fix(elysia): improve span filtering for function handlers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: logaretm

packages/elysia/src/withElysia.ts

@@ -99,11 +99,18 @@ export function withElysia<T extends Elysia>(app: T, options?: Partial<ElysiaHan
       });
 
       // Filter out the empty spans we marked above before sending the transaction,
-      // then clear the set to avoid unbounded memory growth.
+      // and delete matched IDs individually to avoid clearing IDs from concurrent transactions.
       client.on('beforeSendEvent', event => {
         if (event.type === 'transaction' && event.spans) {
-          event.spans = event.spans.filter(span => !emptySpanIds.has(span.span_id));
-          emptySpanIds.clear();
+          event.spans = event.spans.filter(span => {
+            if (!emptySpanIds.has(span.span_id)) {
+              return true;
+            }
+
+            emptySpanIds.delete(span.span_id);
+
+            return false;
+          });
         }
       });
     }