feat(agent-chat): 修复智能体会话归属与历史路由恢复：侧边栏按当前agent过滤会话并携带agent上下文跳转，补充旧线程路径回溯到智能体工作区，防止误入通用问答，并完善输入框记忆按钮显隐与侧边栏展开入口，提升体验一致性。

frontend-web/src/core/threads/utils.ts

@@ -27,6 +27,18 @@ function pickAgentRef(
   return undefined;
 }
 
+/**
+ * Return the agent that owns a thread when that ownership was persisted on
+ * either its run context or its metadata.  Keeping this in one place ensures
+ * sidebars and route recovery make the same decision for older deep links.
+ */
+export function agentRefOfThread(thread: {
+  context?: ThreadAgentRef | null;
+  metadata?: Record<string, unknown> | null;
+}): string | undefined {
+  return pickAgentRef(thread.context, thread.metadata);
+}
+
 export function pathOfThread(
   thread: ThreadRouteTarget,
   context?: ThreadAgentRef | null,
@@ -36,7 +48,7 @@ export function pathOfThread(
   const agentRef =
     typeof thread === "string"
       ? pickAgentRef(context, null)
-      : pickAgentRef(thread.context, thread.metadata);
+      : agentRefOfThread(thread) ?? pickAgentRef(context, null);
 
   return agentRef
     ? `${base}/agents/${encodeURIComponent(agentRef)}/chats/${threadId}`