsWith(currentDirectory + Path.DirectorySeparatorChar, StringComparison.Ordinal) &&
+            !string.Equals(fullPath, currentDirectory, StringComparison.Ordinal))
+        {
+            throw new SshToolException("unsafe_local_path", "Local paths must stay within the current working directory.");
+        }
+
+        return fullPath;
+    }
+
+    private static string ExpandHomeDirectory(string path)
+    {
+        if (path == "~")
+        {
+            return Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);
+        }
+
+        if (path.StartsWith("~/", StringComparison.Ordinal))
+        {
+            return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.UserProfile), path[2..]);
+        }
+
+        return path;
+    }
+
+    private static void MoveDownloadedFile(string tempPath, string targetPath, bool overwrite)
+    {
+        File.Move(tempPath, targetPath, overwrite);
+    }
+
+    private static void DeleteQuietly(string path)
+    {
+        try
+        {
+            if (File.Exists(path))
+            {
+                File.Delete(path);
+            }
+        }
+        catch
+        {
+        }
+    }
+
+    private static bool IsSftpFallbackCandidate(Exception ex)
+    {
+        return ex is SshException or SftpPathNotFoundException or SftpPermissionDeniedException;
+    }
+
+    private static bool TryMapSshException(Exception ex, out string error, out string message)
+    {
+        switch (ex)
+        {
+            case SshToolException toolException:
+                error = toolException.ErrorCode;
+                message = toolException.Message;
+                return true;
+            case SshAuthenticationException:
+                error = "ssh_authentication_failed";
+                message = "SSH key authentication failed. Check the username, key path, and key passphrase.";
+                return true;
+            case SftpPermissionDeniedException:
+                error = "permission_denied";
+                message = ex.Message;
+                return true;
+            case SftpPathNotFoundException:
+                error = "path_not_found";
+                message = ex.Message;
+                return true;
+            case SshConnectionException:
+            case SshException:
+                error = "ssh_error";
+                message = ex.Message;
+                return true;
+            case IOException:
+            case UnauthorizedAccessException:
+                error = "file_error";
+                message = ex.Message;
+                return true;
+            default:
+                error = "transfer_error";
+                message = ex.Message;
+                return true;
+        }
+    }
+
+    private static string CombineRemotePath(string directory, string name)
+    {
+        if (directory.EndsWith('/'))
+        {
+            return directory + name;
+        }
+
+        return directory + "/" + name;
+    }
+
+    private void Log(string tool, string? host, bool success, string? errorCode = null, string? message = null, string? command = null)
+    {
+        _auditLogger.Log(new AuditEvent(_clock.UtcNow, tool, host, null, command, success, 0, errorCode, message));
+    }
+}

src/McpSsh.Server/Ssh/SshClientFactory.cs

@@ -0,0 +1,70 @@
+using Renci.SshNet;
+
+namespace McpSsh.Server.Ssh;
+
+public interface ISshClientFactory
+{
+    SshClient CreateSshClient(SshConnectionRequest request);
+
+    SftpClient CreateSftpClient(SshConnectionRequest request);
+
+    ScpClient CreateScpClient(SshConnectionRequest request);
+}
+
+public sealed record SshConnectionRequest(
+    string Host,
+    string Username,
+    int Port,
+    string? KeyPath,
+    string? KeyPassphrase,
+    TimeSpan? Timeout = null);
+
+public sealed class SshNetClientFactory : ISshClientFactory
+{
+    private readonly ISshKeyResolver _keyResolver;
+
+    public SshNetClientFactory(ISshKeyResolver keyResolver)
+    {
+        _keyResolver = keyResolver;
+    }
+
+    public SshClient CreateSshClient(SshConnectionRequest request)
+    {
+        var client = new SshClient(CreateConnectionInfo(request));
+        ApplyTimeout(client, request.Timeout);
+        return client;
+    }
+
+    public SftpClient CreateSftpClient(SshConnectionRequest request)
+    {
+        var client = new SftpClient(CreateConnectionInfo(request));
+        ApplyTimeout(client, request.Timeout);
+        return client;
+    }
+
+    public ScpClient CreateScpClient(SshConnectionRequest request)
+    {
+        var client = new ScpClient(CreateConnectionInfo(request));
+        ApplyTimeout(client, request.Timeout);
+        return client;
+    }
+
+    private ConnectionInfo CreateConnectionInfo(SshConnectionRequest request)
+    {
+        var keyPath = _keyResolver.ResolveKeyPath(request.KeyPath);
+        var keyFile = string.IsNullOrEmpty(request.KeyPassphrase)
+            ? new PrivateKeyFile(keyPath)
+            : new PrivateKeyFile(keyPath, request.KeyPassphrase);
+
+        var auth = new PrivateKeyAuthenticationMethod(request.Username, keyFile);
+        return new ConnectionInfo(request.Host, request.Port, request.Username, auth);
+    }
+
+    private static void ApplyTimeout(BaseClient client, TimeSpan? timeout)
+    {
+        if (timeout is { } value)
+        {
+            client.ConnectionInfo.Timeout = value;
+        }
+    }
+}

src/McpSsh.Server/Ssh/SshCommandExecutor.cs

@@ -10,11 +10,11 @@ public interface ISshCommandExecutor
 
 public sealed class SshNetCommandExecutor : ISshCommandExecutor
 {
-    private readonly ISshKeyResolver _keyResolver;
+    private readonly ISshClientFactory _clientFactory;
 
-    public SshNetCommandExecutor(ISshKeyResolver keyResolver)
+    public SshNetCommandExecutor(ISshClientFactory clientFactory)
     {
-        _keyResolver = keyResolver;
+        _clientFactory = clientFactory;
     }
 
     public Task<SshExecResult> ExecuteAsync(SshExecRequest request, CancellationToken cancellationToken)
@@ -26,13 +26,13 @@ public sealed class SshNetCommandExecutor : ISshCommandExecutor
     {
         try
         {
-            var keyPath = _keyResolver.ResolveKeyPath(request.KeyPath);
-            using var keyFile = string.IsNullOrEmpty(request.KeyPassphrase)
-                ? new PrivateKeyFile(keyPath)
-                : new PrivateKeyFile(keyPath, request.KeyPassphrase);
-            using var client = new SshClient(request.Host, request.Port, request.Username, keyFile);
-
-            client.ConnectionInfo.Timeout = TimeSpan.FromSeconds(request.TimeoutSeconds);
+            using var client = _clientFactory.CreateSshClient(new SshConnectionRequest(
+                request.Host,
+                request.Username,
+                request.Port,
+                request.KeyPath,
+                request.KeyPassphrase,
+                TimeSpan.FromSeconds(request.TimeoutSeconds)));
             client.Connect();
 
             cancellationToken.ThrowIfCancellationRequested();

src/McpSsh.Server/Terminal/TerminalConnection.cs

@@ -21,22 +21,23 @@ public interface ITerminalConnectionFactory
 public sealed class SshNetTerminalConnectionFactory : ITerminalConnectionFactory
 {
     private const int ShellBufferSize = 16 * 1024;
-    private readonly ISshKeyResolver _keyResolver;
+    private readonly ISshClientFactory _clientFactory;
 
-    public SshNetTerminalConnectionFactory(ISshKeyResolver keyResolver)
+    public SshNetTerminalConnectionFactory(ISshClientFactory clientFactory)
     {
-        _keyResolver = keyResolver;
+        _clientFactory = clientFactory;
     }
 
     public ITerminalConnection Create(TerminalStartRequest request)
     {
         try
         {
-            var keyPath = _keyResolver.ResolveKeyPath(request.KeyPath);
-            var keyFile = string.IsNullOrEmpty(request.KeyPassphrase)
-                ? new PrivateKeyFile(keyPath)
-                : new PrivateKeyFile(keyPath, request.KeyPassphrase);
-            var client = new SshClient(request.Host, request.Port, request.Username, keyFile);
+            var client = _clientFactory.CreateSshClient(new SshConnectionRequest(
+                request.Host,
+                request.Username,
+                request.Port,
+                request.KeyPath,
+                request.KeyPassphrase));
 
             client.Connect();
 
@@ -48,7 +49,7 @@ public sealed class SshNetTerminalConnectionFactory : ITerminalConnectionFactory
                 height: 0,
                 bufferSize: ShellBufferSize);
 
-            return new SshNetTerminalConnection(client, stream, keyFile);
+            return new SshNetTerminalConnection(client, stream);
         }
         catch (SshAuthenticationException ex)
         {
@@ -64,13 +65,11 @@ public sealed class SshNetTerminalConnectionFactory : ITerminalConnectionFactory
     {
         private readonly SshClient _client;
         private readonly ShellStream _stream;
-        private readonly PrivateKeyFile _keyFile;
 
-        public SshNetTerminalConnection(SshClient client, ShellStream stream, PrivateKeyFile keyFile)
+        public SshNetTerminalConnection(SshClient client, ShellStream stream)
         {
             _client = client;
             _stream = stream;
-            _keyFile = keyFile;
         }
 
         public bool DataAvailable => _stream.DataAvailable;
@@ -89,7 +88,6 @@ public sealed class SshNetTerminalConnectionFactory : ITerminalConnectionFactory
         {
             _stream.Dispose();
             _client.Dispose();
-            _keyFile.Dispose();
         }
     }
 }

src/McpSsh.Server/Terminal/TerminalResults.cs

@@ -3,7 +3,6 @@ namespace McpSsh.Server.Terminal;
 public sealed record TerminalStartRequest(
     string Host,
     string Username,
-    string? Shell,
     int Cols,
     int Rows,
     int Port,

src/McpSsh.Server/Terminal/TerminalSessionManager.cs

@@ -34,7 +34,6 @@ public sealed class TerminalSessionManager : IDisposable
     public Task<TerminalStartResult> StartAsync(
         string host,
         string username,
-        string? shell,
         int? cols,
         int? rows,
         int? port,
@@ -43,7 +42,7 @@ public sealed class TerminalSessionManager : IDisposable
         int? idleTimeoutSeconds,
         CancellationToken cancellationToken)
     {
-        var request = ValidateStart(host, username, shell, cols, rows, port, keyPath, keyPassphrase, idleTimeoutSeconds);
+        var request = ValidateStart(host, username, cols, rows, port, keyPath, keyPassphrase, idleTimeoutSeconds);
         var started = _clock.UtcNow;
 
         try
@@ -59,19 +58,14 @@ public sealed class TerminalSessionManager : IDisposable
                 throw new SshToolException("terminal_session_conflict", "Unable to allocate a unique terminal session ID.");
             }
 
-            if (!string.IsNullOrWhiteSpace(request.Shell))
-            {
-                connection.Write($"exec {request.Shell}\n");
-            }
-
             session.ReaderTask = Task.Run(() => ReadLoopAsync(session), CancellationToken.None);
-            Log("terminal_start", request.Host, success: true, command: request.Shell);
+            Log("terminal_start", request.Host, success: true);
 
             return Task.FromResult(new TerminalStartResult(sessionId));
         }
         catch (SshToolException ex)
         {
-            Log("terminal_start", request.Host, success: false, errorCode: ex.ErrorCode, message: ex.Message, command: request.Shell);
+            Log("terminal_start", request.Host, success: false, errorCode: ex.ErrorCode, message: ex.Message);
             return Task.FromResult(new TerminalStartResult(null, ex.ErrorCode, ex.Message));
         }
     }
@@ -183,7 +177,7 @@ public sealed class TerminalSessionManager : IDisposable
         }
     }
 
-    private static TerminalStartRequest ValidateStart(string host, string username, string? shell, int? cols, int? rows, int? port, string? keyPath, string? keyPassphrase, int? idleTimeoutSeconds)
+    private static TerminalStartRequest ValidateStart(string host, string username, int? cols, int? rows, int? port, string? keyPath, string? keyPassphrase, int? idleTimeoutSeconds)
     {
         if (string.IsNullOrWhiteSpace(host))
         {
@@ -222,7 +216,6 @@ public sealed class TerminalSessionManager : IDisposable
         return new TerminalStartRequest(
             host.Trim(),
             username.Trim(),
-            string.IsNullOrWhiteSpace(shell) ? null : shell.Trim(),
             resolvedCols,
             resolvedRows,
             resolvedPort,

src/McpSsh.Server/Tools/SshTools.cs

@@ -1,4 +1,5 @@
 using System.ComponentModel;
+using McpSsh.Server.Sftp;
 using McpSsh.Server.Ssh;
 using McpSsh.Server.Terminal;
 using ModelContextProtocol.Server;
@@ -10,11 +11,13 @@ public sealed class SshTools
 {
     private readonly SshExecService _sshExecService;
     private readonly TerminalSessionManager _terminalSessionManager;
+    private readonly SftpService _sftpService;
 
-    public SshTools(SshExecService sshExecService, TerminalSessionManager terminalSessionManager)
+    public SshTools(SshExecService sshExecService, TerminalSessionManager terminalSessionManager, SftpService sftpService)
     {
         _sshExecService = sshExecService;
         _terminalSessionManager = terminalSessionManager;
+        _sftpService = sftpService;
     }
 
     [McpServerTool(Name = "ssh_exec", Destructive = true)]
@@ -38,7 +41,6 @@ public sealed class SshTools
     public Task<TerminalStartResult> StartTerminalAsync(
         [Description("Remote hostname or IP address. OpenSSH aliases are not supported in this vertical slice.")] string host,
         [Description("Remote SSH username.")] string username,
-        [Description("Optional shell to exec after PTY allocation, for example bash or sh.")] string? shell = null,
         [Description("Terminal columns. Defaults to 120.")] int? cols = null,
         [Description("Terminal rows. Defaults to 40.")] int? rows = null,
         [Description("Remote SSH port. Defaults to 22.")] int? port = null,
@@ -47,7 +49,7 @@ public sealed class SshTools
         [Description("Idle timeout in seconds. Defaults to 900.")] int? idleTimeoutSeconds = null,
         CancellationToken cancellationToken = default)
     {
-        return _terminalSessionManager.StartAsync(host, username, shell, cols, rows, port, keyPath, keyPassphrase, idleTimeoutSeconds, cancellationToken);
+        return _terminalSessionManager.StartAsync(host, username, cols, rows, port, keyPath, keyPassphrase, idleTimeoutSeconds, cancellationToken);
     }
 
     [McpServerTool(Name = "terminal_write", Destructive = true)]
@@ -75,4 +77,52 @@ public sealed class SshTools
     {
         return _terminalSessionManager.Stop(sessionId);
     }
+
+    [McpServerTool(Name = "sftp_list", Destructive = false)]
+    [Description("List remote directory contents over SFTP.")]
+    public Task<SftpListResult> ListSftpAsync(
+        [Description("Remote hostname or IP address. OpenSSH aliases are not supported in this vertical slice.")] string host,
+        [Description("Remote SSH username.")] string username,
+        [Description("Remote directory path to list.")] string remotePath,
+        [Description("Remote SSH port. Defaults to 22.")] int? port = null,
+        [Description("Optional local private key path. Defaults to ~/.ssh/id_ed25519, ~/.ssh/id_ecdsa, then ~/.ssh/id_rsa.")] string? keyPath = null,
+        [Description("Optional private key passphrase. Use only with trusted MCP clients.")] string? keyPassphrase = null,
+        CancellationToken cancellationToken = default)
+    {
+        return _sftpService.ListAsync(host, username, remotePath, port, keyPath, keyPassphrase, cancellationToken);
+    }
+
+    [McpServerTool(Name = "sftp_get", Destructive = false)]
+    [Description("Download a remote file using SFTP, silently falling back to SCP when SFTP is unavailable.")]
+    public Task<SftpTransferResult> GetSftpAsync(
+        [Description("Remote hostname or IP address. OpenSSH aliases are not supported in this vertical slice.")] string host,
+        [Description("Remote SSH username.")] string username,
+        [Description("Remote file path to download.")] string remotePath,
+        [Description("Local destination path. Must stay within the server working directory.")] string localPath,
+        [Description("Remote SSH port. Defaults to 22.")] int? port = null,
+        [Description("Optional local private key path. Defaults to ~/.ssh/id_ed25519, ~/.ssh/id_ecdsa, then ~/.ssh/id_rsa.")] string? keyPath = null,
+        [Description("Optional private key passphrase. Use only with trusted MCP clients.")] string? keyPassphrase = null,
+        [Description("Overwrite an existing local file. Defaults to false.")] bool? overwrite = null,
+        [Description("Maximum download size in bytes. Defaults to 104857600.")] long? maxBytes = null,
+        CancellationToken cancellationToken = default)
+    {
+        return _sftpService.GetAsync(host, username, remotePath, localPath, port, keyPath, keyPassphrase, overwrite, maxBytes, cancellationToken);
+    }
+
+    [McpServerTool(Name = "sftp_put", Destructive = true)]
+    [Description("Upload a local file using SFTP, silently falling back to SCP when SFTP is unavailable.")]
+    public Task<SftpTransferResult> PutSftpAsync(
+        [Description("Remote hostname or IP address. OpenSSH aliases are not supported in this vertical slice.")] string host,
+        [Description("Remote SSH username.")] string username,
+        [Description("Local file path to upload. Must stay within the server working directory.")] string localPath,
+        [Description("Remote destination file path.")] string remotePath,
+        [Description("Remote SSH port. Defaults to 22.")] int? port = null,
+        [Description("Optional local private key path. Defaults to ~/.ssh/id_ed25519, ~/.ssh/id_ecdsa, then ~/.ssh/id_rsa.")] string? keyPath = null,
+        [Description("Optional private key passphrase. Use only with trusted MCP clients.")] string? keyPassphrase = null,
+        [Description("Overwrite an existing remote file. Defaults to false.")] bool? overwrite = null,
+        [Description("Maximum upload size in bytes. Defaults to 104857600.")] long? maxBytes = null,
+        CancellationToken cancellationToken = default)
+    {
+        return _sftpService.PutAsync(host, username, localPath, remotePath, port, keyPath, keyPassphrase, overwrite, maxBytes, cancellationToken);
+    }
 }

tests/McpSsh.Tests/SftpServiceTests.cs

@@ -0,0 +1,75 @@
+using McpSsh.Server;
+using McpSsh.Server.Audit;
+using McpSsh.Server.Sftp;
+using McpSsh.Server.Ssh;
+using Renci.SshNet;
+
+namespace McpSsh.Tests;
+
+public sealed class SftpServiceTests
+{
+    [Fact]
+    public async Task PutAsync_ReturnsErrorWhenLocalFileIsOutsideWorkingDirectory()
+    {
+        var service = CreateService();
+
+        var result = await service.PutAsync("host", "user", "/tmp/file.txt", "/tmp/file.txt", null, null, null, null, null, CancellationToken.None);
+
+        Assert.Equal("unsafe_local_path", result.Error);
+    }
+
+    [Fact]
+    public async Task PutAsync_ReturnsErrorWhenLocalFileIsMissing()
+    {
+        var service = CreateService();
+
+        var result = await service.PutAsync("host", "user", "missing-file.txt", "/tmp/file.txt", null, null, null, null, null, CancellationToken.None);
+
+        Assert.Equal("local_file_not_found", result.Error);
+    }
+
+    [Fact]
+    public async Task GetAsync_ReturnsErrorWhenLocalFileExistsAndOverwriteIsFalse()
+    {
+        var path = Path.Combine("sftp-test-existing.txt");
+        await File.WriteAllTextAsync(path, "existing");
+        try
+        {
+            var service = CreateService();
+
+            var result = await service.GetAsync("host", "user", "/tmp/file.txt", path, null, null, null, overwrite: false, maxBytes: null, CancellationToken.None);
+
+            Assert.Equal("local_file_exists", result.Error);
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    private static SftpService CreateService()
+    {
+        return new SftpService(new ThrowingClientFactory(), new CapturingAuditLogger(), new FixedClock());
+    }
+
+    private sealed class ThrowingClientFactory : ISshClientFactory
+    {
+        public SshClient CreateSshClient(SshConnectionRequest request) => throw new NotSupportedException();
+
+        public SftpClient CreateSftpClient(SshConnectionRequest request) => throw new NotSupportedException();
+
+        public ScpClient CreateScpClient(SshConnectionRequest request) => throw new NotSupportedException();
+    }
+
+    private sealed class CapturingAuditLogger : IAuditLogger
+    {
+        public void Log(AuditEvent auditEvent)
+        {
+        }
+    }
+
+    private sealed class FixedClock : ISystemClock
+    {
+        public DateTimeOffset UtcNow => DateTimeOffset.Parse("2026-05-24T12:00:00Z");
+    }
+}

tests/McpSsh.Tests/TerminalSessionManagerTests.cs

@@ -8,11 +8,11 @@ namespace McpSsh.Tests;
 public sealed class TerminalSessionManagerTests
 {
     [Fact]
-    public async Task StartAsync_CreatesSessionAndExecsRequestedShell()
+    public async Task StartAsync_CreatesSessionWithoutWritingShellSetup()
     {
         using var manager = CreateManager(out var factory, out _);
 
-        var result = await manager.StartAsync(" prod-api ", " deploy ", "bash", null, null, null, "/keys/id", "secret", null, CancellationToken.None);
+        var result = await manager.StartAsync(" prod-api ", " deploy ", null, null, null, "/keys/id", "secret", null, CancellationToken.None);
 
         Assert.Null(result.Error);
         Assert.StartsWith("term_", result.SessionId);
@@ -21,14 +21,14 @@ public sealed class TerminalSessionManagerTests
         Assert.Equal("deploy", factory.Request.Username);
         Assert.Equal("/keys/id", factory.Request.KeyPath);
         Assert.Equal("secret", factory.Request.KeyPassphrase);
-        Assert.Contains("exec bash\n", factory.Connection.Writes);
+        Assert.Empty(factory.Connection.Writes);
     }
 
     [Fact]
     public async Task Write_SendsInputToActiveSession()
     {
         using var manager = CreateManager(out var factory, out _);
-        var start = await manager.StartAsync("prod-api", "deploy", null, null, null, null, null, null, null, CancellationToken.None);
+        var start = await manager.StartAsync("prod-api", "deploy", null, null, null, null, null, null, CancellationToken.None);
 
         var result = manager.Write(start.SessionId!, "uptime\n");
 
@@ -40,7 +40,7 @@ public sealed class TerminalSessionManagerTests
     public async Task Read_DrainsBufferedOutputAndReportsTruncation()
     {
         using var manager = CreateManager(out var factory, out _);
-        var start = await manager.StartAsync("prod-api", "deploy", null, null, null, null, null, null, null, CancellationToken.None);
+        var start = await manager.StartAsync("prod-api", "deploy", null, null, null, null, null, null, CancellationToken.None);
         factory.Connection.QueueOutput("abcdef");
 
         var first = await ReadUntilOutputAsync(manager, start.SessionId!, 3);
@@ -67,7 +67,7 @@ public sealed class TerminalSessionManagerTests
     public async Task Stop_DisposesAndRemovesSession()
     {
         using var manager = CreateManager(out var factory, out _);
-        var start = await manager.StartAsync("prod-api", "deploy", null, null, null, null, null, null, null, CancellationToken.None);
+        var start = await manager.StartAsync("prod-api", "deploy", null, null, null, null, null, null, CancellationToken.None);
 
         var result = manager.Stop(start.SessionId!);
         var writeAfterStop = manager.Write(start.SessionId!, "pwd\n");