feat(ai): session persist + continue HTTP/UI, checkpoints, queue

落地 docs/16 P1：会话落盘与真续跑（prior tool 轨迹）、incomplete「加预算继续」、
awaiting_confirm outcome、同参拒+第4/6轮检查点、侧栏忙时单槽排队。
Ask 真 token 流式记缺口（三协议 SSE 成本高）。

server/internal/ai/session.go

@@ -1,33 +1,48 @@
 package ai
 
 import (
+	"crypto/rand"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"os"
 	"path/filepath"
+	"sort"
+	"strings"
 	"time"
 )
 
-// Session 桌面本地会话（目标态落盘；HTTP 路由可后挂）。
+// Session 桌面本地会话（落盘 ~/.opsxdb/ai-sessions/<id>.json）。
 type Session struct {
-	ID        string         `json:"id"`
-	Title     string         `json:"title,omitempty"`
-	Status    string         `json:"status"` // idle|running|incomplete|completed|failed|cancelled
-	CreatedAt string         `json:"createdAt"`
-	UpdatedAt string         `json:"updatedAt"`
-	Messages  []Message      `json:"messages"`
-	Runs      []SessionRun   `json:"runs,omitempty"`
+	ID        string       `json:"id"`
+	Title     string       `json:"title,omitempty"`
+	Status    string       `json:"status"` // idle|running|incomplete|completed|failed|cancelled|awaiting_confirm
+	CreatedAt string       `json:"createdAt"`
+	UpdatedAt string       `json:"updatedAt"`
+	Messages  []Message    `json:"messages"`
+	Runs      []SessionRun `json:"runs,omitempty"`
 }
 
 // SessionRun 一次运行摘要。
 type SessionRun struct {
-	RunID             string `json:"runId"`
-	Outcome           string `json:"outcome"`
-	IncompleteReason  string `json:"incompleteReason,omitempty"`
-	Resumable         bool   `json:"resumable"`
-	StepsUsed         int    `json:"stepsUsed"`
-	StepsBudget       int    `json:"stepsBudget"`
-	FinishedAt        string `json:"finishedAt"`
+	RunID            string `json:"runId"`
+	Outcome          string `json:"outcome"`
+	IncompleteReason string `json:"incompleteReason,omitempty"`
+	Resumable        bool   `json:"resumable"`
+	StepsUsed        int    `json:"stepsUsed"`
+	StepsBudget      int    `json:"stepsBudget"`
+	FinishedAt       string `json:"finishedAt"`
+}
+
+// SessionSummary 列表项（不含 messages）。
+type SessionSummary struct {
+	ID        string `json:"id"`
+	Title     string `json:"title,omitempty"`
+	Status    string `json:"status"`
+	CreatedAt string `json:"createdAt"`
+	UpdatedAt string `json:"updatedAt"`
+	MsgCount  int    `json:"msgCount"`
+	LastRunID string `json:"lastRunId,omitempty"`
 }
 
 func sessionsDir() (string, error) {
@@ -44,9 +59,20 @@ func SessionPath(id string) (string, error) {
 	if err != nil {
 		return "", err
 	}
+	id = strings.TrimSpace(id)
+	if id == "" || strings.ContainsAny(id, `/\`) {
+		return "", fmt.Errorf("invalid session id")
+	}
 	return filepath.Join(dir, id+".json"), nil
 }
 
+// NewSessionID 生成 sess_… 短 id。
+func NewSessionID() string {
+	var b [8]byte
+	_, _ = rand.Read(b[:])
+	return "sess_" + hex.EncodeToString(b[:])
+}
+
 // SaveSession 脱敏后写入磁盘。
 func SaveSession(s Session) error {
 	if s.ID == "" {
@@ -87,3 +113,118 @@ func LoadSession(id string) (Session, error) {
 	}
 	return s, nil
 }
+
+// ListSessions 按 UpdatedAt 倒序；limit<=0 表示全部。
+func ListSessions(limit int) ([]SessionSummary, error) {
+	dir, err := sessionsDir()
+	if err != nil {
+		return nil, err
+	}
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return []SessionSummary{}, nil
+		}
+		return nil, err
+	}
+	var out []SessionSummary
+	for _, e := range entries {
+		if e.IsDir() || !strings.HasSuffix(e.Name(), ".json") {
+			continue
+		}
+		id := strings.TrimSuffix(e.Name(), ".json")
+		s, err := LoadSession(id)
+		if err != nil {
+			continue
+		}
+		sum := SessionSummary{
+			ID: s.ID, Title: s.Title, Status: s.Status,
+			CreatedAt: s.CreatedAt, UpdatedAt: s.UpdatedAt,
+			MsgCount: len(s.Messages),
+		}
+		if n := len(s.Runs); n > 0 {
+			sum.LastRunID = s.Runs[n-1].RunID
+		}
+		out = append(out, sum)
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].UpdatedAt > out[j].UpdatedAt })
+	if limit > 0 && len(out) > limit {
+		out = out[:limit]
+	}
+	return out, nil
+}
+
+// DeleteSession 删除会话文件。
+func DeleteSession(id string) error {
+	path, err := SessionPath(id)
+	if err != nil {
+		return err
+	}
+	err = os.Remove(path)
+	if os.IsNotExist(err) {
+		return nil
+	}
+	return err
+}
+
+// OutcomeToSessionStatus 映射 RunOutcome → Session.Status。
+func OutcomeToSessionStatus(outcome string) string {
+	switch outcome {
+	case OutcomeIncomplete:
+		return "incomplete"
+	case OutcomeAwaitingConfirm:
+		return "awaiting_confirm"
+	case OutcomeFailed:
+		return "failed"
+	case OutcomeCancelled:
+		return "cancelled"
+	case OutcomeCompleted:
+		return "completed"
+	default:
+		if outcome == "" {
+			return "idle"
+		}
+		return outcome
+	}
+}
+
+// PersistAgentRun 把本趟轨迹与 outcome 写入会话（真·续跑用）。
+func PersistAgentRun(sessionID, title string, trajectory []Message, res AgentRes) (Session, error) {
+	sessionID = strings.TrimSpace(sessionID)
+	if sessionID == "" {
+		sessionID = NewSessionID()
+	}
+	s, err := LoadSession(sessionID)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return Session{}, err
+		}
+		s = Session{ID: sessionID, Status: "idle"}
+	}
+	if title != "" && s.Title == "" {
+		// 标题取首条 user 或短截断
+		t := strings.TrimSpace(title)
+		r := []rune(t)
+		if len(r) > 48 {
+			t = string(r[:48]) + "…"
+		}
+		s.Title = t
+	}
+	if len(trajectory) > 0 {
+		s.Messages = trajectory
+	}
+	s.Status = OutcomeToSessionStatus(res.Outcome)
+	s.Runs = append(s.Runs, SessionRun{
+		RunID:            res.RunID,
+		Outcome:          res.Outcome,
+		IncompleteReason: res.IncompleteReason,
+		Resumable:        res.Resumable,
+		StepsUsed:        res.Rounds,
+		StepsBudget:      res.StepsBudget,
+		FinishedAt:       time.Now().Format(time.RFC3339),
+	})
+	if err := SaveSession(s); err != nil {
+		return Session{}, err
+	}
+	return s, nil
+}