fix: improve custom widget AI assistant feedback (#42095)

## Summary

- render Custom Widget AI assistant responses with the existing shared
Ask AI Markdown renderer while keeping user messages as plain text
- expose the existing CE Markdown renderer through the edition-aware GPT
barrel so CE and EE reuse one implementation
- animate the Generating loader icon
- add regression coverage for the assistant/user rendering boundary

## Testing

- CE: 29 Custom Widget AI Assistant tests pass
- CE: ESLint passes with no new errors
- CE: TypeScript check passes
- EE sync simulation: final net patch applies cleanly onto latest
appsmith-ee release
- EE sync simulation: no PR-related TypeScript failures
- git diff validation and CE pre-push edition guard pass

## Linear


https://linear.app/appsmith/issue/APP-15735/replace-internal-appsmith-app-with-native-co-pilot-component

## Automation

/ok-to-test tags="@tag.All"

### 🔍 Cypress test results
<!-- This is an auto-generated comment: Cypress test results  -->
> [!TIP]
> 🟢 🟢 🟢 All cypress tests have passed! 🎉 🎉 🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/31082751527>
> Commit: 61a8087
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=31082751527&attempt=2"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.All`
> Spec:
> <hr>Thu, 06 Aug 2026 09:11:50 UTC
<!-- end of auto-generated comment: Cypress test results  -->

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
  * AI assistant responses now support formatted Markdown rendering.
* User messages continue to display as plain text for clear distinction.
* Added a rotating loading indicator while the assistant is processing.

* **Tests**
* Added coverage confirming Markdown formatting for assistant responses
and plain-text rendering for user messages.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: tomjose92

app/client/src/ce/components/editorComponents/GPT/index.tsx

@@ -11,6 +11,7 @@ import { AISidePanel } from "./AISidePanel";
 
 // Re-export the new components
 export { AISidePanel } from "./AISidePanel";
+export { AIMarkdownRenderer } from "./shared";
 
 export type AIEditorContext = Partial<{
   functionName: string;

app/client/src/pages/Editor/CustomWidgetBuilder/Editor/AIAssistant/index.test.tsx

@@ -30,6 +30,12 @@ jest.mock("ee/utils/AnalyticsUtil", () => ({
   default: { logEvent: jest.fn() },
 }));
 
+jest.mock("ee/components/editorComponents/GPT", () => ({
+  AIMarkdownRenderer: ({ content }: { content: string }) => (
+    <div data-testid="t--custom-widget-ai-markdown">{content}</div>
+  ),
+}));
+
 const mockStore = configureStore();
 
 const SRC_DOC = {
@@ -178,6 +184,26 @@ describe("CustomWidgetBuilder AIAssistant", () => {
     expect(screen.queryByText(/color: red/)).not.toBeInTheDocument();
   });
 
+  it("uses the markdown renderer for assistant responses and keeps user messages plain", () => {
+    renderAssistant({
+      aiAssistant: {
+        messages: [
+          { role: "user", content: "**Keep this literal**", timestamp: 1 },
+          {
+            role: "assistant",
+            content: "## Features\n\n**Inline editing**",
+            timestamp: 2,
+          },
+        ],
+      },
+    });
+
+    expect(
+      screen.getByTestId("t--custom-widget-ai-markdown"),
+    ).toHaveTextContent("## Features **Inline editing**");
+    expect(screen.getByText("**Keep this literal**")).toBeInTheDocument();
+  });
+
   it("does not re-apply older assistant messages", () => {
     const bulkUpdate = jest.fn();
 

app/client/src/pages/Editor/CustomWidgetBuilder/Editor/AIAssistant/index.tsx

@@ -20,6 +20,7 @@ import {
   Text,
   Tooltip,
 } from "@appsmith/ads";
+import { AIMarkdownRenderer } from "ee/components/editorComponents/GPT";
 import type { ContentProps } from "pages/Editor/CustomWidgetBuilder/Editor/CodeEditors/types";
 import { CustomWidgetBuilderContext } from "pages/Editor/CustomWidgetBuilder";
 import {
@@ -95,6 +96,19 @@ const fadeIn = keyframes`
   }
 `;
 
+const rotate = keyframes`
+  from {
+    transform: rotate(0deg);
+  }
+  to {
+    transform: rotate(360deg);
+  }
+`;
+
+const LoadingIcon = styled(Icon)`
+  animation: ${rotate} 1s linear infinite;
+`;
+
 const EmptyState = styled.div`
   display: flex;
   flex-direction: column;
@@ -565,7 +579,11 @@ export function AIAssistant(props: ContentProps) {
                 ? createMessage(CUSTOM_WIDGET_AI_ASSISTANT.USER_LABEL)
                 : createMessage(CUSTOM_WIDGET_AI_ASSISTANT.ASSISTANT_LABEL)}
             </MessageHeader>
-            <UserMessageContent>{message.content}</UserMessageContent>
+            {message.role === "user" ? (
+              <UserMessageContent>{message.content}</UserMessageContent>
+            ) : (
+              <AIMarkdownRenderer content={message.content} />
+            )}
             {message.appliedFiles.length > 0 && (
               <AppliedUpdates>
                 <Text color="var(--ads-v2-color-fg-muted)" kind="body-s">
@@ -589,7 +607,7 @@ export function AIAssistant(props: ContentProps) {
         {isLoading && (
           <LoadingState>
             <LoadingText>
-              <Icon name="loader-line" size="sm" />
+              <LoadingIcon name="loader-line" size="sm" />
               {createMessage(CUSTOM_WIDGET_AI_ASSISTANT.THINKING)}
             </LoadingText>
           </LoadingState>