perf(ai): lazy-load agent chat runtime so it doesn't fetch/diff threads until opened (#21331)

## Problem

On workspaces with a sizeable AI chat history, the whole app was
freezing during navigation, including Settings (one navigation click
measured ~6.5s).

## Root cause

`AgentChatProvider` is mounted app-wide in `AppRouterProviders`, so its
effects run on every page.
On every render it would:
1. auto-select the most recently active thread
(`AgentChatThreadInitializationEffect`),
2. fetch that thread's **full message history**
(`AgentChatMessagesFetchEffect`),
3. run `AgentChatStreamingPartsDiffSyncEffect` →
`updateStreamingPartsWithDiff`, which loops over every message doing
`isDeeplyEqual(existing, incoming)` + `structuredClone`.

A large thread would produce multi-second freeze on every interaction,
app-wide. (Confirmed via a Chrome CPU profile)

 ## Fix

Don't run the agent-chat **message runtime** until the chat is actually
opened.

## Note
There is still room for improvement, opening AI chats would still be
very slow.

packages/twenty-front/src/modules/ai/components/AgentChatProviderContent.tsx

@@ -1,9 +1,4 @@
-import { AgentChatStreamSubscriptionEffect } from '@/ai/components/AgentChatStreamSubscriptionEffect';
-import { AgentChatMessagesFetchEffect } from '@/ai/components/AgentChatMessagesFetchEffect';
-import { AgentChatSessionStartTimeEffect } from '@/ai/components/AgentChatSessionStartTimeEffect';
-
-import { AgentChatStreamingAutoScrollEffect } from '@/ai/components/AgentChatStreamingAutoScrollEffect';
-import { AgentChatStreamingPartsDiffSyncEffect } from '@/ai/components/AgentChatStreamingPartsDiffSyncEffect';
+import { AgentChatRuntimeEffects } from '@/ai/components/AgentChatRuntimeEffects';
 import { AgentChatThreadInitializationEffect } from '@/ai/components/AgentChatThreadInitializationEffect';
 import { AgentChatComponentInstanceContext } from '@/ai/contexts/AgentChatComponentInstanceContext';
 import { Suspense } from 'react';
@@ -19,11 +14,7 @@ export const AgentChatProviderContent = ({
         value={{ instanceId: 'agentChatComponentInstance' }}
       >
         <AgentChatThreadInitializationEffect />
-        <AgentChatMessagesFetchEffect />
-        <AgentChatStreamSubscriptionEffect />
-        <AgentChatStreamingPartsDiffSyncEffect />
-        <AgentChatSessionStartTimeEffect />
-        <AgentChatStreamingAutoScrollEffect />
+        <AgentChatRuntimeEffects />
         {children}
       </AgentChatComponentInstanceContext.Provider>
     </Suspense>

packages/twenty-front/src/modules/ai/components/AgentChatRuntimeEffects.tsx

@@ -0,0 +1,48 @@
+import { AgentChatMessagesFetchEffect } from '@/ai/components/AgentChatMessagesFetchEffect';
+import { AgentChatSessionStartTimeEffect } from '@/ai/components/AgentChatSessionStartTimeEffect';
+import { AgentChatStreamSubscriptionEffect } from '@/ai/components/AgentChatStreamSubscriptionEffect';
+import { AgentChatStreamingAutoScrollEffect } from '@/ai/components/AgentChatStreamingAutoScrollEffect';
+import { AgentChatStreamingPartsDiffSyncEffect } from '@/ai/components/AgentChatStreamingPartsDiffSyncEffect';
+import { hasAgentChatBeenOpenedState } from '@/ai/states/hasAgentChatBeenOpenedState';
+import { isSidePanelOpenedState } from '@/side-panel/states/isSidePanelOpenedState';
+import { sidePanelPageState } from '@/side-panel/states/sidePanelPageState';
+import { useAtomState } from '@/ui/utilities/state/jotai/hooks/useAtomState';
+import { useAtomStateValue } from '@/ui/utilities/state/jotai/hooks/useAtomStateValue';
+import { useEffect } from 'react';
+import { SidePanelPages } from 'twenty-shared/types';
+
+export const AgentChatRuntimeEffects = () => {
+  const isSidePanelOpened = useAtomStateValue(isSidePanelOpenedState);
+  const sidePanelPage = useAtomStateValue(sidePanelPageState);
+
+  const [hasAgentChatBeenOpened, setHasAgentChatBeenOpened] = useAtomState(
+    hasAgentChatBeenOpenedState,
+  );
+
+  const isAgentChatOpen =
+    isSidePanelOpened && sidePanelPage === SidePanelPages.AskAI;
+
+  useEffect(() => {
+    if (isAgentChatOpen && !hasAgentChatBeenOpened) {
+      setHasAgentChatBeenOpened(true);
+    }
+  }, [isAgentChatOpen, hasAgentChatBeenOpened, setHasAgentChatBeenOpened]);
+
+  if (!hasAgentChatBeenOpened) {
+    return null;
+  }
+
+  return (
+    <>
+      <AgentChatMessagesFetchEffect />
+      <AgentChatStreamSubscriptionEffect />
+      <AgentChatSessionStartTimeEffect />
+      {isAgentChatOpen && (
+        <>
+          <AgentChatStreamingPartsDiffSyncEffect />
+          <AgentChatStreamingAutoScrollEffect />
+        </>
+      )}
+    </>
+  );
+};

packages/twenty-front/src/modules/ai/states/hasAgentChatBeenOpenedState.ts

@@ -0,0 +1,6 @@
+import { createAtomState } from '@/ui/utilities/state/jotai/utils/createAtomState';
+
+export const hasAgentChatBeenOpenedState = createAtomState<boolean>({
+  key: 'ai/hasAgentChatBeenOpenedState',
+  defaultValue: false,
+});