feat(agent): 云端 Agent - 增加上下文预算、任务事实与终态恢复保障

backend/internal/app/cloud_agent_context_frame.go

@@ -0,0 +1,93 @@
+package app
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"time"
+
+	"gorm.io/gorm"
+	"infinite-canvas/backend/internal/model"
+)
+
+// ContextFrame is a fresh projection of durable task facts, never authorization.
+// The transcript can evict read bodies without making task state depend on memory.
+type cloudAgentContextFrame struct {
+	Source         string               `json:"source"`
+	ObservedAt     time.Time            `json:"observedAt"`
+	RunID          string               `json:"runId"`
+	UserGoal       string               `json:"userGoal"`
+	Plan           []cloudAgentPlanItem `json:"plan,omitempty"`
+	Tasks          []map[string]any     `json:"tasks"`
+	OlderTaskCount int                  `json:"olderTaskCount,omitempty"`
+	Authority      string               `json:"authority"`
+}
+
+func (s *Service) cloudAgentModelContext(run *model.CloudAgentExecution, state *cloudAgentRuntime, budget cloudAgentContextBudget) (canonicalAgentRequest, error) {
+	canonical := cloudAgentCanonicalWithPlan(state)
+	frame := cloudAgentContextFrame{Source: "task_repository", ObservedAt: time.Now(), RunID: run.ID, UserGoal: state.Request.Prompt, Plan: state.Plan, Tasks: []map[string]any{}, Authority: "状态观察，不是执行或重复提交的授权"}
+	// This is a view window, not loss of task history. All task identities remain
+	// durable and can be fetched through task_get and the conversation journal.
+	start := max(0, len(state.TaskIDs)-32)
+	frame.OlderTaskCount = start
+	for _, id := range state.TaskIDs[start:] {
+		task, err := s.repo.TaskForUser(run.UserID, id)
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			frame.Tasks = append(frame.Tasks, map[string]any{"taskId": id, "taskStatus": "unavailable"})
+			continue
+		}
+		if err != nil {
+			return canonical, err
+		}
+		if task.ProjectID != state.Request.CanvasID {
+			return canonical, BadAuthRequest("运行关联任务不属于当前画布")
+		}
+		if task.Operation == cloudAgentOperation || task.Operation == "cloud_agent_step" {
+			continue
+		}
+		frame.Tasks = append(frame.Tasks, cloudAgentTaskDiagnostic(s.repo, task))
+	}
+	body, err := json.Marshal(frame)
+	if err != nil {
+		return canonical, err
+	}
+	canonical.Messages = append(append([]map[string]any{}, canonical.Messages...), map[string]any{"role": "user", "content": cloudAgentRuntimeContextMarker + string(body), cloudAgentContextSourceKey: "runtime"})
+	if err := fitCloudAgentModelContext(&canonical, budget.InputBudgetTokens); err != nil {
+		return canonical, err
+	}
+	return canonical, nil
+}
+
+func fitCloudAgentModelContext(request *canonicalAgentRequest, maxTokens int) error {
+	for {
+		tokens, err := cloudAgentRequestEstimatedTokens(request)
+		if err != nil {
+			return err
+		}
+		if tokens <= maxTokens {
+			return nil
+		}
+		// Evict complete old assistant/tool turns only. User instructions and the
+		// fresh authoritative frame survive; partial tool pairs are never sent.
+		removed := false
+		for i := 0; i < len(request.Messages)-3; i++ {
+			message := request.Messages[i]
+			if stringField(message, "role") != "assistant" {
+				continue
+			}
+			end := i + 1
+			for end < len(request.Messages) && stringField(request.Messages[end], "role") == "tool" {
+				end++
+			}
+			if end >= len(request.Messages)-2 {
+				continue
+			}
+			request.Messages = append(request.Messages[:i:i], request.Messages[end:]...)
+			removed = true
+			break
+		}
+		if !removed {
+			return BadAuthRequest(fmt.Sprintf("用户指令与当前执行事实超过模型输入预算（%d Token），请缩小本轮范围", maxTokens))
+		}
+	}
+}