fix: 重构 ssh agent forwarding 转发代理并修复资源残留

- 将 agent forwarding 从长持有本地 agent 连接改为按 uth-agent@openssh.com channel 动态建桥
- 新增 ssh-agent 可用性探测流程，区分 forwarding 探测与实际转发注册
- 重构 forwarding 注册接口，按连接超时创建本地 agent bridge，不再复用单个长期占用的 agent 连接
- 新增 sshAgentForwardProxy 与 sshAgentForwardBridge，显式管理活跃 agent bridge 生命周期
- 在远端 channel 单侧 EOF、bridge 关闭和 proxy.Close() 路径上主动关闭本地 agent 连接与 SSH channel，避免 goroutine 和 agent 句柄残留
- 保留现有 denied / unavailable / close-race 语义，并继续保证自动 forwarding 的 best-effort 行为
- 扩充 agent forwarding 回归测试，覆盖单次启用、禁用、denied、unavailable、close race、单侧 EOF 释放以及 proxy Close 主动回收活跃 bridge 等关键场景

agent_forward.go

@@ -4,7 +4,9 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"net"
 	"strings"
+	"sync"
 	"time"
 
 	"golang.org/x/crypto/ssh"
@@ -15,24 +17,53 @@ var requestSSHAgentForwarding = func(session *ssh.Session) error {
 	return sshagent.RequestAgentForwarding(session)
 }
 
-var routeSSHAgentForwarding = func(client *ssh.Client, keyring sshagent.Agent) error {
+const sshAgentChannelType = "auth-agent@openssh.com"
-	return sshagent.ForwardToAgent(client, keyring)
+
+var routeSSHAgentForwarding = func(client *ssh.Client, timeout time.Duration) (io.Closer, error) {
+	return startSSHAgentForwardProxy(client, timeout)
 }
 
-var newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+var probeSSHAgentForwarding = func(timeout time.Duration) error {
 	conn, err := dialSSHAgent(timeout)
 	if err != nil {
-		return nil, nil, wrapSSHAgentForwardingUnavailable(err)
+		return wrapSSHAgentForwardingUnavailable(err)
 	}
 	if conn == nil {
-		return nil, nil, wrapSSHAgentForwardingUnavailable(errors.New("empty agent connection"))
+		return wrapSSHAgentForwardingUnavailable(errors.New("empty agent connection"))
 	}
-	return sshagent.NewClient(conn), conn, nil
+	return conn.Close()
 }
 
 var errSSHAgentForwardingDenied = errors.New("ssh-agent forwarding request denied")
 var errSSHAgentForwardingUnavailable = errors.New("ssh-agent forwarding unavailable")
 
+type sshAgentForwardProxy struct {
+	stopOnce sync.Once
+	stopCh   chan struct{}
+
+	activeMu sync.Mutex
+	active   map[*sshAgentForwardBridge]struct{}
+}
+
+func (p *sshAgentForwardProxy) Close() error {
+	if p == nil {
+		return nil
+	}
+	p.stopOnce.Do(func() {
+		close(p.stopCh)
+	})
+	p.closeActive()
+	return nil
+}
+
+type sshAgentForwardBridge struct {
+	proxy   *sshAgentForwardProxy
+	channel ssh.Channel
+	conn    net.Conn
+
+	closeOnce sync.Once
+}
+
 func (s *StarSSH) RequestAgentForwarding(session *ssh.Session) error {
 	if s == nil {
 		return errors.New("ssh client is nil")
@@ -80,20 +111,21 @@ func (s *StarSSH) ensureAgentForwarding() error {
 		return err
 	}
 
-	keyring, closer, err := newSSHAgentForwarder(effectiveDialTimeout(s.LoginInfo))
+	timeout := effectiveDialTimeout(s.LoginInfo)
-	if err != nil {
+	if err := probeSSHAgentForwarding(timeout); err != nil {
 		return wrapSSHAgentForwardingUnavailable(err)
 	}
 	if s.closing.Load() {
-		_ = closer.Close()
 		return errSSHClientClosing
 	}
-	if err := routeSSHAgentForwarding(client, keyring); err != nil {
+	closer, err := routeSSHAgentForwarding(client, timeout)
-		_ = closer.Close()
+	if err != nil {
 		return err
 	}
 	if !s.canAttachAgentForwarder(client) {
-		_ = closer.Close()
+		if closer != nil {
+			_ = closer.Close()
+		}
 		return errSSHClientClosing
 	}
 	s.agentForwarder = closer
@@ -149,3 +181,175 @@ func wrapSSHAgentForwardingUnavailable(err error) error {
 	}
 	return fmt.Errorf("%w: %v", errSSHAgentForwardingUnavailable, err)
 }
+
+func startSSHAgentForwardProxy(client *ssh.Client, timeout time.Duration) (io.Closer, error) {
+	if client == nil {
+		return nil, errors.New("ssh client is nil")
+	}
+	channels := client.HandleChannelOpen(sshAgentChannelType)
+	if channels == nil {
+		return nil, errors.New("agent: already have handler for " + sshAgentChannelType)
+	}
+
+	proxy := &sshAgentForwardProxy{
+		stopCh: make(chan struct{}),
+		active: make(map[*sshAgentForwardBridge]struct{}),
+	}
+	go func() {
+		for {
+			select {
+			case <-proxy.stopCh:
+				return
+			case ch, ok := <-channels:
+				if !ok {
+					return
+				}
+				go handleSSHAgentForwardChannel(proxy, ch, timeout)
+			}
+		}
+	}()
+	return proxy, nil
+}
+
+func handleSSHAgentForwardChannel(proxy *sshAgentForwardProxy, ch ssh.NewChannel, timeout time.Duration) {
+	if ch == nil {
+		return
+	}
+	conn, err := dialSSHAgent(timeout)
+	if err != nil {
+		_ = ch.Reject(ssh.ConnectionFailed, err.Error())
+		return
+	}
+	if conn == nil {
+		_ = ch.Reject(ssh.ConnectionFailed, "ssh-agent connection unavailable")
+		return
+	}
+
+	channel, reqs, err := ch.Accept()
+	if err != nil {
+		_ = conn.Close()
+		return
+	}
+	go ssh.DiscardRequests(reqs)
+
+	bridge := &sshAgentForwardBridge{
+		proxy:   proxy,
+		channel: channel,
+		conn:    conn,
+	}
+	if !proxy.registerBridge(bridge) {
+		bridge.close()
+		return
+	}
+	go bridge.run()
+}
+
+func proxySSHAgentChannel(channel ssh.Channel, conn net.Conn) {
+	bridge := &sshAgentForwardBridge{
+		channel: channel,
+		conn:    conn,
+	}
+	bridge.run()
+}
+
+func (b *sshAgentForwardBridge) run() {
+	if b == nil {
+		return
+	}
+	defer b.unregister()
+
+	var wg sync.WaitGroup
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		_, _ = io.Copy(b.channel, b.conn)
+		b.close()
+	}()
+	go func() {
+		defer wg.Done()
+		_, _ = io.Copy(b.conn, b.channel)
+		b.close()
+	}()
+	wg.Wait()
+}
+
+func (b *sshAgentForwardBridge) close() {
+	if b == nil {
+		return
+	}
+	b.closeOnce.Do(func() {
+		closeWriter(b.channel)
+		closeWriter(b.conn)
+		if b.channel != nil {
+			_ = b.channel.Close()
+		}
+		if b.conn != nil {
+			_ = b.conn.Close()
+		}
+	})
+}
+
+func (b *sshAgentForwardBridge) unregister() {
+	if b == nil || b.proxy == nil {
+		return
+	}
+	b.proxy.unregisterBridge(b)
+}
+
+func (p *sshAgentForwardProxy) registerBridge(bridge *sshAgentForwardBridge) bool {
+	if p == nil || bridge == nil {
+		return false
+	}
+
+	p.activeMu.Lock()
+	defer p.activeMu.Unlock()
+
+	select {
+	case <-p.stopCh:
+		return false
+	default:
+	}
+	if p.active == nil {
+		p.active = make(map[*sshAgentForwardBridge]struct{})
+	}
+	p.active[bridge] = struct{}{}
+	return true
+}
+
+func (p *sshAgentForwardProxy) unregisterBridge(bridge *sshAgentForwardBridge) {
+	if p == nil || bridge == nil {
+		return
+	}
+
+	p.activeMu.Lock()
+	defer p.activeMu.Unlock()
+
+	delete(p.active, bridge)
+}
+
+func (p *sshAgentForwardProxy) closeActive() {
+	if p == nil {
+		return
+	}
+
+	p.activeMu.Lock()
+	active := make([]*sshAgentForwardBridge, 0, len(p.active))
+	for bridge := range p.active {
+		active = append(active, bridge)
+	}
+	p.active = make(map[*sshAgentForwardBridge]struct{})
+	p.activeMu.Unlock()
+
+	for _, bridge := range active {
+		bridge.close()
+	}
+}
+
+func closeWriter(value any) {
+	type closeWriter interface {
+		CloseWrite() error
+	}
+	if cw, ok := value.(closeWriter); ok {
+		_ = cw.CloseWrite()
+	}
+}

agent_forward_test.go

@@ -1,14 +1,16 @@
 package starssh
 
 import (
+	"bytes"
 	"errors"
 	"io"
+	"net"
+	"sync"
 	"sync/atomic"
 	"testing"
 	"time"
 
 	"golang.org/x/crypto/ssh"
-	sshagent "golang.org/x/crypto/ssh/agent"
 )
 
 type testCloser struct {
@@ -20,15 +22,90 @@ func (c *testCloser) Close() error {
 	return nil
 }
 
+type trackedConn struct {
+	net.Conn
+	closed atomic.Int32
+}
+
+func (c *trackedConn) Close() error {
+	c.closed.Add(1)
+	if c.Conn == nil {
+		return nil
+	}
+	return c.Conn.Close()
+}
+
+type testSSHChannel struct {
+	readFunc func([]byte) (int, error)
+
+	stderr    bytes.Buffer
+	closed    atomic.Int32
+	closeOnce sync.Once
+	closeCh   chan struct{}
+}
+
+func newTestSSHChannel(readFunc func([]byte) (int, error)) *testSSHChannel {
+	return &testSSHChannel{
+		readFunc: readFunc,
+		closeCh:  make(chan struct{}),
+	}
+}
+
+func newBlockingTestSSHChannel() *testSSHChannel {
+	ch := newTestSSHChannel(nil)
+	ch.readFunc = func(p []byte) (int, error) {
+		<-ch.closeCh
+		return 0, io.EOF
+	}
+	return ch
+}
+
+func (c *testSSHChannel) Read(p []byte) (int, error) {
+	if c == nil {
+		return 0, io.EOF
+	}
+	if c.readFunc != nil {
+		return c.readFunc(p)
+	}
+	return 0, io.EOF
+}
+
+func (c *testSSHChannel) Write(p []byte) (int, error) {
+	return len(p), nil
+}
+
+func (c *testSSHChannel) Close() error {
+	if c == nil {
+		return nil
+	}
+	c.closeOnce.Do(func() {
+		c.closed.Add(1)
+		close(c.closeCh)
+	})
+	return nil
+}
+
+func (c *testSSHChannel) CloseWrite() error {
+	return nil
+}
+
+func (c *testSSHChannel) SendRequest(name string, wantReply bool, payload []byte) (bool, error) {
+	return false, nil
+}
+
+func (c *testSSHChannel) Stderr() io.ReadWriter {
+	return &c.stderr
+}
+
 func TestNewExecSessionEnablesAgentForwardingOnce(t *testing.T) {
 	oldNewSSHSession := newSSHSession
-	oldNewSSHAgentForwarder := newSSHAgentForwarder
+	oldProbeSSHAgentForwarding := probeSSHAgentForwarding
 	oldRouteSSHAgentForwarding := routeSSHAgentForwarding
 	oldRequestSSHAgentForwarding := requestSSHAgentForwarding
 	oldCloseSSHClient := closeSSHClient
 	t.Cleanup(func() {
 		newSSHSession = oldNewSSHSession
-		newSSHAgentForwarder = oldNewSSHAgentForwarder
+		probeSSHAgentForwarding = oldProbeSSHAgentForwarding
 		routeSSHAgentForwarding = oldRouteSSHAgentForwarding
 		requestSSHAgentForwarding = oldRequestSSHAgentForwarding
 		closeSSHClient = oldCloseSSHClient
@@ -50,26 +127,26 @@ func TestNewExecSessionEnablesAgentForwardingOnce(t *testing.T) {
 		return &ssh.Session{}, nil
 	}
 
-	var agentInitCalls atomic.Int32
+	var probeCalls atomic.Int32
 	closer := &testCloser{}
-	newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+	probeSSHAgentForwarding = func(timeout time.Duration) error {
-		agentInitCalls.Add(1)
+		probeCalls.Add(1)
 		if timeout != time.Second {
 			t.Fatalf("unexpected forwarding timeout: %v", timeout)
 		}
-		return sshagent.NewKeyring(), closer, nil
+		return nil
 	}
 
 	var routeCalls atomic.Int32
-	routeSSHAgentForwarding = func(client *ssh.Client, keyring sshagent.Agent) error {
+	routeSSHAgentForwarding = func(client *ssh.Client, timeout time.Duration) (io.Closer, error) {
 		routeCalls.Add(1)
 		if client != baseClient {
 			t.Fatalf("unexpected routed client %p", client)
 		}
-		if keyring == nil {
+		if timeout != time.Second {
-			t.Fatal("expected non-nil forwarded agent keyring")
+			t.Fatalf("unexpected routed timeout: %v", timeout)
 		}
-		return nil
+		return closer, nil
 	}
 
 	var requestCalls atomic.Int32
@@ -88,8 +165,8 @@ func TestNewExecSessionEnablesAgentForwardingOnce(t *testing.T) {
 		t.Fatalf("second exec session: %v", err)
 	}
 
-	if agentInitCalls.Load() != 1 {
+	if probeCalls.Load() != 1 {
-		t.Fatalf("expected one agent forwarder init, got %d", agentInitCalls.Load())
+		t.Fatalf("expected one agent probe, got %d", probeCalls.Load())
 	}
 	if routeCalls.Load() != 1 {
 		t.Fatalf("expected one agent route registration, got %d", routeCalls.Load())
@@ -110,13 +187,13 @@ func TestNewExecSessionEnablesAgentForwardingOnce(t *testing.T) {
 func TestNewPTYSessionEnablesAgentForwardingWhenConfigured(t *testing.T) {
 	oldNewSSHSession := newSSHSession
 	oldRequestSessionPTY := requestSessionPTY
-	oldNewSSHAgentForwarder := newSSHAgentForwarder
+	oldProbeSSHAgentForwarding := probeSSHAgentForwarding
 	oldRouteSSHAgentForwarding := routeSSHAgentForwarding
 	oldRequestSSHAgentForwarding := requestSSHAgentForwarding
 	t.Cleanup(func() {
 		newSSHSession = oldNewSSHSession
 		requestSessionPTY = oldRequestSessionPTY
-		newSSHAgentForwarder = oldNewSSHAgentForwarder
+		probeSSHAgentForwarding = oldProbeSSHAgentForwarding
 		routeSSHAgentForwarding = oldRouteSSHAgentForwarding
 		requestSSHAgentForwarding = oldRequestSSHAgentForwarding
 	})
@@ -138,10 +215,12 @@ func TestNewPTYSessionEnablesAgentForwardingWhenConfigured(t *testing.T) {
 		return nil
 	}
 
-	newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+	probeSSHAgentForwarding = func(timeout time.Duration) error {
-		return sshagent.NewKeyring(), &testCloser{}, nil
+		return nil
+	}
+	routeSSHAgentForwarding = func(client *ssh.Client, timeout time.Duration) (io.Closer, error) {
+		return &testCloser{}, nil
 	}
-	routeSSHAgentForwarding = func(client *ssh.Client, keyring sshagent.Agent) error { return nil }
 
 	var requestCalls atomic.Int32
 	requestSSHAgentForwarding = func(session *ssh.Session) error {
@@ -162,11 +241,11 @@ func TestNewPTYSessionEnablesAgentForwardingWhenConfigured(t *testing.T) {
 
 func TestNewExecSessionSkipsAgentForwardingWhenDisabled(t *testing.T) {
 	oldNewSSHSession := newSSHSession
-	oldNewSSHAgentForwarder := newSSHAgentForwarder
+	oldProbeSSHAgentForwarding := probeSSHAgentForwarding
 	oldRequestSSHAgentForwarding := requestSSHAgentForwarding
 	t.Cleanup(func() {
 		newSSHSession = oldNewSSHSession
-		newSSHAgentForwarder = oldNewSSHAgentForwarder
+		probeSSHAgentForwarding = oldProbeSSHAgentForwarding
 		requestSSHAgentForwarding = oldRequestSSHAgentForwarding
 	})
 
@@ -176,9 +255,9 @@ func TestNewExecSessionSkipsAgentForwardingWhenDisabled(t *testing.T) {
 	newSSHSession = func(client *ssh.Client) (*ssh.Session, error) {
 		return &ssh.Session{}, nil
 	}
-	newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+	probeSSHAgentForwarding = func(timeout time.Duration) error {
-		t.Fatal("agent forwarder should not initialize when disabled")
+		t.Fatal("agent forwarding probe should not run when disabled")
-		return nil, nil, nil
+		return nil
 	}
 	requestSSHAgentForwarding = func(session *ssh.Session) error {
 		t.Fatal("agent forwarding should not be requested when disabled")
@@ -191,18 +270,18 @@ func TestNewExecSessionSkipsAgentForwardingWhenDisabled(t *testing.T) {
 }
 
 func TestRequestAgentForwardingReturnsUnavailableError(t *testing.T) {
-	oldNewSSHAgentForwarder := newSSHAgentForwarder
+	oldProbeSSHAgentForwarding := probeSSHAgentForwarding
 	oldRequestSSHAgentForwarding := requestSSHAgentForwarding
 	t.Cleanup(func() {
-		newSSHAgentForwarder = oldNewSSHAgentForwarder
+		probeSSHAgentForwarding = oldProbeSSHAgentForwarding
 		requestSSHAgentForwarding = oldRequestSSHAgentForwarding
 	})
 
 	star := &StarSSH{}
 	star.setTransport(&ssh.Client{}, nil)
 
-	newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+	probeSSHAgentForwarding = func(timeout time.Duration) error {
-		return nil, nil, errors.New("ssh-agent forwarding unavailable: ssh-agent unavailable")
+		return errors.New("ssh-agent forwarding unavailable: ssh-agent unavailable")
 	}
 	requestSSHAgentForwarding = func(session *ssh.Session) error {
 		t.Fatal("session request should not run when agent forwarder init fails")
@@ -216,16 +295,16 @@ func TestRequestAgentForwardingReturnsUnavailableError(t *testing.T) {
 }
 
 func TestRequestAgentForwardingWrapsSetupErrorAsUnavailable(t *testing.T) {
-	oldNewSSHAgentForwarder := newSSHAgentForwarder
+	oldProbeSSHAgentForwarding := probeSSHAgentForwarding
 	t.Cleanup(func() {
-		newSSHAgentForwarder = oldNewSSHAgentForwarder
+		probeSSHAgentForwarding = oldProbeSSHAgentForwarding
 	})
 
 	star := &StarSSH{}
 	star.setTransport(&ssh.Client{}, nil)
 
-	newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+	probeSSHAgentForwarding = func(timeout time.Duration) error {
-		return nil, nil, errors.New("dial unix /tmp/ssh-broken.sock: connect: permission denied")
+		return errors.New("dial unix /tmp/ssh-broken.sock: connect: permission denied")
 	}
 
 	err := star.RequestAgentForwarding(&ssh.Session{})
@@ -235,11 +314,11 @@ func TestRequestAgentForwardingWrapsSetupErrorAsUnavailable(t *testing.T) {
 }
 
 func TestRequestAgentForwardingReturnsDeniedError(t *testing.T) {
-	oldNewSSHAgentForwarder := newSSHAgentForwarder
+	oldProbeSSHAgentForwarding := probeSSHAgentForwarding
 	oldRouteSSHAgentForwarding := routeSSHAgentForwarding
 	oldRequestSSHAgentForwarding := requestSSHAgentForwarding
 	t.Cleanup(func() {
-		newSSHAgentForwarder = oldNewSSHAgentForwarder
+		probeSSHAgentForwarding = oldProbeSSHAgentForwarding
 		routeSSHAgentForwarding = oldRouteSSHAgentForwarding
 		requestSSHAgentForwarding = oldRequestSSHAgentForwarding
 	})
@@ -247,10 +326,12 @@ func TestRequestAgentForwardingReturnsDeniedError(t *testing.T) {
 	star := &StarSSH{}
 	star.setTransport(&ssh.Client{}, nil)
 
-	newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+	probeSSHAgentForwarding = func(timeout time.Duration) error {
-		return sshagent.NewKeyring(), &testCloser{}, nil
+		return nil
+	}
+	routeSSHAgentForwarding = func(client *ssh.Client, timeout time.Duration) (io.Closer, error) {
+		return &testCloser{}, nil
 	}
-	routeSSHAgentForwarding = func(client *ssh.Client, keyring sshagent.Agent) error { return nil }
 	requestSSHAgentForwarding = func(session *ssh.Session) error {
 		return errors.New("forwarding request denied")
 	}
@@ -263,12 +344,12 @@ func TestRequestAgentForwardingReturnsDeniedError(t *testing.T) {
 
 func TestNewExecSessionIgnoresAgentForwardingDenied(t *testing.T) {
 	oldNewSSHSession := newSSHSession
-	oldNewSSHAgentForwarder := newSSHAgentForwarder
+	oldProbeSSHAgentForwarding := probeSSHAgentForwarding
 	oldRouteSSHAgentForwarding := routeSSHAgentForwarding
 	oldRequestSSHAgentForwarding := requestSSHAgentForwarding
 	t.Cleanup(func() {
 		newSSHSession = oldNewSSHSession
-		newSSHAgentForwarder = oldNewSSHAgentForwarder
+		probeSSHAgentForwarding = oldProbeSSHAgentForwarding
 		routeSSHAgentForwarding = oldRouteSSHAgentForwarding
 		requestSSHAgentForwarding = oldRequestSSHAgentForwarding
 	})
@@ -283,10 +364,12 @@ func TestNewExecSessionIgnoresAgentForwardingDenied(t *testing.T) {
 	newSSHSession = func(client *ssh.Client) (*ssh.Session, error) {
 		return &ssh.Session{}, nil
 	}
-	newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+	probeSSHAgentForwarding = func(timeout time.Duration) error {
-		return sshagent.NewKeyring(), &testCloser{}, nil
+		return nil
+	}
+	routeSSHAgentForwarding = func(client *ssh.Client, timeout time.Duration) (io.Closer, error) {
+		return &testCloser{}, nil
 	}
-	routeSSHAgentForwarding = func(client *ssh.Client, keyring sshagent.Agent) error { return nil }
 	requestSSHAgentForwarding = func(session *ssh.Session) error {
 		return errors.New("forwarding request denied")
 	}
@@ -298,10 +381,10 @@ func TestNewExecSessionIgnoresAgentForwardingDenied(t *testing.T) {
 
 func TestNewExecSessionIgnoresAgentForwardingUnavailable(t *testing.T) {
 	oldNewSSHSession := newSSHSession
-	oldNewSSHAgentForwarder := newSSHAgentForwarder
+	oldProbeSSHAgentForwarding := probeSSHAgentForwarding
 	t.Cleanup(func() {
 		newSSHSession = oldNewSSHSession
-		newSSHAgentForwarder = oldNewSSHAgentForwarder
+		probeSSHAgentForwarding = oldProbeSSHAgentForwarding
 	})
 
 	star := &StarSSH{
@@ -314,8 +397,8 @@ func TestNewExecSessionIgnoresAgentForwardingUnavailable(t *testing.T) {
 	newSSHSession = func(client *ssh.Client) (*ssh.Session, error) {
 		return &ssh.Session{}, nil
 	}
-	newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+	probeSSHAgentForwarding = func(timeout time.Duration) error {
-		return nil, nil, errors.New("ssh-agent forwarding unavailable: ssh-agent unavailable")
+		return errors.New("ssh-agent forwarding unavailable: ssh-agent unavailable")
 	}
 
 	if _, err := star.NewExecSession(); err != nil {
@@ -325,10 +408,10 @@ func TestNewExecSessionIgnoresAgentForwardingUnavailable(t *testing.T) {
 
 func TestNewExecSessionIgnoresAgentForwardingSetupError(t *testing.T) {
 	oldNewSSHSession := newSSHSession
-	oldNewSSHAgentForwarder := newSSHAgentForwarder
+	oldProbeSSHAgentForwarding := probeSSHAgentForwarding
 	t.Cleanup(func() {
 		newSSHSession = oldNewSSHSession
-		newSSHAgentForwarder = oldNewSSHAgentForwarder
+		probeSSHAgentForwarding = oldProbeSSHAgentForwarding
 	})
 
 	star := &StarSSH{
@@ -341,8 +424,8 @@ func TestNewExecSessionIgnoresAgentForwardingSetupError(t *testing.T) {
 	newSSHSession = func(client *ssh.Client) (*ssh.Session, error) {
 		return &ssh.Session{}, nil
 	}
-	newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+	probeSSHAgentForwarding = func(timeout time.Duration) error {
-		return nil, nil, errors.New("dial unix /tmp/ssh-broken.sock: connect: connection refused")
+		return errors.New("dial unix /tmp/ssh-broken.sock: connect: connection refused")
 	}
 
 	if _, err := star.NewExecSession(); err != nil {
@@ -351,11 +434,11 @@ func TestNewExecSessionIgnoresAgentForwardingSetupError(t *testing.T) {
 }
 
 func TestEnsureAgentForwardingClosesNewForwarderWhenCloseStarts(t *testing.T) {
-	oldNewSSHAgentForwarder := newSSHAgentForwarder
+	oldProbeSSHAgentForwarding := probeSSHAgentForwarding
 	oldRouteSSHAgentForwarding := routeSSHAgentForwarding
 	oldCloseSSHClient := closeSSHClient
 	t.Cleanup(func() {
-		newSSHAgentForwarder = oldNewSSHAgentForwarder
+		probeSSHAgentForwarding = oldProbeSSHAgentForwarding
 		routeSSHAgentForwarding = oldRouteSSHAgentForwarding
 		closeSSHClient = oldCloseSSHClient
 	})
@@ -370,13 +453,13 @@ func TestEnsureAgentForwardingClosesNewForwarderWhenCloseStarts(t *testing.T) {
 	started := make(chan struct{})
 	release := make(chan struct{})
 	closer := &testCloser{}
-	newSSHAgentForwarder = func(timeout time.Duration) (sshagent.Agent, io.Closer, error) {
+	probeSSHAgentForwarding = func(timeout time.Duration) error {
+		return nil
+	}
+	routeSSHAgentForwarding = func(client *ssh.Client, timeout time.Duration) (io.Closer, error) {
 		close(started)
 		<-release
-		return sshagent.NewKeyring(), closer, nil
+		return closer, nil
-	}
-	routeSSHAgentForwarding = func(client *ssh.Client, keyring sshagent.Agent) error {
-		return nil
 	}
 	closeSSHClient = func(client sshClientRequester) error { return nil }
 
@@ -415,3 +498,75 @@ func TestEnsureAgentForwardingClosesNewForwarderWhenCloseStarts(t *testing.T) {
 		t.Fatal("expected no leaked agent forwarder after close race")
 	}
 }
+
+func TestProxySSHAgentChannelClosesBlockedAgentConnWhenRemoteChannelEnds(t *testing.T) {
+	agentConn, peerConn := net.Pipe()
+	defer peerConn.Close()
+
+	tracked := &trackedConn{Conn: agentConn}
+	channel := newTestSSHChannel(func(p []byte) (int, error) {
+		return 0, io.EOF
+	})
+
+	done := make(chan struct{})
+	go func() {
+		proxySSHAgentChannel(channel, tracked)
+		close(done)
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(time.Second):
+		t.Fatal("proxySSHAgentChannel did not exit after remote EOF")
+	}
+
+	if tracked.closed.Load() == 0 {
+		t.Fatal("expected local agent connection to be closed")
+	}
+	if channel.closed.Load() == 0 {
+		t.Fatal("expected ssh channel to be closed")
+	}
+}
+
+func TestSSHAgentForwardProxyCloseClosesActiveBridges(t *testing.T) {
+	agentConn, peerConn := net.Pipe()
+	defer peerConn.Close()
+
+	tracked := &trackedConn{Conn: agentConn}
+	channel := newBlockingTestSSHChannel()
+	proxy := &sshAgentForwardProxy{
+		stopCh: make(chan struct{}),
+		active: make(map[*sshAgentForwardBridge]struct{}),
+	}
+	bridge := &sshAgentForwardBridge{
+		proxy:   proxy,
+		channel: channel,
+		conn:    tracked,
+	}
+	if !proxy.registerBridge(bridge) {
+		t.Fatal("expected bridge registration to succeed")
+	}
+
+	done := make(chan struct{})
+	go func() {
+		bridge.run()
+		close(done)
+	}()
+
+	if err := proxy.Close(); err != nil {
+		t.Fatalf("close proxy: %v", err)
+	}
+
+	select {
+	case <-done:
+	case <-time.After(time.Second):
+		t.Fatal("bridge did not exit after proxy close")
+	}
+
+	if tracked.closed.Load() == 0 {
+		t.Fatal("expected proxy close to close local agent connection")
+	}
+	if channel.closed.Load() == 0 {
+		t.Fatal("expected proxy close to close ssh channel")
+	}
+}