--- title: Sub-agent RPC and programmatic turns description: Stream Think turns through a child agent with chat(), and trigger turns programmatically with saveMessages(), continueLastTurn(), and abort. image: https://developers.cloudflare.com/dev-products-preview.png --- > Documentation Index > Fetch the complete documentation index at: https://developers.cloudflare.com/agents/llms.txt > Use this file to discover all available pages before exploring further. [Skip to content](#%5Ftop) # Sub-agent RPC and programmatic turns Think works as both a top-level agent and a sub-agent. When used as a sub-agent, the `chat()` method runs a full turn and streams events via a callback. Note This page covers calling Think from server code instead of a browser โ€” multi-agent systems, scheduled or webhook-triggered turns, and recovery. If you are building a single chat agent that users talk to in the browser, you can skip it; `useAgentChat` (see [Getting started](https://developers.cloudflare.com/agents/harnesses/think/getting-started/)) is all you need. For durable acceptance with idempotent retry and later status inspection, refer to [Programmatic submissions](https://developers.cloudflare.com/agents/harnesses/think/programmatic-submissions/). For recovery after eviction, refer to [Durable recovery](https://developers.cloudflare.com/agents/harnesses/think/recovery/). ## chat TypeScript ``` async chat( userMessage: string | UIMessage, callback: StreamCallback, options?: ChatOptions,): Promise ``` ### StreamCallback | Method | When it fires | | ---------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | onStart(event) | Before work starts; exposes the request ID for cancellation | | onEvent(json) | For each streaming chunk (JSON-serialized UIMessageChunk) | | onDone() | After the turn completes and the assistant message is persisted | | onError(message) | On error during the turn | | onInterrupted() | Optional. The attempt was interrupted and a scheduled continuation (in a later isolate) owns the final outcome โ€” not done, not a terminal error. Defaults to a no-op | `onInterrupted` matters for a `chat()`\-driven turn that is interrupted and recovers: the RPC promise resolves **cleanly** (the isolate is still alive), so a consumer that keys off the clean resolve would mis-read it as success and finalize whatever partial it had streamed. Treat it as "not done, not failed โ€” a continuation owns the answer": keep the channel open, show a recovering state, or re-attach, rather than finalizing the partial. A deploy or eviction interruption kills the isolate before this can fire (the caller sees a transport break instead); `onInterrupted` covers the in-isolate stall-into-recovery path. ### ChatOptions | Field | Description | | ------ | ----------------------------------------- | | signal | AbortSignal to cancel the turn mid-stream | Tools belong to the child agent. Define durable capabilities with the child's `getTools()`, extensions, MCP tools, or client tool schemas. Legacy callers that pass `options.tools` to `chat()` receive a warning and the value is ignored. ### Example: parent calling a child * [ JavaScript ](#tab-panel-5881) * [ TypeScript ](#tab-panel-5882) JavaScript ``` import { Think } from "@cloudflare/think"; export class ParentAgent extends Think { getModel() { /* ... */ } async delegateToChild(task) { const child = await this.subAgent(ChildAgent, "child-1"); const chunks = []; await child.chat(task, { onStart: (event) => { console.log("Child started:", event.requestId); }, onEvent: (json) => { chunks.push(json); }, onDone: () => { console.log("Child completed"); }, onError: (error) => { console.error("Child failed:", error); }, }); return chunks; }} export class ChildAgent extends Think { getModel() { /* ... */ } getSystemPrompt() { return "You are a research assistant. Analyze data and report findings."; }} ``` TypeScript ``` import { Think } from "@cloudflare/think";import type { StreamCallback } from "@cloudflare/think"; export class ParentAgent extends Think { getModel() { /* ... */ } async delegateToChild(task: string) { const child = await this.subAgent(ChildAgent, "child-1"); const chunks: string[] = []; await child.chat(task, { onStart: (event) => { console.log("Child started:", event.requestId); }, onEvent: (json) => { chunks.push(json); }, onDone: () => { console.log("Child completed"); }, onError: (error) => { console.error("Child failed:", error); }, }); return chunks; }} export class ChildAgent extends Think { getModel() { /* ... */ } getSystemPrompt() { return "You are a research assistant. Analyze data and report findings."; }} ``` ### Cancelling a sub-agent turn Use `onStart` and `cancelChat()` for RPC-safe cancellation across a sub-agent boundary: * [ JavaScript ](#tab-panel-5877) * [ TypeScript ](#tab-panel-5878) JavaScript ``` let requestId; const callback = { onStart(event) { requestId = event.requestId; }, onEvent(json) { // Forward stream chunks. }, onDone() {}, onError(error) { console.error(error); },}; const turn = child.chat("Long analysis task", callback); // Later, from another RPC call or failure handler:if (requestId) { await child.cancelChat(requestId, "client disconnected");} await turn; ``` TypeScript ``` let requestId: string | undefined; const callback: StreamCallback = { onStart(event) { requestId = event.requestId; }, onEvent(json) { // Forward stream chunks. }, onDone() {}, onError(error) { console.error(error); },}; const turn = child.chat("Long analysis task", callback); // Later, from another RPC call or failure handler:if (requestId) { await child.cancelChat(requestId, "client disconnected");} await turn; ``` If the caller and callee are not separated by Workers RPC, you can also pass an `AbortSignal` to cancel mid-stream: * [ JavaScript ](#tab-panel-5871) * [ TypeScript ](#tab-panel-5872) JavaScript ``` const controller = new AbortController();setTimeout(() => controller.abort(), 30_000); await child.chat("Long analysis task", callback, { signal: controller.signal,}); ``` TypeScript ``` const controller = new AbortController();setTimeout(() => controller.abort(), 30_000); await child.chat("Long analysis task", callback, { signal: controller.signal,}); ``` `cancelChat(requestId, reason?)` is a no-op if the turn already completed or the request ID is unknown. When aborted, the partial assistant message is still persisted. ## saveMessages Inject messages and trigger a model turn without a WebSocket connection. Use for scheduled responses, webhook-triggered turns, proactive agents, or chaining from `onChatResponse`. TypeScript ``` async saveMessages( messages: | UIMessage[] | ((current: UIMessage[]) => UIMessage[] | Promise), options?: SaveMessagesOptions,): Promise ``` Returns `{ requestId, status, error? }` where `status` is `"completed"`, `"error"`, `"skipped"`, or `"aborted"`. | status | When | | ----------- | --------------------------------------------------------------------------------------------------------------------- | | "completed" | Turn ran to completion. | | "error" | Turn started but the stream reported an error. error contains the stream error message when available. | | "skipped" | Turn invalidated mid-flight, for example by chat-clear; user message persisted, no model run. | | "aborted" | Turn cancelled before completion via options.signal or chat-request-cancel. Partial assistant chunks still persisted. | Pass `options.signal` to cancel a programmatic turn from the Durable Object that starts it. `AbortSignal` cannot cross Durable Object RPC boundaries, and the signal is not persisted across hibernation. ### Static messages * [ JavaScript ](#tab-panel-5873) * [ TypeScript ](#tab-panel-5874) JavaScript ``` await this.saveMessages([ { id: crypto.randomUUID(), role: "user", parts: [{ type: "text", text: "Time for your daily summary." }], },]); ``` TypeScript ``` await this.saveMessages([ { id: crypto.randomUUID(), role: "user", parts: [{ type: "text", text: "Time for your daily summary." }], },]); ``` ### Function form When multiple `saveMessages` calls queue up, the function form runs with the latest messages when the turn actually starts: * [ JavaScript ](#tab-panel-5875) * [ TypeScript ](#tab-panel-5876) JavaScript ``` await this.saveMessages((current) => [ ...current, { id: crypto.randomUUID(), role: "user", parts: [{ type: "text", text: "Continue your analysis." }], },]); ``` TypeScript ``` await this.saveMessages((current) => [ ...current, { id: crypto.randomUUID(), role: "user", parts: [{ type: "text", text: "Continue your analysis." }], },]); ``` ### Scheduled responses Trigger a recurring prompt turn with [getScheduledTasks()](https://developers.cloudflare.com/agents/harnesses/think/scheduled-tasks/): * [ JavaScript ](#tab-panel-5879) * [ TypeScript ](#tab-panel-5880) JavaScript ``` export class MyAgent extends Think { getModel() { /* ... */ } getScheduledTasks() { return { dailyReport: { schedule: "every day at 09:00", timezone: "UTC", prompt: "Generate the daily report.", }, }; }} ``` TypeScript ``` export class MyAgent extends Think { getModel() { /* ... */ } getScheduledTasks() { return { dailyReport: { schedule: "every day at 09:00", timezone: "UTC", prompt: "Generate the daily report.", }, }; }} ``` ### Chaining from onChatResponse Start a follow-up turn after the current one completes: TypeScript ``` async onChatResponse(result: ChatResponseResult) { if (result.status === "completed" && this.needsFollowUp(result.message)) { await this.saveMessages([{ id: crypto.randomUUID(), role: "user", parts: [{ type: "text", text: "Now summarize what you found." }], }]); }} ``` ## continueLastTurn Run another model call after the latest assistant message without injecting a new user message. Think persists the result as a new assistant message with `continuation: true`; it does not append chunks to the existing assistant message. TypeScript ``` protected async continueLastTurn( body?: Record, options?: SaveMessagesOptions,): Promise ``` Returns `{ requestId, status: "skipped" }` if the last message is not an assistant message. The optional `body` parameter overrides the stored body for this continuation. Pass `options.signal` to cancel the continuation while it is running. ## abortRequest and abortAllRequests Cancel in-flight chat turns from inside the Durable Object: TypeScript ``` protected abortRequest(requestId: string, reason?: unknown): voidprotected abortAllRequests(): void ``` Use `abortRequest()` when you know the request ID. Use `abortAllRequests()` for single-purpose helpers that should cancel whatever turn is currently running. 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