fix(core): pasted code artifact should be inserted as codeblock (#13492)

fix AI-417

#### PR Dependency Tree


* **PR #13492** 👈

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**
* Copying code snippets now uses a rich format for improved paste
fidelity in compatible editors.
* Preserves code block formatting and language when pasted, reducing
manual cleanup.
* Continues to support plain text and HTML paste for broad
compatibility.
  * Works more reliably when moving content within the app.
  * Existing copy confirmation remains unchanged.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/core/src/blocksuite/ai/components/ai-tools/code-artifact.ts

@@ -3,6 +3,11 @@ import { SignalWatcher, WithDisposable } from '@blocksuite/affine/global/lit';
 import { ColorScheme } from '@blocksuite/affine/model';
 import { unsafeCSSVar, unsafeCSSVarV2 } from '@blocksuite/affine/shared/theme';
 import { type BlockStdScope } from '@blocksuite/affine/std';
+import {
+  type BlockSnapshot,
+  nanoid,
+  type SliceSnapshot,
+} from '@blocksuite/affine/store';
 import type { NotificationService } from '@blocksuite/affine-shared/services';
 import {
   CodeBlockIcon,
@@ -496,6 +501,10 @@ export class CodeArtifactTool extends ArtifactTool<
     </div>`;
   }
 
+  get clipboard() {
+    return this.std?.clipboard;
+  }
+
   protected override getPreviewControls() {
     if (this.data.type !== 'tool-result' || !this.std || !this.data.result) {
       return undefined;
@@ -506,7 +515,39 @@ export class CodeArtifactTool extends ArtifactTool<
     const title = result.title;
 
     const copyHTML = async () => {
-      await navigator.clipboard.writeText(htmlContent).catch(console.error);
+      const codeBlock: BlockSnapshot = {
+        type: 'block',
+        id: nanoid(),
+        flavour: 'affine:code',
+        version: 1,
+        props: {
+          language: 'html',
+          wrap: false,
+          caption: '',
+          text: {
+            '$blocksuite:internal:text$': true,
+            delta: [{ insert: htmlContent }],
+          },
+        },
+        children: [],
+      };
+
+      const sliceSnapshot: SliceSnapshot = {
+        type: 'slice',
+        content: [codeBlock],
+        workspaceId: 'fake-workspace-id',
+        pageId: 'fake-page-id',
+      };
+
+      await this.clipboard?.writeToClipboard(items => ({
+        ...items,
+        'text/plain': htmlContent,
+        'text/html': htmlContent,
+        'BLOCKSUITE/SNAPSHOT': JSON.stringify({
+          snapshot: sliceSnapshot,
+          blobs: {},
+        }),
+      }));
       this.notificationService.toast('Copied HTML to clipboard');
     };