feat(server): faster reranking based on confidence (#12957)

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

## Summary by CodeRabbit

* **New Features**
* Improved document reranking with a more streamlined and accurate
scoring system.
* Enhanced support for binary ("yes"/"no") document relevance judgments.

* **Improvements**
* Simplified user prompts and output formats for reranking tasks, making
results easier to interpret.
  * Increased reliability and consistency in document ranking results.

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

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

@@ -17,7 +17,6 @@ import {
 import {
   EMBEDDING_DIMENSIONS,
   EmbeddingClient,
-  getReRankSchema,
   type ReRankResult,
 } from './types';
 
@@ -81,9 +80,9 @@ class ProductionEmbeddingClient extends EmbeddingClient {
   }
 
   private getTargetId<T extends ChunkSimilarity>(embedding: T) {
-    return 'docId' in embedding
+    return 'docId' in embedding && typeof embedding.docId === 'string'
       ? embedding.docId
-      : 'fileId' in embedding
+      : 'fileId' in embedding && typeof embedding.fileId === 'string'
         ? embedding.fileId
         : '';
   }
@@ -102,24 +101,19 @@ class ProductionEmbeddingClient extends EmbeddingClient {
       throw new CopilotPromptNotFound({ name: RERANK_PROMPT });
     }
     const provider = await this.getProvider({ modelId: prompt.model });
-    const schema = getReRankSchema(embeddings.length);
 
-    const ranks = await provider.structure(
+    const ranks = await provider.rerank(
       { modelId: prompt.model },
-      prompt.finish({
-        query,
-        results: embeddings.map(e => ({
-          targetId: this.getTargetId(e),
-          chunk: e.chunk,
-          content: e.content,
-        })),
-        schema,
-      }),
-      { maxRetries: 3, signal }
+      embeddings.map(e => prompt.finish({ query, doc: e.content })),
+      { signal }
     );
 
     try {
-      return schema.parse(JSON.parse(ranks)).ranks;
+      return ranks.map((score, i) => ({
+        chunk: embeddings[i].content,
+        targetId: this.getTargetId(embeddings[i]),
+        score,
+      }));
     } catch (error) {
       this.logger.error('Failed to parse rerank results', error);
       // silent error, will fallback to default sorting in parent method
@@ -176,9 +170,9 @@ class ProductionEmbeddingClient extends EmbeddingClient {
 
       const highConfidenceChunks = ranks
         .flat()
-        .toSorted((a, b) => b.scores.score - a.scores.score)
-        .filter(r => r.scores.score > 5)
-        .map(r => chunks[`${r.scores.targetId}:${r.scores.chunk}`])
+        .toSorted((a, b) => b.score - a.score)
+        .filter(r => r.score > 5)
+        .map(r => chunks[`${r.targetId}:${r.chunk}`])
         .filter(Boolean);
 
       this.logger.verbose(

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

@@ -177,11 +177,6 @@ export abstract class EmbeddingClient {
 
 const ReRankItemSchema = z.object({
   scores: z.object({
-    reason: z
-      .string()
-      .describe(
-        'Think step by step, describe in 20 words the reason for giving this score.'
-      ),
     chunk: z.string().describe('The chunk index of the search result.'),
     targetId: z.string().describe('The id of the target.'),
     score: z
@@ -194,11 +189,4 @@ const ReRankItemSchema = z.object({
   }),
 });
 
-export const getReRankSchema = (size: number) =>
-  z.object({
-    ranks: ReRankItemSchema.array().describe(
-      `A array of scores. Make sure to score all ${size} results.`
-    ),
-  });
-
-export type ReRankResult = z.infer<ReturnType<typeof getReRankSchema>>['ranks'];
+export type ReRankResult = z.infer<typeof ReRankItemSchema>['scores'][];