feat(core): support compose a doc tool (#13013)

#### PR Dependency Tree


* **PR #13013** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

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

* **New Features**
* Introduced a document composition tool for AI chat, allowing users to
generate, preview, and save structured markdown documents directly from
chat interactions.
* Added an artifact preview panel for enhanced document previews within
the chat interface.
* Enabled dynamic content rendering in the chat panel's right section
for richer user experiences.

* **Improvements**
  * Sidebar maximum width increased for greater workspace flexibility.
* Enhanced chat message and split view styling for improved layout and
usability.

* **Bug Fixes**
  * None.

* **Other**
* Registered new custom elements for AI tools and artifact preview
functionality.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/copilot/providers/utils.ts

@@ -11,6 +11,7 @@ import {
 import { ZodType } from 'zod';
 
 import {
+  createDocComposeTool,
   createDocEditTool,
   createDocKeywordSearchTool,
   createDocReadTool,
@@ -388,6 +389,7 @@ export interface CustomAITools extends ToolSet {
   doc_semantic_search: ReturnType<typeof createDocSemanticSearchTool>;
   doc_keyword_search: ReturnType<typeof createDocKeywordSearchTool>;
   doc_read: ReturnType<typeof createDocReadTool>;
+  doc_compose: ReturnType<typeof createDocComposeTool>;
   web_search_exa: ReturnType<typeof createExaSearchTool>;
   web_crawl_exa: ReturnType<typeof createExaCrawlTool>;
 }
@@ -457,6 +459,10 @@ export class TextStreamParser {
             result += `\nReading the doc "${chunk.args.doc_id}"\n`;
             break;
           }
+          case 'doc_compose': {
+            result += `\nWriting document "${chunk.args.title}"\n`;
+            break;
+          }
         }
         result = this.markAsCallout(result);
         break;
@@ -486,6 +492,16 @@ export class TextStreamParser {
             }
             break;
           }
+          case 'doc_compose': {
+            if (
+              chunk.result &&
+              typeof chunk.result === 'object' &&
+              'title' in chunk.result
+            ) {
+              result += `\nDocument "${chunk.result.title}" created successfully with ${chunk.result.wordCount} words.\n`;
+            }
+            break;
+          }
           case 'web_search_exa': {
             if (Array.isArray(chunk.result)) {
               result += `\n${this.getWebSearchLinks(chunk.result)}\n`;