feat(agent): Agent 工作台 - 计划插话记忆、统一模型选择器并修复摘要与视频入库

将计划清单、运行中插话和个人记忆接入云端 Agent；全站模型选择器统一为左右二级菜单。画布摘要按预算截断不再整轮拒绝，首页视频未知宽高可入库。README 补充贡献者 morrow。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/app/cloud_agent_stuck.go

@@ -0,0 +1,80 @@
+package app
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"time"
+
+	"infinite-canvas/backend/internal/model"
+	"infinite-canvas/backend/internal/repository"
+)
+
+const cloudAgentStuckAfter = 5 * time.Minute
+const cloudAgentConflictLogThreshold = 15
+
+func (s *Service) terminateStuckCloudAgent(run *model.CloudAgentExecution) bool {
+	if run == nil || run.CleanupPending || (run.Status != "running" && run.Status != "queued") {
+		return false
+	}
+	state, err := cloudAgentDecode(run)
+	if err != nil {
+		return false
+	}
+	if s.cloudAgentHasLiveWork(run, &state) {
+		return false
+	}
+	last := cloudAgentLastEventAt(&state)
+	if last.IsZero() || time.Since(last) < cloudAgentStuckAfter {
+		return false
+	}
+	idle := time.Since(last)
+	if err := s.terminateCloudAgent(run, fmt.Sprintf("运行已 %.0f 分钟没有任何进展（既没有新事件、也没有在跑的任务），已判定为卡住并停止；可以重新发起", idle.Minutes())); err != nil {
+		if !errors.Is(err, repository.ErrCreationConflict) {
+			log.Printf("agent stuck cleanup %s: %v", run.ID, err)
+		}
+		return false
+	}
+	log.Printf("agent scheduler: run=%s 判定卡死并收尾（最后一条事件在 %.0f 分钟前）", run.ID, idle.Minutes())
+	return true
+}
+
+func (s *Service) cloudAgentHasLiveWork(run *model.CloudAgentExecution, state *cloudAgentRuntime) bool {
+	for _, taskID := range []string{state.ActiveTaskID, state.MediaTaskID, state.StoryboardTaskID} {
+		if taskID == "" {
+			continue
+		}
+		task, err := s.repo.TaskForUser(run.UserID, taskID)
+		if err != nil {
+			return true
+		}
+		if task.Status == model.TaskStatusQueued || task.Status == model.TaskStatusRunning {
+			return true
+		}
+	}
+	return false
+}
+
+func cloudAgentLastEventAt(state *cloudAgentRuntime) time.Time {
+	if state == nil || len(state.Events) == 0 {
+		return time.Time{}
+	}
+	return state.Events[len(state.Events)-1].CreatedAt
+}
+
+func (s *Service) noteCloudAgentSchedulerConflict(runID string) {
+	if s.agentConflictStreak == nil {
+		s.agentConflictStreak = map[string]int{}
+	}
+	s.agentConflictStreak[runID]++
+	if streak := s.agentConflictStreak[runID]; streak == cloudAgentConflictLogThreshold {
+		log.Printf("agent scheduler: run=%s 连续 %d 次 CAS 冲突（另有写者持续占用该行），这一轮很可能卡住了", runID, streak)
+	}
+}
+
+func (s *Service) clearCloudAgentSchedulerConflict(runID string) {
+	if s.agentConflictStreak == nil {
+		return
+	}
+	delete(s.agentConflictStreak, runID)
+}