diff --git a/scripts/mutation-gate.mjs b/scripts/mutation-gate.mjs
index cb691c88..6317e387 100644
--- a/scripts/mutation-gate.mjs
+++ b/scripts/mutation-gate.mjs
@@ -7260,6 +7260,18 @@ const MUTANT_DEFINITIONS = [
       replace: "    _serverCfg: { state: true },\n    _devices: { state: true },",
     }],
   },
+  {
+    id: 'adoption-notifies-no-host-on-config-replacement',
+    guard: 'node --test test/config-adoption.test.mjs',
+    because: 'since #520 the bodies are no longer declared Lit properties, so this call is the '
+      + 'only thing that wakes an update when the config body is replaced: without it the '
+      + 'geometry epoch never moves and the plan keeps painting the retired body (#520 AC2)',
+    patches: [{
+      file: 'src/config-adoption.ts',
+      find: "    this.config = next;\n    this.onBodyReplaced?.('_serverCfg', previous);",
+      replace: '    this.config = next;',
+    }],
+  },
   {
     id: 'live-editor-view-mode-routes-live',
     guard: 'node --test test/live-editor.test.mjs',