refactor(agent-loop): simplify message machine

packages/core/agent-loop/src/index.ts

@@ -384,18 +384,7 @@ export class AgentLoop extends Service implements AgentFactory {
         if (machine === undefined) await machineReady.promise
         if (machine !== undefined) {
           machine.cancel({ kind: 'disposed' })
-          // Drain to TRUE quiescence: cancel's own synchronous event chain
-          // (running→idle) can legitimately re-enter through an automation
-          // listener (goal-session's idle drive) and replace `done` with a
-          // fresh admission before this await captures it. The replacement
-          // work is cancelled and drained in turn until the slot stabilizes.
-          let done = machine.done
-          while (true) {
-            await Promise.allSettled([done])
-            if (machine.done === done) break
-            done = machine.done
-            machine.cancel({ kind: 'disposed' })
-          }
+          await machine.whenIdle()
           await machine.scope.dispose()
         }
       } finally {
@@ -452,7 +441,7 @@ export class AgentLoop extends Service implements AgentFactory {
           loopCtx.agents.announce(agent)
           assertLive()
           // A synchronous announce/session-start listener may have started
-          // teardown; the machine is already live (send() works from the
+          // teardown; the machine is already live (delivery works from the
           // session-start seam), so only the liveness recheck is owed.
           emitAgentEvent(loopCtx, agent, 'agent/session-start', source)
           assertLive()