round 1: implement bracket-first manual compaction

packages/goal/goal/tests/goal.spec.ts

@@ -55,6 +55,7 @@ function stubAgentForSession(session: Session): StubAgent {
       if (shouldDefer) deferred.push(input)
       else appendInjection(session, input)
     },
+    reserveTurnAdmission: () => undefined,
     cancel() {},
     whenIdle() { return Promise.resolve() },
   }

packages/goal/goal/tests/projection.spec.ts

@@ -45,6 +45,7 @@ function liveAgent(ctx: Context, session: Session): Agent {
     inject(input: UserMessage) {
       session.append('user/message', input, { surfaceOp: 'append' })
     },
+    reserveTurnAdmission: () => undefined,
     cancel() {},
     whenIdle() { return Promise.resolve() },
   }