round 1: implement bracket-first manual compaction

packages/fs/tool-str-replace-editor/tests/tools.spec.ts

@@ -40,6 +40,7 @@ function agent(ctx: Context, cwd: string): Agent {
     inject: () => {},
     send: () => {},
     updateInbox: () => 'not-found',
+    reserveTurnAdmission: () => undefined,
     cancel() {},
     whenIdle: () => Promise.resolve(),
   }