fix(agent): Agent 运行 - 重复读取改为软收敛并保留可纠正的媒体失败原因

重复只读和同版本识图不再把运行标成失败，下一步暂时收起只读工具。媒体能力错误改为可纠正，准入失败保留安全原因。

backend/internal/app/cloud_agent_context_frame.go

@@ -27,6 +27,9 @@ var errCloudAgentContextOverBudget = errors.New("Agent model context exceeds inp
 
 func (s *Service) cloudAgentModelContext(run *model.CloudAgentExecution, state *cloudAgentRuntime, budget cloudAgentContextBudget) (canonicalAgentRequest, error) {
 	canonical := cloudAgentCanonicalWithPlan(state)
+	if state.ReadLoopNudge {
+		cloudAgentApplyReadLoopNudge(&canonical, 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.