fix(server): process empty doc embedding (#12417)

fix CLOUD-219

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

## Summary by CodeRabbit

- **Bug Fixes**
  - Ensured that documents without content now receive a placeholder embedding, improving consistency in document processing.

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

packages/backend/server/src/plugins/copilot/context/embedding.ts

@@ -7,7 +7,12 @@ import { chunk } from 'lodash-es';
 
 import { ChunkSimilarity, Embedding } from '../../../models';
 import { OpenAIConfig } from '../providers/openai';
-import { EmbeddingClient, getReRankSchema, ReRankResult } from './types';
+import {
+  EMBEDDING_DIMENSIONS,
+  EmbeddingClient,
+  getReRankSchema,
+  ReRankResult,
+} from './types';
 
 const RERANK_MODEL = 'gpt-4.1-mini';
 
@@ -24,7 +29,7 @@ export class OpenAIEmbeddingClient extends EmbeddingClient {
 
   async getEmbeddings(input: string[]): Promise<Embedding[]> {
     const modelInstance = this.#instance.embedding('text-embedding-3-large', {
-      dimensions: 1024,
+      dimensions: EMBEDDING_DIMENSIONS,
     });
 
     const { embeddings } = await embedMany({
@@ -124,7 +129,9 @@ export class MockEmbeddingClient extends EmbeddingClient {
     return input.map((_, i) => ({
       index: i,
       content: input[i],
-      embedding: Array.from({ length: 1024 }, () => Math.random()),
+      embedding: Array.from({ length: EMBEDDING_DIMENSIONS }, () =>
+        Math.random()
+      ),
     }));
   }
 }

packages/backend/server/src/plugins/copilot/context/job.ts

@@ -16,7 +16,7 @@ import { Models } from '../../../models';
 import { CopilotStorage } from '../storage';
 import { readStream } from '../utils';
 import { OpenAIEmbeddingClient } from './embedding';
-import { EmbeddingClient } from './types';
+import { EMBEDDING_DIMENSIONS, EmbeddingClient } from './types';
 
 @Injectable()
 export class CopilotContextDocJob {
@@ -225,16 +225,29 @@ export class CopilotContextDocJob {
       const content = await this.doc.getFullDocContent(workspaceId, docId);
       if (content) {
         // fast fall for empty doc, journal is easily to create a empty doc
-        if (!content.summary) return;
-        const embeddings = await this.embeddingClient.getFileEmbeddings(
-          new File([content.summary], `${content.title || 'Untitled'}.md`)
-        );
+        if (content.summary) {
+          const embeddings = await this.embeddingClient.getFileEmbeddings(
+            new File([content.summary], `${content.title || 'Untitled'}.md`)
+          );
 
-        for (const chunks of embeddings) {
+          for (const chunks of embeddings) {
+            await this.models.copilotContext.insertWorkspaceEmbedding(
+              workspaceId,
+              docId,
+              chunks
+            );
+          }
+        } else {
+          // for empty doc, insert empty embedding
+          const emptyEmbedding = {
+            index: 0,
+            content: '',
+            embedding: Array.from({ length: EMBEDDING_DIMENSIONS }, () => 0),
+          };
           await this.models.copilotContext.insertWorkspaceEmbedding(
             workspaceId,
             docId,
-            chunks
+            [emptyEmbedding]
           );
         }
       } else if (contextId) {

packages/backend/server/src/plugins/copilot/context/types.ts

@@ -57,6 +57,8 @@ export type Chunk = {
   content: string;
 };
 
+export const EMBEDDING_DIMENSIONS = 1024;
+
 export abstract class EmbeddingClient {
   async getFileEmbeddings(
     file: File,