improvement(chat): code-split resource preview panel out of initial /chat bundle

.claude/rules/sim-imports.md

@@ -31,6 +31,20 @@ import { Dashboard, Sidebar } from '@/app/workspace/[workspaceId]/logs/component
 import { Dashboard } from '@/app/workspace/[workspaceId]/logs/components/dashboard/dashboard'
 ```
 
+## Code-splitting through barrels
+
+When you `lazy(() => import(...))` a component to keep it out of a route's initial bundle, import the **deep module path** (`./components/foo/foo`), never the barrel — and **delete the now-dead barrel re-export** of that component. This app has no `"sideEffects": false` in `apps/sim/package.json`, so when any sibling still imports that barrel, webpack can conservatively keep the barrel's re-export edge to the heavy module. A leftover `export { Foo } from './foo'` line can therefore drag `Foo` (and its transitive deps) back into the initial chunk and silently defeat the split. Removing the dead re-export is the guaranteed fix; verify with a production bundle diff, not by eyeballing the `lazy()` call.
+
+```typescript
+// ✓ Good — deep lazy import + no barrel edge left behind
+const MothershipView = lazy(() =>
+  import('./components/mothership-view/mothership-view').then((m) => ({ default: m.MothershipView }))
+)
+// (and remove `export { MothershipView } from './mothership-view'` from components/index.ts)
+```
+
+Wrap the lazy component in a **local `<Suspense>`** so its suspension resolves at the nearest boundary instead of bubbling to the page-level fallback (which would flash the whole route). `React.lazy(memo(forwardRef(...)))` forwards a DOM `ref` correctly in React 19 — but during the fallback window `ref.current` is `null`, so every consumer must guard it (`if (!el) return` / `el?.`).
+
 ## No Re-exports
 
 Do not re-export from non-barrel files. Import directly from the source.

apps/sim/app/workspace/[workspaceId]/home/components/index.ts

@@ -11,7 +11,6 @@ export {
   MothershipResourcesProvider,
   useMothershipResources,
 } from './mothership-resources-context'
-export { MothershipView } from './mothership-view'
 export { QueuedMessages } from './queued-messages'
 export { SuggestedActions } from './suggested-actions'
 export { UserInput, type UserInputHandle } from './user-input'

apps/sim/app/workspace/[workspaceId]/home/components/user-input/components/prompt-editor/prompt-editor.tsx

@@ -122,6 +122,11 @@ export function PromptEditor({
       return <span>{displayText}</span>
     }
 
+    const contextByLabel = new Map<string, (typeof contexts)[number]>()
+    for (const c of contexts) {
+      if (!contextByLabel.has(c.label)) contextByLabel.set(c.label, c)
+    }
+
     const elements: React.ReactNode[] = []
     let lastIndex = 0
     for (let i = 0; i < ranges.length; i++) {
@@ -133,7 +138,7 @@ export function PromptEditor({
       }
 
       const mentionLabel = stripMentionTrigger(range.token)
-      const matchingCtx = contexts.find((c) => c.label === mentionLabel)
+      const matchingCtx = contextByLabel.get(mentionLabel)
 
       const mentionIconNode = matchingCtx ? (
         <ContextMentionIcon

apps/sim/app/workspace/[workspaceId]/home/home.tsx

@@ -2,7 +2,9 @@
 
 import {
   type Dispatch,
+  lazy,
   type SetStateAction,
+  Suspense,
   useCallback,
   useEffect,
   useMemo,
@@ -49,7 +51,6 @@ import {
   CreditsChip,
   MothershipChat,
   MothershipResourcesProvider,
-  MothershipView,
   SuggestedActions,
   UserInput,
   type UserInputHandle,
@@ -59,6 +60,17 @@ import type { FileAttachmentForApi, MothershipResource, MothershipResourceType }
 
 const logger = createLogger('Home')
 
+/**
+ * The resource preview panel pulls in the file-viewer stack (rich-markdown
+ * editor, CSV/PDF viewers). It only renders once a chat has messages, so it is
+ * code-split out of the initial `/chat` bundle and loaded on demand.
+ */
+const MothershipView = lazy(() =>
+  import('./components/mothership-view/mothership-view').then((m) => ({
+    default: m.MothershipView,
+  }))
+)
+
 interface HomeProps {
   chatId?: string
   userName?: string
@@ -491,18 +503,20 @@ export function Home({ chatId, userName, userId }: HomeProps) {
         reorderResources={reorderResources}
         collapseResource={collapseResource}
       >
-        <MothershipView
-          ref={mothershipRef}
-          workspaceId={workspaceId}
-          chatId={resolvedChatId}
-          resources={resources}
-          activeResourceId={activeResourceId}
-          isCollapsed={isResourceCollapsed}
-          previewSession={previewSession}
-          isAgentResponding={isSending}
-          genericResourceData={genericResourceData ?? undefined}
-          className={skipResourceTransition ? '!transition-none' : undefined}
-        />
+        <Suspense fallback={null}>
+          <MothershipView
+            ref={mothershipRef}
+            workspaceId={workspaceId}
+            chatId={resolvedChatId}
+            resources={resources}
+            activeResourceId={activeResourceId}
+            isCollapsed={isResourceCollapsed}
+            previewSession={previewSession}
+            isAgentResponding={isSending}
+            genericResourceData={genericResourceData ?? undefined}
+            className={skipResourceTransition ? '!transition-none' : undefined}
+          />
+        </Suspense>
       </MothershipResourcesProvider>
 
       {isResourceCollapsed && (