fix(acp): scope connection-owned continuation drain

packages/subagent/subagent/src/index.ts

@@ -215,6 +215,23 @@ export class SubagentService extends Service {
     await manager.drain()
   }
 
+  /**
+   * Close continuable admission below exact live parent Agents, stop only their
+   * visible descendant Activations synchronously, then await admitted scoped
+   * materializations and release those forests child-first. The scoped cutoff
+   * lasts until each exact parent leaves the registry; unrelated parent trees
+   * remain live.
+   * @param parents - exact host-owned parent Agents entering teardown.
+   * @returns once every retained descendant Activation released its `AgentHandle`.
+   * @throws an aggregate error after all scoped branches settle when any failed.
+   */
+  async drainContinuableDescendants(parents: readonly Agent[]): Promise<void> {
+    const manager = this.continuations
+    // Absent continuation services means nothing was ever materialized.
+    if (manager === undefined) return
+    await manager.drainDescendants(parents)
+  }
+
   /**
    * Register a provider under its name. Registration is effect-scoped and HMR
    * safe; removing a provider blocks new starts but does not revoke runs that