feat!: genesis-pinned operator set, server identity with an encrypted control link, key-less join codes; release key continuity

Join codes need no passkey touch and carry only public values (genesis
fingerprint, owner credentials, installer hashes). Nodes pin the genesis and
owners at enrollment and only follow passkey-signed operator set versions.
The panel's server key is listed in the set; pinned nodes require its
signature and run the control link under AES-256-GCM. Password sessions carry
no capabilities. The updater adopts a next_key from a signed manifest.

Bump version to 0.2.0. [CI SKIP]

backend/fleet/src/Fleet.Link/FleetLink.cs

@@ -66,6 +66,12 @@ public sealed class FleetLinkOptions
     public long MaxInflightBytes { get; init; } = 4 << 20;
 
     public Backoff Backoff { get; init; } = new();
+
+    /// <summary>
+    /// 校验服务器身份：<see cref="IServerVerifier.Required"/> 为真（节点固定的操作员集合里登记了服务器密钥）时，
+    /// 服务器必须在挑战里证明自己，之后这条链路用应用层加密；否则按旧的方式（没有固定信任根的节点）。
+    /// </summary>
+    public IServerVerifier? ServerVerifier { get; init; }
 }
 
 /// <summary>
@@ -77,6 +83,7 @@ public sealed class FleetLink
     private const string RpcPath = "/api/agent/v1/rpc";
 
     private readonly FleetLinkOptions _options;
+    private volatile bool _secure;
     private readonly RpcRouter<LinkContext> _router;
     private readonly Dictionary<string, IStateHandler> _handlers;
     private readonly TimeProvider _time;
@@ -153,6 +160,9 @@ public sealed class FleetLink
         }
     }
 
+    /// <summary>当前这条链路是不是应用层加密的（服务器证明了身份）。</summary>
+    public bool IsSecure => _secure && IsConnected;
+
     private async Task<string> RunOnceAsync(CancellationToken ct)
     {
         using var socket = new ClientWebSocket();
@@ -160,7 +170,7 @@ public sealed class FleetLink
         socket.Options.KeepAliveTimeout = TimeSpan.FromSeconds(20); // 对端 20 秒没有回 Pong 就判定连接已死
         var builder = new UriBuilder(_options.Server) { Scheme = _options.Server.Scheme == "https" ? "wss" : "ws", Path = RpcPath };
         await socket.ConnectAsync(builder.Uri, ct);
-        await using var transport = new WsTransport(socket, _options.MaxFrameBytes);
+        await using var transport = new SecureTransport(new WsTransport(socket, _options.MaxFrameBytes));
 
         string? failure = await AuthenticateAsync(transport, ct);
         if (failure is not null)
@@ -168,6 +178,8 @@ public sealed class FleetLink
             return failure;
         }
 
+        _secure = transport.Secure;
+
         var session = new RpcSession<LinkContext>(transport, _router, new LinkContext(this), _time);
         using CancellationTokenSource sessionCts = CancellationTokenSource.CreateLinkedTokenSource(ct);
         Task run = session.RunAsync(sessionCts.Token);
@@ -211,7 +223,7 @@ public sealed class FleetLink
     }
 
     /// <summary>挑战 → 签名 → 认证结果。失败返回原因；服务端禁用该节点时不再重试。</summary>
-    private async Task<string?> AuthenticateAsync(WsTransport transport, CancellationToken ct)
+    private async Task<string?> AuthenticateAsync(SecureTransport transport, CancellationToken ct)
     {
         using var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(15), _time);
         using CancellationTokenSource linked = CancellationTokenSource.CreateLinkedTokenSource(ct, timeout.Token);
@@ -222,9 +234,44 @@ public sealed class FleetLink
         }
 
         ChallengeParams nonce = challenge.Params.Value.Deserialize(FleetRpcContext.Default.ChallengeParams)!;
-        string signature = Convert.ToBase64String(_options.Identity.Sign(SignaturePurpose.Auth, _options.NodeId.Value, nonce.Nonce));
-        RpcMessage request = RpcMessage.Request(1, FleetMethods.Auth, new AuthParams { NodeId = _options.NodeId.Value, Signature = signature }, FleetRpcContext.Default.AuthParams);
-        await transport.SendAsync(new RpcFrame(FrameKind.Text, JsonSerializer.SerializeToUtf8Bytes(request, FleetRpcContext.Default.RpcMessage)), linked.Token);
+
+        // 固定了操作员集合、而集合里登记了服务器密钥：服务器必须证明自己，否则不继续，也不交出任何东西
+        EphemeralKey? ephemeral = null;
+        AuthParams authParams;
+        try
+        {
+            if (_options.ServerVerifier is { Required: true } verifier)
+            {
+                if (!TryDecodeBase64(nonce.ServerEphemeral, out byte[] serverEphemeral) || !TryDecodeBase64(nonce.ServerSignature, out byte[] serverSignature)
+                    || !verifier.Verify(nonce.Nonce, serverEphemeral, serverSignature))
+                {
+                    return "the server could not prove its identity (it is not the server your operator set authorizes)";
+                }
+
+                ephemeral = new EphemeralKey();
+                string serverEphemeralText = Convert.ToBase64String(serverEphemeral);
+                string nodeEphemeralText = Convert.ToBase64String(ephemeral.PublicKeySpki);
+                authParams = new AuthParams
+                {
+                    NodeId = _options.NodeId.Value,
+                    Signature = Convert.ToBase64String(_options.Identity.Sign(SignaturePurpose.AuthSecure, _options.NodeId.Value, nonce.Nonce, serverEphemeralText, nodeEphemeralText)),
+                    NodeEphemeral = nodeEphemeralText,
+                };
+                RpcMessage secureRequest = RpcMessage.Request(1, FleetMethods.Auth, authParams, FleetRpcContext.Default.AuthParams);
+                await transport.SendAsync(new RpcFrame(FrameKind.Text, JsonSerializer.SerializeToUtf8Bytes(secureRequest, FleetRpcContext.Default.RpcMessage)), linked.Token);
+                transport.Enable(LinkCipher.ForNode(ephemeral, serverEphemeral, nonce.Nonce));
+            }
+            else
+            {
+                authParams = new AuthParams { NodeId = _options.NodeId.Value, Signature = Convert.ToBase64String(_options.Identity.Sign(SignaturePurpose.Auth, _options.NodeId.Value, nonce.Nonce)) };
+                RpcMessage request = RpcMessage.Request(1, FleetMethods.Auth, authParams, FleetRpcContext.Default.AuthParams);
+                await transport.SendAsync(new RpcFrame(FrameKind.Text, JsonSerializer.SerializeToUtf8Bytes(request, FleetRpcContext.Default.RpcMessage)), linked.Token);
+            }
+        }
+        finally
+        {
+            ephemeral?.Dispose();
+        }
 
         while (true)
         {
@@ -259,7 +306,26 @@ public sealed class FleetLink
         }
     }
 
-    private static async Task<RpcMessage?> ReceiveMessageAsync(WsTransport transport, CancellationToken ct)
+    private static bool TryDecodeBase64(string? text, out byte[] data)
+    {
+        data = [];
+        if (string.IsNullOrEmpty(text))
+        {
+            return false;
+        }
+
+        try
+        {
+            data = Convert.FromBase64String(text);
+            return true;
+        }
+        catch (FormatException)
+        {
+            return false;
+        }
+    }
+
+    private static async Task<RpcMessage?> ReceiveMessageAsync(SecureTransport transport, CancellationToken ct)
     {
         RpcFrame? frame = await transport.ReceiveAsync(ct);
         return frame is { Kind: FrameKind.Text } f ? JsonSerializer.Deserialize(f.Data.Span, FleetRpcContext.Default.RpcMessage) : null;

backend/fleet/src/Fleet.Link/SecureTransport.cs

@@ -0,0 +1,57 @@
+using Fleet.Identity;
+using Fleet.Rpc;
+
+namespace Fleet.Link;
+
+/// <summary>
+/// 认证阶段是明文，认证通过之后换成应用层加密（<see cref="LinkCipher"/>）：此后每帧都是加密的二进制帧，明文帧一律拒绝。
+/// 认证阶段服务器的拒绝回复可能是明文（还没有协商好密钥），所以第一帧加密的回复到达之前允许一次明文文本帧。
+/// </summary>
+internal sealed class SecureTransport : IRpcTransport
+{
+    private readonly IRpcTransport _inner;
+    private LinkCipher? _cipher;
+    private bool _allowPlaintext = true;
+
+    public SecureTransport(IRpcTransport inner)
+    {
+        _inner = inner;
+    }
+
+    public bool Secure => _cipher is not null;
+
+    public void Enable(LinkCipher cipher) => _cipher = cipher;
+
+    public ValueTask SendAsync(RpcFrame frame, CancellationToken ct) =>
+        _cipher is null ? _inner.SendAsync(frame, ct) : _inner.SendAsync(new RpcFrame(FrameKind.Binary, _cipher.Seal((byte)frame.Kind, frame.Data.Span)), ct);
+
+    public async ValueTask<RpcFrame?> ReceiveAsync(CancellationToken ct)
+    {
+        RpcFrame? frame = await _inner.ReceiveAsync(ct);
+        if (frame is not { } received || _cipher is null)
+        {
+            return frame;
+        }
+
+        if (received.Kind == FrameKind.Binary && _cipher.TryOpen(received.Data.Span, out byte kind, out byte[] data))
+        {
+            _allowPlaintext = false;
+            return new RpcFrame((FrameKind)kind, data);
+        }
+
+        if (_allowPlaintext && received.Kind == FrameKind.Text)
+        {
+            return received; // 认证被拒绝时服务器还没有协商好密钥，回复是明文
+        }
+
+        throw new IOException("a frame on the secure link failed to authenticate");
+    }
+
+    public ValueTask CloseAsync(string reason, CancellationToken ct) => _inner.CloseAsync(reason, ct);
+
+    public async ValueTask DisposeAsync()
+    {
+        _cipher?.Dispose();
+        await _inner.DisposeAsync();
+    }
+}