diff --git a/webui/src/App.tsx b/webui/src/App.tsx
index fabcff180..591cf4a96 100644
--- a/webui/src/App.tsx
+++ b/webui/src/App.tsx
@@ -17,6 +17,7 @@ import {
   loadSavedSecret,
   saveSecret,
 } from "@/lib/bootstrap";
+import { deriveTitle } from "@/lib/format";
 import { NanobotClient } from "@/lib/nanobot-client";
 import { ClientProvider, useClient } from "@/providers/ClientProvider";
 import type { ChatSummary } from "@/lib/types";
@@ -391,8 +392,7 @@ function Shell({
 
   const headerTitle = activeSession
     ? activeSession.title ||
-      activeSession.preview ||
-      t("chat.fallbackTitle", { id: activeSession.chatId.slice(0, 6) })
+      deriveTitle(activeSession.preview, t("chat.newChat"))
     : t("app.brand");
 
   useEffect(() => {
diff --git a/webui/src/components/ChatList.tsx b/webui/src/components/ChatList.tsx
index fc667883c..a51076519 100644
--- a/webui/src/components/ChatList.tsx
+++ b/webui/src/components/ChatList.tsx
@@ -7,6 +7,7 @@ import {
   DropdownMenuItem,
   DropdownMenuTrigger,
 } from "@/components/ui/dropdown-menu";
+import { deriveTitle } from "@/lib/format";
 import { cn } from "@/lib/utils";
 import type { ChatSummary } from "@/lib/types";
 
@@ -64,8 +65,11 @@ export function ChatList({
                 const fallbackTitle = t("chat.fallbackTitle", {
                   id: s.chatId.slice(0, 6),
                 });
-                const rawLabel = (s.title || s.preview)?.trim();
-                const title = rawLabel || fallbackTitle;
+                const generatedTitle = s.title?.trim() || "";
+                const title =
+                  generatedTitle || deriveTitle(s.preview, t("chat.newChat"));
+                const tooltipTitle =
+                  generatedTitle || deriveTitle(s.preview, fallbackTitle);
                 return (
                   <li key={s.key} className="min-w-0">
                     <div
@@ -79,7 +83,7 @@ export function ChatList({
                       <button
                         type="button"
                         onClick={() => onSelect(s.key)}
-                        title={rawLabel || fallbackTitle}
+                        title={tooltipTitle}
                         className="min-w-0 flex-1 overflow-hidden py-1.5 text-left"
                       >
                         <span className="block w-full truncate font-medium leading-5">{title}</span>
diff --git a/webui/src/components/ConnectionBadge.tsx b/webui/src/components/ConnectionBadge.tsx
index 7616ddbe5..a09aadd28 100644
--- a/webui/src/components/ConnectionBadge.tsx
+++ b/webui/src/components/ConnectionBadge.tsx
@@ -36,21 +36,25 @@ export function ConnectionBadge() {
     status === "connecting" ||
     status === "reconnecting" ||
     status === "error";
+  const label = t(`connection.${status}`);
   return (
     <span
       className={cn(
-        "inline-flex min-w-0 items-center gap-1.5 rounded-md px-1.5 py-1 text-[11px] font-medium transition-colors",
+        "inline-flex h-8 w-8 shrink-0 items-center justify-center rounded-full transition-colors",
+        "text-muted-foreground/70 hover:bg-sidebar-accent/65",
         meta.color,
       )}
       aria-live="polite"
+      role="status"
+      title={label}
     >
-      <span className="relative flex h-1.5 w-1.5" aria-hidden>
+      <span className="relative flex h-2 w-2" aria-hidden>
         {pulsing && (
           <span className="absolute inline-flex h-full w-full animate-ping rounded-full bg-current opacity-75" />
         )}
-        <span className="relative inline-flex h-1.5 w-1.5 rounded-full bg-current" />
+        <span className="relative inline-flex h-2 w-2 rounded-full bg-current" />
       </span>
-      {t(`connection.${status}`)}
+      <span className="sr-only">{label}</span>
     </span>
   );
 }
diff --git a/webui/src/components/Sidebar.tsx b/webui/src/components/Sidebar.tsx
index cf21c8865..cd55475fe 100644
--- a/webui/src/components/Sidebar.tsx
+++ b/webui/src/components/Sidebar.tsx
@@ -117,12 +117,12 @@ export function Sidebar(props: SidebarProps) {
         />
       </div>
       <Separator className="bg-sidebar-border/50" />
-      <div className="space-y-1 px-2.5 py-2.5 text-xs">
+      <div className="flex items-center gap-1 px-2.5 py-2.5 text-xs">
         <Button
           type="button"
           variant="ghost"
           onClick={props.onOpenSettings}
-          className="h-8 w-full justify-start gap-2 rounded-full px-2.5 text-[12.5px] font-medium text-sidebar-foreground/85 hover:bg-sidebar-accent/75 hover:text-sidebar-foreground"
+          className="h-8 min-w-0 flex-1 justify-start gap-2 rounded-full px-2.5 text-[12.5px] font-medium text-sidebar-foreground/85 hover:bg-sidebar-accent/75 hover:text-sidebar-foreground"
         >
           <Settings className="h-3.5 w-3.5" aria-hidden />
           {t("sidebar.settings")}
diff --git a/webui/src/components/thread/ThreadShell.tsx b/webui/src/components/thread/ThreadShell.tsx
index a4844d304..5711b6ce1 100644
--- a/webui/src/components/thread/ThreadShell.tsx
+++ b/webui/src/components/thread/ThreadShell.tsx
@@ -167,8 +167,9 @@ export function ThreadShell({
 
   useEffect(() => {
     if (!chatId) return;
-    return client.onSessionUpdate((updatedChatId) => {
+    return client.onSessionUpdate((updatedChatId, scope) => {
       if (updatedChatId !== chatId) return;
+      if (scope === "metadata") return;
       pendingCanonicalHydrateRef.current.add(chatId);
       refreshHistory();
     });
diff --git a/webui/src/lib/format.ts b/webui/src/lib/format.ts
index 1c2600119..b5a3722f6 100644
--- a/webui/src/lib/format.ts
+++ b/webui/src/lib/format.ts
@@ -1,10 +1,35 @@
 import i18n, { currentLocale } from "@/i18n";
 
+const LOW_INFORMATION_TITLE_PREVIEWS = new Set([
+  "hi",
+  "hello",
+  "hey",
+  "hello nano",
+  "hello nanobot",
+  "hi nano",
+  "hi nanobot",
+  "你好",
+  "您好",
+  "嗨",
+  "哈喽",
+  "哈啰",
+  "在吗",
+]);
+
+function isLowInformationTitlePreview(text: string): boolean {
+  const normalized = text.toLowerCase().replace(/[.!?。！？~～\s]+$/g, "").trim();
+  return (
+    normalized.startsWith("/") ||
+    LOW_INFORMATION_TITLE_PREVIEWS.has(normalized)
+  );
+}
+
 /** Truncate the first user message into a chat title. */
 export function deriveTitle(preview: string | undefined, fallback: string): string {
   if (!preview) return fallback;
   const oneLine = preview.replace(/\s+/g, " ").trim();
   if (!oneLine) return fallback;
+  if (isLowInformationTitlePreview(oneLine)) return fallback;
   return oneLine.length > 60 ? `${oneLine.slice(0, 57)}…` : oneLine;
 }
 
diff --git a/webui/src/lib/nanobot-client.ts b/webui/src/lib/nanobot-client.ts
index ded368741..dfddf688a 100644
--- a/webui/src/lib/nanobot-client.ts
+++ b/webui/src/lib/nanobot-client.ts
@@ -54,7 +54,8 @@ type Unsubscribe = () => void;
 type EventHandler = (ev: InboundEvent) => void;
 type StatusHandler = (status: ConnectionStatus) => void;
 type RuntimeModelHandler = (modelName: string | null, modelPreset?: string | null) => void;
-type SessionUpdateHandler = (chatId: string) => void;
+type SessionUpdateScope = "metadata" | "thread" | string;
+type SessionUpdateHandler = (chatId: string, scope?: SessionUpdateScope) => void;
 
 /** Structured connection-level errors surfaced to the UI.
  *
@@ -364,7 +365,7 @@ export class NanobotClient {
     }
 
     if (parsed.event === "session_updated") {
-      this.emitSessionUpdate(parsed.chat_id);
+      this.emitSessionUpdate(parsed.chat_id, parsed.scope);
       return;
     }
 
@@ -382,9 +383,9 @@ export class NanobotClient {
     }
   }
 
-  private emitSessionUpdate(chatId: string): void {
+  private emitSessionUpdate(chatId: string, scope?: SessionUpdateScope): void {
     for (const handler of this.sessionUpdateHandlers) {
-      handler(chatId);
+      handler(chatId, scope);
     }
   }
 
diff --git a/webui/src/tests/nanobot-client.test.ts b/webui/src/tests/nanobot-client.test.ts
index f5ac3f45e..6b434bb34 100644
--- a/webui/src/tests/nanobot-client.test.ts
+++ b/webui/src/tests/nanobot-client.test.ts
@@ -233,9 +233,13 @@ describe("NanobotClient", () => {
     client.connect();
     lastSocket().fakeOpen();
 
-    lastSocket().fakeMessage({ event: "session_updated", chat_id: "chat-title" });
+    lastSocket().fakeMessage({
+      event: "session_updated",
+      chat_id: "chat-title",
+      scope: "metadata",
+    });
 
-    expect(globalHandler).toHaveBeenCalledWith("chat-title");
+    expect(globalHandler).toHaveBeenCalledWith("chat-title", "metadata");
     expect(chatHandler).not.toHaveBeenCalled();
   });
 
diff --git a/webui/src/tests/thread-shell.test.tsx b/webui/src/tests/thread-shell.test.tsx
index c768b5a42..9e8a59f2d 100644
--- a/webui/src/tests/thread-shell.test.tsx
+++ b/webui/src/tests/thread-shell.test.tsx
@@ -8,7 +8,7 @@ import type { UIMessage } from "@/lib/types";
 function makeClient() {
   const errorHandlers = new Set<(err: { kind: string }) => void>();
   const chatHandlers = new Map<string, Set<(ev: import("@/lib/types").InboundEvent) => void>>();
-  const sessionUpdateHandlers = new Set<(chatId: string) => void>();
+  const sessionUpdateHandlers = new Set<(chatId: string, scope?: string) => void>();
   const goalStateByChatId = new Map<string, import("@/lib/types").GoalStateWsPayload>();
   return {
     status: "open" as const,
@@ -34,7 +34,7 @@ function makeClient() {
         errorHandlers.delete(handler);
       };
     },
-    onSessionUpdate: (handler: (chatId: string) => void) => {
+    onSessionUpdate: (handler: (chatId: string, scope?: string) => void) => {
       sessionUpdateHandlers.add(handler);
       return () => {
         sessionUpdateHandlers.delete(handler);
@@ -49,8 +49,8 @@ function makeClient() {
       }
       for (const h of chatHandlers.get(chatId) ?? []) h(ev);
     },
-    _emitSessionUpdate(chatId: string) {
-      for (const h of sessionUpdateHandlers) h(chatId);
+    _emitSessionUpdate(chatId: string, scope?: string) {
+      for (const h of sessionUpdateHandlers) h(chatId, scope);
     },
     sendMessage: vi.fn(),
     newChat: vi.fn(),
@@ -651,6 +651,52 @@ describe("ThreadShell", () => {
     expect(historyCalls).toBe(1);
   });
 
+  it("does not refetch thread history for metadata-only session updates", async () => {
+    const client = makeClient();
+    let historyCalls = 0;
+    vi.stubGlobal(
+      "fetch",
+      vi.fn(async (input: RequestInfo | URL) => {
+        const url = String(input);
+        if (url.includes("websocket%3Achat-a/webui-thread")) {
+          historyCalls += 1;
+          return httpJson(
+            transcriptFromSimpleMessages([
+              { role: "user", content: "question" },
+              { role: "assistant", content: "answer" },
+            ]),
+          );
+        }
+        return {
+          ok: false,
+          status: 404,
+          json: async () => ({}),
+        };
+      }),
+    );
+
+    render(
+      wrap(
+        client,
+        <ThreadShell
+          session={session("chat-a")}
+          title="Chat chat-a"
+          onToggleSidebar={() => {}}
+          onNewChat={() => {}}
+        />,
+      ),
+    );
+
+    await waitFor(() => expect(screen.getByText("answer")).toBeInTheDocument());
+    expect(historyCalls).toBe(1);
+
+    await act(async () => {
+      client._emitSessionUpdate("chat-a", "metadata");
+    });
+
+    expect(historyCalls).toBe(1);
+  });
+
   it("scrolls to the bottom after loading a session from the blank new-chat page", async () => {
     const client = makeClient();
     const scrollIntoView = vi.fn();
diff --git a/webui/src/tests/useSessions.test.tsx b/webui/src/tests/useSessions.test.tsx
index 9e340a66a..72df813e0 100644
--- a/webui/src/tests/useSessions.test.tsx
+++ b/webui/src/tests/useSessions.test.tsx
@@ -2,7 +2,7 @@ import { act, renderHook, waitFor } from "@testing-library/react";
 import type { ReactNode } from "react";
 import { beforeEach, describe, expect, it, vi } from "vitest";
 
-import { useSessionHistory, useSessions } from "@/hooks/useSessions";
+import { sessionTitle, useSessionHistory, useSessions } from "@/hooks/useSessions";
 import * as api from "@/lib/api";
 import { ClientProvider } from "@/providers/ClientProvider";
 
@@ -17,7 +17,7 @@ vi.mock("@/lib/api", async (importOriginal) => {
 });
 
 function fakeClient() {
-  const sessionUpdateHandlers = new Set<(chatId: string) => void>();
+  const sessionUpdateHandlers = new Set<(chatId: string, scope?: string) => void>();
   return {
     status: "open" as const,
     defaultChatId: null as string | null,
@@ -25,12 +25,12 @@ function fakeClient() {
     onError: () => () => {},
     onChat: () => () => {},
     getRunStartedAt: () => null,
-    onSessionUpdate: (handler: (chatId: string) => void) => {
+    onSessionUpdate: (handler: (chatId: string, scope?: string) => void) => {
       sessionUpdateHandlers.add(handler);
       return () => sessionUpdateHandlers.delete(handler);
     },
-    emitSessionUpdate: (chatId: string) => {
-      for (const handler of sessionUpdateHandlers) handler(chatId);
+    emitSessionUpdate: (chatId: string, scope?: string) => {
+      for (const handler of sessionUpdateHandlers) handler(chatId, scope);
     },
     sendMessage: vi.fn(),
     newChat: vi.fn(),
@@ -61,6 +61,28 @@ describe("useSessions", () => {
     vi.mocked(api.fetchWebuiThread).mockReset();
   });
 
+  it("does not use low-information greetings as fallback session titles", () => {
+    expect(sessionTitle({
+      key: "websocket:chat-hi",
+      channel: "websocket",
+      chatId: "chat-hi",
+      createdAt: "2026-04-16T10:00:00Z",
+      updatedAt: "2026-04-16T10:00:00Z",
+      title: "",
+      preview: "hi",
+    })).toBe("New chat");
+
+    expect(sessionTitle({
+      key: "websocket:chat-work",
+      channel: "websocket",
+      chatId: "chat-work",
+      createdAt: "2026-04-16T10:00:00Z",
+      updatedAt: "2026-04-16T10:00:00Z",
+      title: "",
+      preview: "帮我优化 WebUI 性能",
+    })).toBe("帮我优化 WebUI 性能");
+  });
+
   it("removes a session from the local list after delete succeeds", async () => {
     vi.mocked(api.listSessions).mockResolvedValue([
       {