fix(subagents): return completion message for manual session spawns

src/agents/tools/sessions-spawn-tool.ts

@@ -1,8 +1,8 @@
 import { Type } from "@sinclair/typebox";
 import type { GatewayMessageChannel } from "../../utils/message-channel.js";
+import type { AnyAgentTool } from "./common.js";
 import { optionalStringEnum } from "../schema/typebox.js";
 import { spawnSubagentDirect } from "../subagent-spawn.js";
-import type { AnyAgentTool } from "./common.js";
 import { jsonResult, readStringParam } from "./common.js";
 
 const SessionsSpawnToolSchema = Type.Object({
@@ -66,6 +66,7 @@ export function createSessionsSpawnTool(opts?: {
           thinking: thinkingOverrideRaw,
           runTimeoutSeconds,
           cleanup,
+          expectsCompletionMessage: true,
         },
         {
           agentSessionKey: opts?.agentSessionKey,