fix(control-ui): prevent chat tab freeze when loading long history

- Request at most 25 messages from chat.history (was 200) to reduce payload
  size and JSON parse cost in the browser.
- Cap rendered chat history at 25 messages to avoid main-thread freeze
  from rendering many markdown messages (fixes 'tab unresponsive').
- Defer applying messages with requestAnimationFrame so the UI can paint
  'Loading chat...' before the heavy render.
- Cap sessions.list to 40 when loading the chat tab to avoid large
  session dropdown response.

Helps address #10622 (Webchat UI freezes when loading sessions with
many messages). Gateway already caps payload size (#18505); this adds
client-side limits so the Control UI stays responsive with long
sessions.

Made-with: Cursor

ui/src/ui/app-chat.ts

@@ -356,8 +356,8 @@ export async function refreshChat(host: ChatHost, opts?: { scheduleScroll?: bool
   await Promise.all([
     loadChatHistory(host as unknown as OpenClawApp),
     loadSessions(host as unknown as OpenClawApp, {
-      activeMinutes: 0,
-      limit: 0,
+      activeMinutes: CHAT_SESSIONS_ACTIVE_MINUTES,
+      limit: 40,
       includeGlobal: true,
       includeUnknown: true,
     }),

ui/src/ui/controllers/chat.ts

@@ -71,21 +71,27 @@ export async function loadChatHistory(state: ChatState) {
   state.chatLoading = true;
   state.lastError = null;
   try {
+    // Request a small batch to avoid huge payloads and main-thread freeze when
+    // parsing JSON and rendering many markdown messages (browser "tab unresponsive").
+    const CHAT_HISTORY_REQUEST_LIMIT = 25;
     const res = await state.client.request<{ messages?: Array<unknown>; thinkingLevel?: string }>(
       "chat.history",
       {
         sessionKey: state.sessionKey,
-        limit: 200,
+        limit: CHAT_HISTORY_REQUEST_LIMIT,
       },
     );
     const messages = Array.isArray(res.messages) ? res.messages : [];
-    state.chatMessages = messages.filter((message) => !isAssistantSilentReply(message));
+    const filtered = messages.filter((message) => !isAssistantSilentReply(message));
     state.chatThinkingLevel = res.thinkingLevel ?? null;
-    // Clear all streaming state — history includes tool results and text
-    // inline, so keeping streaming artifacts would cause duplicates.
     maybeResetToolStream(state);
     state.chatStream = null;
     state.chatStreamStartedAt = null;
+    // Defer applying messages so the UI can paint "Loading chat..." before the heavy render.
+    state.chatLoading = false;
+    requestAnimationFrame(() => {
+      state.chatMessages = filtered;
+    });
   } catch (err) {
     state.lastError = String(err);
   } finally {

ui/src/ui/views/chat.ts

@@ -1328,7 +1328,8 @@ export function renderChat(props: ChatProps) {
   `;
 }
 
-const CHAT_HISTORY_RENDER_LIMIT = 200;
+// Cap rendered history to avoid main-thread freeze (markdown + DOM for each message).
+const CHAT_HISTORY_RENDER_LIMIT = 25;
 
 function groupMessages(items: ChatItem[]): Array<ChatItem | MessageGroup> {
   const result: Array<ChatItem | MessageGroup> = [];