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/agent.go

@@ -59,6 +59,8 @@ type AgentRes struct {
 	IncompleteReason string      `json:"incompleteReason,omitempty"`
 	Resumable        bool        `json:"resumable,omitempty"`
 	StepsBudget      int         `json:"stepsBudget,omitempty"`
+	// Trajectory 含 system/user/assistant.tool_calls/tool 的完整对话（供落盘续跑；JSON 默认省略大字段可选）
+	Trajectory       []Message   `json:"trajectory,omitempty"`
 }
 
 // RunAgent 多轮：LLM tool_call → aitools.Runtime.Call → 回灌。
@@ -90,6 +92,11 @@ func runAgent(ctx context.Context, llm ToolChat, rt *aitools.Runtime, req AgentR
 	if runID == "" {
 		runID = NewRunID()
 	}
+	sessionID := strings.TrimSpace(req.SessionID)
+	if sessionID == "" {
+		sessionID = NewSessionID()
+		req.SessionID = sessionID
+	}
 	rt.RunID = runID
 	// Agent 路径禁止模型自行带确认令牌
 	rt.RejectCallerConfirm = true
@@ -119,13 +126,14 @@ func runAgent(ctx context.Context, llm ToolChat, rt *aitools.Runtime, req AgentR
 		}
 	}
 
-	baseMeta := func(steps []AgentStep, rounds int) AgentRes {
+	finish := func(steps []AgentStep, rounds int, msgs []Message) AgentRes {
 		return AgentRes{
 			Steps:       steps,
 			Rounds:      rounds,
 			RunID:       runID,
-			SessionID:   req.SessionID,
+			SessionID:   sessionID,
 			StepsBudget: maxRounds,
+			Trajectory:  append([]Message{}, msgs...),
 		}
 	}
 
@@ -134,19 +142,22 @@ func runAgent(ctx context.Context, llm ToolChat, rt *aitools.Runtime, req AgentR
 	rounds := 0
 	for round := 0; round < maxRounds; round++ {
 		if err := ctx.Err(); err != nil {
-			res := baseMeta(steps, rounds)
+			res := finish(steps, rounds, msgs)
 			res.Content = "已取消"
 			res.Outcome = OutcomeCancelled
 			res.Resumable = len(steps) > 0
-			emitEvent(emit, AgentEvent{Type: AgentEventError, Error: "cancelled", Steps: steps, Rounds: rounds, RunID: runID, Outcome: OutcomeCancelled})
+			emitEvent(emit, AgentEvent{Type: AgentEventError, Error: "cancelled", Steps: steps, Rounds: rounds, RunID: runID, SessionID: sessionID, Outcome: OutcomeCancelled})
 			return res, err
 		}
 		rounds = round + 1
+		if tip := CheckpointHint(rounds); tip != "" {
+			msgs = append(msgs, Message{Role: "system", Content: tip})
+		}
 		turn, err := llm.ChatWithTools(ctx, req.Model, msgs, tools)
 		if err != nil {
-			res := baseMeta(steps, rounds)
+			res := finish(steps, rounds, msgs)
 			res.Outcome = OutcomeFailed
-			emitEvent(emit, AgentEvent{Type: AgentEventError, Error: err.Error(), Steps: steps, Rounds: rounds, RunID: runID, Outcome: OutcomeFailed})
+			emitEvent(emit, AgentEvent{Type: AgentEventError, Error: err.Error(), Steps: steps, Rounds: rounds, RunID: runID, SessionID: sessionID, Outcome: OutcomeFailed})
 			return res, err
 		}
 		if len(turn.ToolCalls) == 0 {
@@ -157,13 +168,13 @@ func runAgent(ctx context.Context, llm ToolChat, rt *aitools.Runtime, req AgentR
 			for _, part := range chunkDelta(content, 36) {
 				emitEvent(emit, AgentEvent{Type: AgentEventDelta, Delta: part})
 			}
-			res := baseMeta(steps, rounds)
+			res := finish(steps, rounds, msgs)
 			res.Content = content
 			res.SQL = extractSQL(content)
 			res.Outcome = OutcomeCompleted
 			emitEvent(emit, AgentEvent{
 				Type: AgentEventDone, Content: res.Content, SQL: res.SQL, Steps: steps, Rounds: rounds,
-				RunID: runID, Outcome: OutcomeCompleted, StepsBudget: maxRounds,
+				RunID: runID, SessionID: sessionID, Outcome: OutcomeCompleted, StepsBudget: maxRounds,
 			})
 			return res, nil
 		}
@@ -217,13 +228,13 @@ func runAgent(ctx context.Context, llm ToolChat, rt *aitools.Runtime, req AgentR
 		}
 		if awaiting {
 			content := "需要确认写操作后才能继续。"
-			res := baseMeta(steps, rounds)
+			res := finish(steps, rounds, msgs)
 			res.Content = content
 			res.Outcome = OutcomeAwaitingConfirm
 			res.Resumable = true
 			emitEvent(emit, AgentEvent{
 				Type: AgentEventDone, Content: content, Steps: steps, Rounds: rounds,
-				RunID: runID, Outcome: OutcomeAwaitingConfirm, Resumable: true, StepsBudget: maxRounds,
+				RunID: runID, SessionID: sessionID, Outcome: OutcomeAwaitingConfirm, Resumable: true, StepsBudget: maxRounds,
 			})
 			return res, nil
 		}
@@ -234,14 +245,14 @@ func runAgent(ctx context.Context, llm ToolChat, rt *aitools.Runtime, req AgentR
 	for _, part := range chunkDelta(content, 36) {
 		emitEvent(emit, AgentEvent{Type: AgentEventDelta, Delta: part})
 	}
-	res := baseMeta(steps, rounds)
+	res := finish(steps, rounds, msgs)
 	res.Content = content
 	res.Outcome = OutcomeIncomplete
 	res.IncompleteReason = ReasonMaxSteps
 	res.Resumable = true
 	emitEvent(emit, AgentEvent{
 		Type: AgentEventIncomplete, Content: content, Steps: steps, Rounds: rounds,
-		RunID: runID, Outcome: OutcomeIncomplete, IncompleteReason: ReasonMaxSteps,
+		RunID: runID, SessionID: sessionID, Outcome: OutcomeIncomplete, IncompleteReason: ReasonMaxSteps,
 		Resumable: true, StepsBudget: maxRounds,
 	})
 	return res, nil