feat: Agent CLI 与终端审计回放全面优化

- Agent CLI: 多轮对话、SSH 长连接、流式推理、Evolver 按用户隔离、历史侧栏
- 终端审计: 回放播放器、命令书签、筛选分页导出、命令输出统计、录制落盘修复
- 修复 session_commands 表迁移、Kill 竞态导致录制丢失、无录制会话回放提示
- 审计历史页只读（移除删除），移除回放弹框录制搜索

backend/pkg/remoteexec/persistent_client.go

@@ -0,0 +1,144 @@
+// persistent_client.go - 任务级 SSH 长连接，多次 Exec 复用同一 client // Logan.Li
+package remoteexec
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"sync"
+	"time"
+
+	"golang.org/x/crypto/ssh"
+)
+
+// PersistentClient 可复用的 SSH 长连接（任务生命周期内持有，Close 释放） // Logan.Li
+type PersistentClient struct {
+	cfg    SSHConfig
+	client *ssh.Client
+	mu     sync.Mutex
+}
+
+// NewPersistentClient 建立 SSH 长连接 // Logan.Li
+func NewPersistentClient(cfg SSHConfig) (*PersistentClient, error) {
+	client, err := connect(cfg)
+	if err != nil {
+		return nil, err
+	}
+	return &PersistentClient{cfg: cfg, client: client}, nil
+}
+
+// Exec 在长连接上执行命令；连接断开时自动重连一次 // Logan.Li
+func (p *PersistentClient) Exec(command string, timeout time.Duration) (*ExecResult, error) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	result, err := p.execLocked(command, timeout)
+	if err == nil {
+		return result, nil
+	}
+	// 连接级失败：重连后重试一次 // Logan.Li
+	if p.client != nil {
+		_ = p.client.Close()
+		p.client = nil
+	}
+	client, connErr := connect(p.cfg)
+	if connErr != nil {
+		return result, err
+	}
+	p.client = client
+	return p.execLocked(command, timeout)
+}
+
+// execLocked 假定已持锁，在当前 client 上执行 // Logan.Li
+func (p *PersistentClient) execLocked(command string, timeout time.Duration) (*ExecResult, error) {
+	if p.client == nil {
+		client, err := connect(p.cfg)
+		if err != nil {
+			return nil, err
+		}
+		p.client = client
+	}
+	return execWithClient(p.client, p.cfg, command, timeout)
+}
+
+// Close 关闭长连接 // Logan.Li
+func (p *PersistentClient) Close() error {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	if p.client == nil {
+		return nil
+	}
+	err := p.client.Close()
+	p.client = nil
+	return err
+}
+
+// execWithClient 在已有 SSH client 上执行命令（供 Exec / PersistentClient 共用） // Logan.Li
+func execWithClient(client *ssh.Client, cfg SSHConfig, command string, timeout time.Duration) (*ExecResult, error) {
+	start := time.Now()
+	result := &ExecResult{Host: cfg.Host, Port: cfg.Port}
+
+	session, err := client.NewSession()
+	if err != nil {
+		result.Duration = time.Since(start).Milliseconds()
+		result.Error = fmt.Sprintf("创建SSH会话失败: %v", err)
+		return result, err
+	}
+	defer session.Close()
+
+	if timeout <= 0 {
+		timeout = 60 * time.Second
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	type execOut struct {
+		output []byte
+		err    error
+	}
+	ch := make(chan execOut, 1)
+
+	go func() {
+		var stdout, stderr bytes.Buffer
+		session.Stdout = &stdout
+		session.Stderr = &stderr
+		runErr := session.Run(command)
+
+		output := stdout.Bytes()
+		if stderr.Len() > 0 {
+			if len(output) > 0 {
+				output = append(output, '\n')
+			}
+			output = append(output, stderr.Bytes()...)
+		}
+		ch <- execOut{output: output, err: runErr}
+	}()
+
+	select {
+	case <-ctx.Done():
+		result.Duration = time.Since(start).Milliseconds()
+		result.Error = fmt.Sprintf("执行超时（%v）", timeout)
+		result.ExitCode = -1
+		return result, fmt.Errorf("exec timeout after %v", timeout)
+	case out := <-ch:
+		result.Duration = time.Since(start).Milliseconds()
+		result.Output = string(out.output)
+
+		if out.err != nil {
+			if exitErr, ok := out.err.(*ssh.ExitError); ok {
+				result.ExitCode = exitErr.ExitStatus()
+				result.Success = false
+			} else {
+				result.ExitCode = -1
+				result.Error = out.err.Error()
+				result.Success = false
+				return result, out.err
+			}
+		} else {
+			result.ExitCode = 0
+			result.Success = true
+		}
+	}
+	return result, nil
+}