fix: ai chat block added later should be with higher index (#7660)

[BS-1000](https://linear.app/affine-design/issue/BS-1000/更好地处理新增内容的层级)

packages/frontend/core/src/blocksuite/presets/ai/_common/chat-actions-handle.ts

@@ -131,7 +131,7 @@ function getViewportCenter(
 
 // Add AI chat block and focus on it
 function addAIChatBlock(
-  doc: Doc,
+  host: EditorHost,
   messages: ChatMessage[],
   sessionId: string,
   viewportCenter: { x: number; y: number }
@@ -140,6 +140,7 @@ function addAIChatBlock(
     return;
   }
 
+  const { doc } = host;
   const surfaceBlock = doc
     .getBlocks()
     .find(block => block.flavour === 'affine:surface');
@@ -147,6 +148,8 @@ function addAIChatBlock(
     return;
   }
 
+  const surfaceService = host.spec.getService('affine:surface');
+  const { layer } = surfaceService;
   // Add AI chat block to the center of the viewport
   const width = 300; // AI_CHAT_BLOCK_WIDTH = 300
   const height = 320; // AI_CHAT_BLOCK_HEIGHT = 320
@@ -158,6 +161,7 @@ function addAIChatBlock(
     {
       xywh: bound.serialize(),
       messages: JSON.stringify(messages),
+      index: layer.generateIndex('affine:embed-ai-chat'),
       sessionId,
     },
     surfaceBlock.id
@@ -329,7 +333,7 @@ const SAVE_CHAT_TO_BLOCK_ACTION: ChatAction = {
 
       // After switching to edgeless mode, the user can save the chat to a block
       const blockId = addAIChatBlock(
-        host.doc,
+        host,
         messages,
         newSessionId,
         viewportCenter

packages/frontend/core/src/blocksuite/presets/ai/peek-view/chat-block-peek-view.ts

@@ -180,7 +180,8 @@ export class AIChatBlockPeekView extends LitElement {
       return;
     }
 
-    const aiChatBlockId = doc.addBlock(
+    const edgelessService = this._rootService as EdgelessRootService;
+    const aiChatBlockId = edgelessService.addBlock(
       'affine:embed-ai-chat' as keyof BlockSuite.BlockModels,
       {
         xywh: bound.serialize(),
@@ -197,7 +198,6 @@ export class AIChatBlockPeekView extends LitElement {
     this.updateContext({ currentChatBlockId: aiChatBlockId });
 
     // Connect the parent chat block to the AI chat block
-    const edgelessService = this._rootService as EdgelessRootService;
     edgelessService.addElement(CanvasElementType.CONNECTOR, {
       mode: ConnectorMode.Curve,
       controllers: [],