修复多会话任务栏抖动、会话跳回与停止失效 (#264)

* fix(web): stabilize active task ordering

* fix(chat): preserve navigation during conversation startup

* fix(tasks): guarantee hard cancellation

* fix(chat): bind navigation and hard stop targets

* fix(chat): prevent replay from reclaiming navigation

internal/handler/task_manager.go

@@ -3,6 +3,7 @@ package handler
 import (
 	"context"
 	"errors"
+	"sort"
 	"strings"
 	"sync"
 	"time"
@@ -484,7 +485,10 @@ func (m *AgentTaskManager) CancelTask(conversationID string, cause error) (bool,
 	if runtimeCancel != nil {
 		runtimeHandled = runtimeCancel(cause)
 	}
-	if cancel != nil && !runtimeHandled {
+	// 「彻底停止」必须同时取消宿主 context：原生 Agent Cancel 即使已受理，
+	// 也可能只在安全点返回或报告超时，不能据此让整条任务继续存活。
+	// 中断并继续仍保留原语义：原生取消已处理时由运行时负责恢复。
+	if cancel != nil && (!runtimeHandled || errors.Is(cause, ErrTaskCancelled)) {
 		cancel(cause)
 	}
 	if toolCanceler != nil {
@@ -591,6 +595,12 @@ func (m *AgentTaskManager) GetActiveTasks() []*AgentTask {
 			Status:         task.Status,
 		})
 	}
+	sort.Slice(result, func(i, j int) bool {
+		if result[i].StartedAt.Equal(result[j].StartedAt) {
+			return result[i].ConversationID < result[j].ConversationID
+		}
+		return result[i].StartedAt.Before(result[j].StartedAt)
+	})
 	return result
 }