XoverClient joined all received pieces into one buffer on every arrival (quadratic for a 2.6 MB reply), and turned the inflated check into text the raw path doesn't use. The coordinator under load (3 workers, 4 connections): busy 40% → 13% of a core, Buffer.concat gone from the profile. (master's relay uses the same client.) Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>