feat(deepagents): add completion notifier middleware for async subagents by hntrl · Pull Request #334 · langchain-ai/deepagentsjs

Hunter Lovell (hntrl) · 2026-03-20T22:48:46Z

Summary

Port of langchain-ai/deepagents#2119 to TypeScript.

Adds a createCompletionNotifierMiddleware that async subagents can use to proactively notify their supervisor when they complete or error -- closing the gap where the supervisor only learns about completion when someone calls check_async_task.

Why

The async subagent protocol is fire-and-forget: the supervisor launches a task and only discovers its outcome when it (or the user) polls via check_async_task. This means the supervisor can't proactively relay results -- the user has to ask. The completion notifier solves this by having the subagent push a notification to the supervisor's thread when it finishes.

Architecture

Supervisor                    Subagent
    |                            |
    |--- start_async_task -----> |
    |<-- task_id (immediately) - |
    |                            |  (working...)
    |                            |  (done!)
    |                            |
    |<-- runs.create(            |
    |      supervisor_thread,    |
    |      "completed: ...")     |
    |                            |
    |  (wakes up, sees result)   |

This is an opt-in middleware added to the subagent's stack, not the supervisor's. The notifier calls runs.create() on the supervisor's thread via the @langchain/langgraph-sdk Client, which queues a new run that wakes the supervisor.

Parent context propagation: parent_thread_id is injected into the subagent's input state by the supervisor's start_async_task tool (from the Python PR). The parentGraphId (supervisor's graph/assistant ID) is passed as a constructor argument since it's static configuration known at deployment time.

Changes

New: `createCompletionNotifierMiddleware` (`libs/deepagents/src/middleware/completion_notifier.ts`)

afterAgent hook sends a completion notification with result summary (truncated to 500 chars)
wrapModelCall hook catches errors and sends an error notification before re-raising
State schema adds parent_thread_id to the subagent's state
Notifies only once per run (guards against duplicates)
Silently no-ops if parent context is missing (subagent launched without a supervisor)
Supports url and headers options for remote supervisors

New: `completion_notifier.test.ts` — 22 unit tests

Tests for extractLastMessage, notifyParent, afterAgent, wrapModelCall
Covers edge cases: missing parent context, duplicate notification guard, error swallowing

Modified: `package.json`

Added @langchain/langgraph-sdk as a required dependency

Exports

createCompletionNotifierMiddleware and CompletionNotifierOptions exported from deepagents top-level and middleware/index.ts

Usage

import { createCompletionNotifierMiddleware, createDeepAgent } from "deepagents";

// Same deployment (ASGI transport):
const notifier = createCompletionNotifierMiddleware({
  parentGraphId: "supervisor",
});

// Remote deployment:
const notifier = createCompletionNotifierMiddleware({
  parentGraphId: "supervisor",
  url: "https://supervisor.langsmith.dev",
});

const agent = createDeepAgent({
  model: "claude-sonnet-4-5-20250929",
  middleware: [notifier],
});

Divergence from Python

The Python implementation uses langgraph-sdk's get_client() with ASGI transport for same-deployment communication. The JS version uses @langchain/langgraph-sdk's Client class with a default localhost URL (http://localhost:8123) when no URL is provided. The parentGraphId parameter matches the Python parent_graph_id constructor arg.

changeset-bot · 2026-03-20T22:48:50Z

🦋 Changeset detected

Latest commit: 628bcfb

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
deepagents	Patch
deepagents-acp	Patch
@deepagents/evals	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

Colin Francis (colifran)

Nice!

pkg-pr-new · 2026-03-24T04:59:42Z

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npm i https://pkg.pr.new/deepagents-acp@334

npm i https://pkg.pr.new/deepagents@334

npm i https://pkg.pr.new/@langchain/sandbox-standard-tests@334

commit: 628bcfb

Port of langchain-ai/deepagents#2119 to TypeScript. Adds a createCompletionNotifierMiddleware that async subagents can use to proactively notify their supervisor when they complete or error, closing the gap where the supervisor only learns about completion when someone calls check_async_task. - New createCompletionNotifierMiddleware with afterAgent and wrapModelCall hooks - Uses @langchain/langgraph-sdk Client to send runs.create() to the supervisor's thread - Reads parent_thread_id from subagent state (injected by start_async_task) - Derives task_id from runtime.configurable.thread_id - Silently no-ops if parent context is missing - Guards against duplicate notifications - 22 unit tests covering all hooks, edge cases, and error paths fix(deepagents): make url required in completion notifier (no ASGI in JS) JS does not have ASGI transport like Python, so the url parameter must be provided explicitly. Removed all ASGI references from docs and the localhost fallback default. fix(deepagents): throw on built-in tool collision (#330) * add error * Create big-horses-fail.md * add config error class * cr --------- Co-authored-by: Christian Bromann <git@bromann.dev> fix(deepagents): use `crypto.randomUUID()` instead of uuid (#336) * fix(deepagents): use crypto.randomUUID() instead of uuid * update pnpm-lock * Create grumpy-weeks-wave.md * Update libs/deepagents/src/middleware/fs.int.test.ts feat(deepagent): add LangSmithSandbox (#324) * feat(deepagent): add LangSmithSandbox * Change deepagents version from patch to minor * format * fix tests * format * make it a patch * cr * cr * fix * cr regen lockfile linting linting add missing url property chore: version packages (#321) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> changeset regen lockfil

…nts (#334) Port of langchain-ai/deepagents#2119 to TypeScript. Adds a createCompletionNotifierMiddleware that async subagents can use to proactively notify their supervisor when they complete or error, closing the gap where the supervisor only learns about completion when someone calls check_async_task. - New createCompletionNotifierMiddleware with afterAgent and wrapModelCall hooks - Uses @langchain/langgraph-sdk Client to send runs.create() to the supervisor's thread - Reads parent_thread_id from subagent state (injected by start_async_task) - Derives task_id from runtime.configurable.thread_id - Silently no-ops if parent context is missing - Guards against duplicate notifications - 22 unit tests covering all hooks, edge cases, and error paths fix(deepagents): make url required in completion notifier (no ASGI in JS) JS does not have ASGI transport like Python, so the url parameter must be provided explicitly. Removed all ASGI references from docs and the localhost fallback default. fix(deepagents): throw on built-in tool collision (#330) * add error * Create big-horses-fail.md * add config error class * cr --------- Co-authored-by: Christian Bromann <git@bromann.dev> fix(deepagents): use `crypto.randomUUID()` instead of uuid (#336) * fix(deepagents): use crypto.randomUUID() instead of uuid * update pnpm-lock * Create grumpy-weeks-wave.md * Update libs/deepagents/src/middleware/fs.int.test.ts feat(deepagent): add LangSmithSandbox (#324) * feat(deepagent): add LangSmithSandbox * Change deepagents version from patch to minor * format * fix tests * format * make it a patch * cr * cr * fix * cr regen lockfile linting linting add missing url property chore: version packages (#321) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> changeset regen lockfil

* Revert "revert: "feat(deepagents): support multimodal files for backends (#298)" (#352)" (#353) This reverts commit 03ea1c9. * revert: "revert: "feat(sdk): add async subagent middleware for remote LangGraph servers (#323)" (#351)" (#354) * Revert "revert: "feat(sdk): add async subagent middleware for remote LangGraph servers (#323)" (#351)" This reverts commit 367e43a. * use any backend protocol * Reapply "chore(deepagents): refactor backend method names - `lsInfo` -> `ls`, …" (#349) (#356) This reverts commit 573479d. * Reapply "chore(sdk): unify sync subagents and async subagents into a single pr…" (#348) (#355) This reverts commit 96dc34c. * chore: align alpha with main (#358) * fix(deepagents): remove orphaned ToolMessages for Gemini compatibility (#335) * fix(deepagents): remove orphaned ToolMessages for Gemini compatibility * Fix ToolMessages for Gemini compatibility --------- Co-authored-by: Christian Bromann <git@bromann.dev> * fix(deepagents): throw on built-in tool collision (#330) * add error * Create big-horses-fail.md * add config error class * cr --------- Co-authored-by: Christian Bromann <git@bromann.dev> * fix(deepagents): use `crypto.randomUUID()` instead of uuid (#336) * fix(deepagents): use crypto.randomUUID() instead of uuid * update pnpm-lock * Create grumpy-weeks-wave.md * Update libs/deepagents/src/middleware/fs.int.test.ts * feat(deepagent): add LangSmithSandbox (#324) * feat(deepagent): add LangSmithSandbox * Change deepagents version from patch to minor * format * fix tests * format * make it a patch * cr * cr * fix * cr * chore: version packages (#321) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> * regen lockfile * fix langsmith tests so that they use backend protocol v2 methods * format --------- Co-authored-by: pawel-twardziak <pawel.twardziak.dev@gmail.com> Co-authored-by: Christian Bromann <git@bromann.dev> Co-authored-by: Maahir Sachdev <maahir.sachdev@langchain.dev> Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> * feat(deepagents): add completion notifier middleware for async subagents (#334) Port of langchain-ai/deepagents#2119 to TypeScript. Adds a createCompletionNotifierMiddleware that async subagents can use to proactively notify their supervisor when they complete or error, closing the gap where the supervisor only learns about completion when someone calls check_async_task. - New createCompletionNotifierMiddleware with afterAgent and wrapModelCall hooks - Uses @langchain/langgraph-sdk Client to send runs.create() to the supervisor's thread - Reads parent_thread_id from subagent state (injected by start_async_task) - Derives task_id from runtime.configurable.thread_id - Silently no-ops if parent context is missing - Guards against duplicate notifications - 22 unit tests covering all hooks, edge cases, and error paths fix(deepagents): make url required in completion notifier (no ASGI in JS) JS does not have ASGI transport like Python, so the url parameter must be provided explicitly. Removed all ASGI references from docs and the localhost fallback default. fix(deepagents): throw on built-in tool collision (#330) * add error * Create big-horses-fail.md * add config error class * cr --------- Co-authored-by: Christian Bromann <git@bromann.dev> fix(deepagents): use `crypto.randomUUID()` instead of uuid (#336) * fix(deepagents): use crypto.randomUUID() instead of uuid * update pnpm-lock * Create grumpy-weeks-wave.md * Update libs/deepagents/src/middleware/fs.int.test.ts feat(deepagent): add LangSmithSandbox (#324) * feat(deepagent): add LangSmithSandbox * Change deepagents version from patch to minor * format * fix tests * format * make it a patch * cr * cr * fix * cr regen lockfile linting linting add missing url property chore: version packages (#321) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> changeset regen lockfil * chore: enter alpha pre-release * chore: target alpha for releases * chore: version packages (alpha) (#359) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> * chore(deepagents): extend supported backend file types (#363) * extend supported file types * Create strong-tigers-share.md --------- Co-authored-by: Hunter Lovell <40191806+hntrl@users.noreply.github.com> * chore(deepagents): implement async subagents + use stream example (#360) * async subagents + use stream example * fix lockfile * format * linting * readme and linting * format * proactively send responses when subagents complete * better examples * feat(deepagents): rename completion notifier to completion callback and align with Python (#361) * feat(deepagents): rename completion notifier to completion callback and align with Python PR - Rename completion_notifier.ts -> completion_callback.ts to match Python's completion_callback.py naming - Rename exports: createCompletionNotifierMiddleware -> createCompletionCallbackMiddleware, CompletionNotifierOptions -> CompletionCallbackOptions - Rename state key: parent_thread_id -> callbackThreadId, option: parentGraphId -> callbackGraphId - Make url optional (Python allows omitting for ASGI transport) - Match Python's strict error behavior: throw on empty messages, non-AIMessage types, and missing callbackThreadId - Add truncation suffix with task_id hint for long messages - Use generic error message in wrapModelCall (don't leak error details) - Remove duplicate notification guard (Python notifies on every error) - Add extractCallbackContext to async_subagents.ts: injects callbackThreadId into subagent input state when launching via start_async_task - Add tests for extractCallbackContext and callback context injection * cr * Rename completion notifier to completion callback Renamed completion notifier to completion callback for consistency with Python. * fix(sdk): `AsyncTask` `updatedAt` field doesn't update on task status changes (#400) * update updatedAt field to change on any task update * added changeset * chore: set up self hosted async subagent example (#399) * self hosted async subagent example * with postgres * formatting * eslint disable no console * fix dockerfile and readme * Update examples/async-subagent-server/server.ts Co-authored-by: Christian Bromann <git@bromann.dev> --------- Co-authored-by: Christian Bromann <git@bromann.dev> * chore(sdk): update async subagent middleware for agent protocol (#394) * update async subagent middleware for agent protocol * add changeset * Update libs/deepagents/src/middleware/async_subagents.ts Co-authored-by: Hunter Lovell <40191806+hntrl@users.noreply.github.com> * Update libs/deepagents/src/middleware/async_subagents.ts Co-authored-by: Hunter Lovell <40191806+hntrl@users.noreply.github.com> * Update libs/deepagents/src/middleware/async_subagents.ts Co-authored-by: Hunter Lovell <40191806+hntrl@users.noreply.github.com> * differentiate agent protocol --------- Co-authored-by: Hunter Lovell <40191806+hntrl@users.noreply.github.com> * chore(repo): migrate linting and formatting to oxc tooling (#391) * chore(repo): migrate linting and formatting to oxc tooling * cr * cr * chore(lint): clean up console disables for oxlint * cr * Apply suggestions from code review Co-authored-by: Christian Bromann <git@bromann.dev> --------- Co-authored-by: Christian Bromann <git@bromann.dev> * refactor(deepagents): clean up createDeepAgent middleware wiring (#392) * refactor(deepagents): clean up createDeepAgent middleware wiring * fix(deepagents): avoid duplicate HITL middleware on subagents * add comments, remove iife * Create ten-masks-flow.md * fix(deepagents): align prompt templates with runtime behavior (#393) * fix(deepagents): align prompt templates with runtime behavior * chore: add changeset for prompt alignment fixes * cr * cr * fix store backend and tests * lint * fix rests and resolveBackend * lint * fix failing tests * revert adapt resolve backend * fix resolve backend * better variable name * fix backend factory to return a maybe promise * mark resolve backend as internal * format --------- Co-authored-by: Colin Francis <131073567+colifran@users.noreply.github.com> Co-authored-by: pawel-twardziak <pawel.twardziak.dev@gmail.com> Co-authored-by: Christian Bromann <git@bromann.dev> Co-authored-by: Maahir Sachdev <maahir.sachdev@langchain.dev> Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> Co-authored-by: Colin Francis <colin.francis@langchain.dev>

Colin Francis (colifran) approved these changes Mar 20, 2026

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Colin Francis (colifran) force-pushed the hunter/js-notifier-middleware branch from db2c8b5 to ffe73d8 Compare March 24, 2026 04:49

Colin Francis (colifran) changed the base branch from main to 1.9.0-alpha.1 March 24, 2026 17:23

Colin Francis (colifran) force-pushed the hunter/js-notifier-middleware branch from bc480e8 to 13e1b3b Compare March 24, 2026 18:09

Colin Francis (colifran) force-pushed the hunter/js-notifier-middleware branch from 45900bf to 628bcfb Compare March 24, 2026 18:26

Colin Francis (colifran) merged commit 050d52c into 1.9.0-alpha.1 Mar 24, 2026
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Colin Francis (colifran) deleted the hunter/js-notifier-middleware branch March 24, 2026 18:34

Hunter Lovell (hntrl) mentioned this pull request Apr 1, 2026

chore: merge alpha into main #404

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feat(deepagents): add completion notifier middleware for async subagents#334

feat(deepagents): add completion notifier middleware for async subagents#334
Colin Francis (colifran) merged 1 commit into1.9.0-alpha.1from
hunter/js-notifier-middleware

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Hunter Lovell (hntrl) commented Mar 20, 2026

Summary

Why

Architecture

Changes

New: createCompletionNotifierMiddleware (libs/deepagents/src/middleware/completion_notifier.ts)

New: completion_notifier.test.ts — 22 unit tests

Modified: package.json

Exports

Usage

Divergence from Python

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New: `createCompletionNotifierMiddleware` (`libs/deepagents/src/middleware/completion_notifier.ts`)

New: `completion_notifier.test.ts` — 22 unit tests

Modified: `package.json`

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