feat: add indexUid to SearchMetadata

- Add indexUid field to SearchMetadata struct
- Update perform_search to include indexUid in metadata
- Update federated search to include indexUid for each query

The metadata field now contains both queryUid and indexUid:
- For /search: single object with queryUid and indexUid
- For /multi-search: each result has metadata with both fields
- For federated search: array of objects, each with queryUid and indexUid

crates/meilisearch/src/search/federated/perform.rs

@@ -63,7 +63,8 @@ pub async fn perform_federated_search(
     let mut query_metadata = Vec::new();
     for (query_index, federated_query) in queries.into_iter().enumerate() {
         let query_uid = Uuid::now_v7();
-        query_metadata.push(SearchMetadata { query_uid });
+        query_metadata
+            .push(SearchMetadata { query_uid, index_uid: federated_query.index_uid.to_string() });
         partitioned_queries.partition(federated_query, query_index, &network, features)?
     }
 

crates/meilisearch/src/search/mod.rs

@@ -841,6 +841,7 @@ pub struct SearchHit {
 #[schema(rename_all = "camelCase")]
 pub struct SearchMetadata {
     pub query_uid: Uuid,
+    pub index_uid: String,
 }
 
 #[derive(Serialize, Clone, PartialEq, ToSchema)]
@@ -1143,6 +1144,7 @@ pub fn perform_search(
     request_uid: Uuid,
 ) -> Result<SearchResult, ResponseError> {
     let before_search = Instant::now();
+    let index_uid_for_metadata = index_uid.clone();
     let rtxn = index.read_txn()?;
     let time_budget = match index.search_cutoff(&rtxn)? {
         Some(cutoff) => TimeBudget::new(Duration::from_millis(cutoff)),
@@ -1163,7 +1165,7 @@ pub fn perform_search(
             query_vector,
         },
         semantic_hit_count,
-    ) = search_from_kind(index_uid, search_kind, search)?;
+    ) = search_from_kind(index_uid.clone(), search_kind, search)?;
 
     let SearchQuery {
         q,
@@ -1260,7 +1262,7 @@ pub fn perform_search(
         used_negative_operator,
         semantic_hit_count,
         request_uid: Some(request_uid),
-        metadata: Some(SearchMetadata { query_uid }),
+        metadata: Some(SearchMetadata { query_uid, index_uid: index_uid_for_metadata }),
     };
     Ok(result)
 }