Headless Interrupts

"""LangGraph agent for the Human-in-the-Loop (Interrupt-based) booking demo.Defines a backend tool `schedule_meeting(topic, attendee)` that usesLangGraph's `interrupt()` primitive to pause the run and surface astructured booking payload to the frontend. The frontend `useInterrupt`renderer shows a time picker inline in the chat and resolves with`{chosen_time, chosen_label}` or `{cancelled: true}`, which this toolturns into a human-readable result the agent uses to confirm the booking."""from __future__ import annotationsfrom datetime import datetime, time, timedeltafrom typing import Any, List, Optionalfrom zoneinfo import ZoneInfofrom langchain.agents import create_agentfrom langchain_core.tools import toolfrom langchain_openai import ChatOpenAIfrom langgraph.types import interruptfrom copilotkit import CopilotKitMiddlewareSYSTEM_PROMPT = (    "You are a scheduling assistant. Whenever the user asks you to book a "    "call / schedule a meeting, you MUST call the `schedule_meeting` tool. "    "Pass a short `topic` describing the purpose and `attendee` describing "    "who the meeting is with. After the tool returns, confirm briefly "    "whether the meeting was scheduled and at what time, or that the user "    "cancelled.")# Demo-only fixed timezone. A real app would use the user's calendar +# locale (e.g. zoneinfo.ZoneInfo(user.timezone) and Google Calendar /# Outlook availability); we hardcode Pacific so screenshots are stable._DEMO_TZ = ZoneInfo("America/Los_Angeles")def _candidate_slots() -> List[dict]:    """Upcoming candidate slots, relative to "now" so the picker never    shows stale dates."""    now = datetime.now(_DEMO_TZ)    tomorrow = (now + timedelta(days=1)).date()    # Skip a week when the result would collide with `tomorrow` — i.e.    # today is Mon (0 days away, picker would show two slots both    # labelled "Monday") or Sun (1 day away, picker would show    # "Tomorrow" and "Monday" both pointing at the same date).    days_to_monday = (7 - now.weekday()) % 7    if days_to_monday <= 1:        days_to_monday += 7    next_monday = (now + timedelta(days=days_to_monday)).date()    candidates = [        ("Tomorrow 10:00 AM", tomorrow, time(10, 0)),        ("Tomorrow 2:00 PM", tomorrow, time(14, 0)),        ("Monday 9:00 AM", next_monday, time(9, 0)),        ("Monday 3:30 PM", next_monday, time(15, 30)),    ]    return [        {"label": label, "iso": datetime.combine(d, t, _DEMO_TZ).isoformat()}        for label, d, t in candidates    ]@tooldef schedule_meeting(topic: str, attendee: Optional[str] = None) -> str:    """Ask the user to pick a time slot for a call, via an in-chat picker.    Args:        topic: Short human-readable description of the call's purpose.        attendee: Who the call is with (optional).    Returns:        Human-readable result string describing the chosen slot or        indicating the user cancelled.    """    # `interrupt()` pauses the LangGraph run and forwards a structured    # payload to the client. The frontend v2 `useInterrupt` hook renders    # the picker inline in the chat, then calls `resolve(...)` with the    # user's selection — that value comes back here as `response`.    response: Any = interrupt(        {            "topic": topic,            "attendee": attendee,            "slots": _candidate_slots(),        }    )    if isinstance(response, dict):        if response.get("cancelled"):            return f"User cancelled. Meeting NOT scheduled: {topic}"        chosen_label = response.get("chosen_label") or response.get("chosen_time")        if chosen_label:            return f"Meeting scheduled for {chosen_label}: {topic}"    return f"User did not pick a time. Meeting NOT scheduled: {topic}"model = ChatOpenAI(model="gpt-5.4")graph = create_agent(    model=model,    tools=[schedule_meeting],    middleware=[CopilotKitMiddleware()],    system_prompt=SYSTEM_PROMPT,)

What is this?#

useInterrupt's render callback is the 80% path: it keeps the UI glued to a <CopilotChat> transcript and handles "when to show the picker" logic for you. This page covers the escape hatch: a render-less interrupt resolver you assemble from the same primitives useInterrupt uses internally — a pattern that lives anywhere in your React tree, takes any shape you like (button grid, form, modal, keyboard shortcut), and resolves the interrupt without mounting a chat at all.

On LangGraph the underlying primitive is the framework's interrupt() call, surfaced to the client as an on_interrupt custom event. The headless variant subscribes to that event directly and resumes the run by calling copilotkit.runAgent({...}) with the matching resume payload — no chat surface required.

When should I use this?#

Testing / Playwright fixtures — a deterministic, chat-less button grid is easier to drive than a chat surface where the picker only appears after an LLM call.
Non-chat UIs — dashboards, side panels, inspector surfaces, or any place where you want the agent's interrupt without the chat transcript.
Custom flow control — when you need to know exactly when the interrupt arrived (e.g. to gate other UI) and when it was resolved.
Research / debugging — when you want to observe the raw AG-UI custom events without the abstraction layer.

If you just want "a picker in chat", just use useInterrupt.

The primitives#

Under the hood, useInterrupt composes two public APIs:

agent.subscribe({ onCustomEvent, onRunStartedEvent, onRunFinalized, onRunFailed }) — every AbstractAgent exposes an AG-UI event subscription. LangGraph sends the interrupt through as a custom event named on_interrupt with the interrupt(...) payload as event.value.
copilotkit.runAgent({ agent, forwardedProps: { command: { resume, interruptEvent } } }) — the same call useInterrupt's resolve() makes to resume a paused run. Pass your response as resume and the original interrupt event as interruptEvent.

Wrap those in your own hook and you get a render-less equivalent of useInterrupt:

page.tsx

import React, { useEffect, useMemo, useState } from "react";import {  CopilotKit,  CopilotChat,  useAgent,  useConfigureSuggestions,  useCopilotKit,} from "@copilotkit/react-core/v2";import { generateFallbackSlots } from "../_shared/interrupt-fallback-slots";import type { TimeSlot } from "../_shared/interrupt-fallback-slots";const INTERRUPT_EVENT_NAME = "on_interrupt";type InterruptPayload = {  topic?: string;  attendee?: string;  slots?: TimeSlot[];};type InterruptEvent = {  name: string;  value: InterruptPayload;};export default function InterruptHeadlessDemo() {  return (    <CopilotKit runtimeUrl="/api/copilotkit" agent="interrupt-headless">      <Layout />    </CopilotKit>  );}function Layout() {  const { pending, resolve } = useHeadlessInterrupt("interrupt-headless");  useConfigureSuggestions({    suggestions: [      {        title: "Book a call with sales",        message: "Book an intro call with the sales team to discuss pricing.",      },      {        title: "Schedule a 1:1 with Alice",        message: "Schedule a 1:1 with Alice next week to review Q2 goals.",      },    ],    available: "always",  });  return (    <div className="grid h-screen grid-cols-[1fr_420px] bg-[#FAFAFC]">      <AppSurface pending={pending} resolve={resolve} />      <div className="border-l border-[#DBDBE5] bg-white">        <CopilotChat agentId="interrupt-headless" className="h-full" />      </div>    </div>  );}function useHeadlessInterrupt(agentId: string): {  pending: InterruptEvent | null;  resolve: (response: unknown) => void;} {  const { copilotkit } = useCopilotKit();  const { agent } = useAgent({ agentId });  const [pending, setPending] = useState<InterruptEvent | null>(null);  useEffect(() => {    let local: InterruptEvent | null = null;    const sub = agent.subscribe({      onCustomEvent: ({ event }) => {        if (event.name === INTERRUPT_EVENT_NAME) {          // The AG-UI adapter JSON-stringifies interrupt values, so          // parse when the value arrives as a string.          const raw = event.value ?? {};          local = {            name: event.name,            value: (typeof raw === "string"              ? JSON.parse(raw)              : raw) as InterruptPayload,          };        }      },      onRunStartedEvent: () => {        local = null;        setPending(null);      },      onRunFinalized: () => {        if (local) {          setPending(local);          local = null;        }      },      onRunFailed: () => {        local = null;      },    });    return () => sub.unsubscribe();  }, [agent]);  const resolve = useMemo(    () => (response: unknown) => {      const snapshot = pending;      setPending(null);      void copilotkit        .runAgent({          agent,          forwardedProps: {            command: {              resume: response,              interruptEvent: snapshot?.value,            },          },        })        .catch(() => {});    },    [agent, copilotkit, pending],  );  return { pending, resolve };}

A few things this hook is careful about:

It stages the incoming custom event in a local ref and only commits it to React state on onRunFinalized, mirroring useInterrupt, which doesn't surface the interrupt until the run has actually paused (not just when the event fires mid-stream).
onRunStartedEvent clears any stale pending state, so kicking off a new turn always starts from a clean slate.
onRunFailed drops the staged event so a transport hiccup doesn't leave the UI stuck showing a picker for a run that never paused.

Driving it from plain UI#

Once useHeadlessInterrupt returns { pending, resolve }, the rest is just React. The example below uses two buttons to kick off the agent and a button grid to resolve, with no <CopilotChat> and no render prop:

function HeadlessInterruptPanel() {
  const { copilotkit } = useCopilotKit();
  const { agent } = useAgent({ agentId: "interrupt-headless" });
  const { pending, resolve } = useHeadlessInterrupt("interrupt-headless");

  const kickOff = (prompt: string) => {
    agent.addMessage({ id: crypto.randomUUID(), role: "user", content: prompt });
    void copilotkit.runAgent({ agent });
  };

  if (pending) {
    return (
      <div>
        <p>Pick a slot for {pending.value.topic ?? "a call"}:</p>
        {SLOTS.map((s) => (
          <button key={s.iso} onClick={() => resolve({ chosen_time: s.iso, chosen_label: s.label })}>
            {s.label}
          </button>
        ))}
        <button onClick={() => resolve({ cancelled: true })}>Cancel</button>
      </div>
    );
  }

  return <button onClick={() => kickOff("Book a call with sales.")}>Book call</button>;
}

Going further#

Tool-based HITL with useHumanInTheLoop — for LLM-initiated pauses where the model decides on the fly to ask the user, rather than the runtime forcing the pause itself.
useInterrupt — the render-prop version of this page, with enabled gating and handler preprocessing.