fix: 拆分 starssh 的拨号超时与认证超时语义

- 为 LoginInput 新增 DialTimeout，明确区分【TCP/proxy/ssh-agent 拨号超时】和【SSH 握手/认证超时】
- 将 Timeout 收口为握手/认证阶段超时，0 表示不限制，不再在登录入口自动回填默认值
- 新增 effectiveLoginTimeout/effectiveDialTimeout，统一超时决策逻辑
- 调整 login 流程，仅对 login context、ssh.ClientConfig 和握手阶段连接 deadline 使用认证超时
- 调整 transport 拨号链路，默认 TCP dial、proxy dial 与 ssh-agent 建连统一改用 DialTimeout
- 修正 agent forwarding 初始化仍错误复用 LoginInfo.Timeout 的问题
- 保持 LoginSimple 的直观行为：传入 timeout 时同时映射到 Timeout 和 DialTimeout
- 新增 login_timeout_test，覆盖零值不回填、DialTimeout 优先级，以及 ssh-agent 认证路径使用拨号超时的回归测试

login.go

@@ -16,6 +16,7 @@ import (
 
 var ErrHostKeyCallbackRequired = errors.New("host key callback is required; use DefaultAllowHostKeyCallback to explicitly allow any host key")
 var errSSHAgentUnavailable = errors.New("ssh-agent unavailable")
+var buildSSHAgentAuthMethodFunc = buildSSHAgentAuthMethod
 
 var defaultAuthOrder = []AuthMethodKind{
 	AuthMethodSSHAgent,
@@ -42,7 +43,8 @@ func loginWithContext(ctx context.Context, info LoginInput) (*StarSSH, error) {
 		return nil, ErrHostKeyCallbackRequired
 	}
 
-	loginCtx, cancel := contextWithLoginTimeout(ctx, info.Timeout)
+	authTimeout := effectiveLoginTimeout(info)
+	loginCtx, cancel := contextWithLoginTimeout(ctx, authTimeout)
 	defer cancel()
 
 	sshInfo := &StarSSH{
@@ -76,7 +78,7 @@ func loginWithContext(ctx context.Context, info LoginInput) (*StarSSH, error) {
 	clientConfig := &ssh.ClientConfig{
 		User:            info.User,
 		Auth:            auth,
-		Timeout:         info.Timeout,
+		Timeout:         authTimeout,
 		HostKeyCallback: hostKeyCallback,
 		BannerCallback:  bannerCallback,
 	}
@@ -93,7 +95,7 @@ func loginWithContext(ctx context.Context, info LoginInput) (*StarSSH, error) {
 	if err != nil {
 		return sshInfo, err
 	}
-	restoreDeadline := applyConnDeadline(rawConn, loginCtx, info.Timeout)
+	restoreDeadline := applyConnDeadline(rawConn, loginCtx, authTimeout)
 	defer restoreDeadline()
 
 	clientConn, chans, reqs, err := ssh.NewClientConn(rawConn, targetAddr, clientConfig)
@@ -130,6 +132,7 @@ func LoginSimple(host string, user string, passwd string, prikeyPath string, por
 		Addr:            host,
 		Port:            port,
 		Timeout:         timeout,
+		DialTimeout:     timeout,
 		User:            user,
 		HostKeyCallback: DefaultAllowHostKeyCallback,
 	}
@@ -154,12 +157,29 @@ func normalizeLoginInput(info LoginInput) LoginInput {
 	if info.Port <= 0 {
 		info.Port = defaultSSHPort
 	}
-	if info.Timeout <= 0 {
-		info.Timeout = defaultLoginTimeout
-	}
 	return info
 }
 
+func effectiveLoginTimeout(info LoginInput) time.Duration {
+	if info.Timeout <= 0 {
+		return 0
+	}
+	return info.Timeout
+}
+
+func effectiveDialTimeout(info LoginInput) time.Duration {
+	switch {
+	case info.DialTimeout < 0:
+		return 0
+	case info.DialTimeout > 0:
+		return info.DialTimeout
+	case info.Timeout > 0:
+		return info.Timeout
+	default:
+		return defaultLoginTimeout
+	}
+}
+
 func buildAuthMethods(info LoginInput) ([]ssh.AuthMethod, func(), error) {
 	order, err := normalizeAuthOrder(info.AuthOrder)
 	if err != nil {
@@ -194,7 +214,7 @@ func buildAuthMethods(info LoginInput) ([]ssh.AuthMethod, func(), error) {
 			if info.DisableSSHAgent {
 				continue
 			}
-			agentMethod, cleanup, err := buildSSHAgentAuthMethod(info.Timeout)
+			agentMethod, cleanup, err := buildSSHAgentAuthMethodFunc(effectiveDialTimeout(info))
 			if err != nil {
 				agentErr = err
 				continue