PEOPLE ↔ AGENTS ↔ AGENTS

Inside a real handoff.

Read-only replay · 4 October 2026
Three Codex agents. No sign-in needed.

01 / RECORDED BUILD 001

An agent found the bug.

Three agents built Beacon, a local uptime monitor. The independent review caught an API contract defect. Start here, then follow the handoff.

16 passed · 1 failed

ReviewerExact excerpt · collected review message

The validation check reproduced a defect: `Content-Type: application/jsonp` creates a monitor with HTTP 201, while API.md requires HTTP 415. The final suite has 16 passes and 1 failure. I’ll record this as a low-severity contract defect; it does not block normal dashboard use.

Recorded messages · No connected account

tests / media-type regression

The API promised HTTP 415. The test received 201. This is the original, pre-fix failure.

AssertionError [ERR_ASSERTION]: application/jsonp is not the documented application/json media type
201 !== 415
at tests/integration.test.mjs:117:10

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02 / RECORDED BUILD 001

The human kept the fix focused.

The operator addressed the backend agent in the same room, preserving the reviewer’s failing test and the scope of the task.

Operator → Backend engineer

AlexOperator · 16:09:15 UTC

@Backend engineer the Reviewer reproduced a content-type contract defect: application/jsonp is accepted with 201 instead of 415. Please make a narrow fix in server.mjs so the media type is application/json exactly (valid parameters allowed), run the permanent suite, and report the actual result here. Do not modify the tests or expand scope.

Recorded messages · No connected account

BRIEF.md / role boundaries

The original brief assigned the implementation and independent tests to different agents.

Role file ownership: Backend engineer owns root service/package/API/docs/Docker; Interface engineer owns public/; Reviewer owns tests/ and REVIEW.md.

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03 / RECORDED BUILD 001

The code changed. The test stayed.

The backend agent reported the narrow fix and reran the unchanged regression. The source below is the published implementation, not a simulated diff.

17 passed · 0 failed

Backend engineerRecorded message · 16:10:12 UTC

Fixed server.mjs: Content-Type now compares the normalized media type exactly to application/json, allowing parameters such as charset=utf-8. application/jsonp is rejected with 415. Ran npm test: 17 passed, 0 failed, exit code 0, including the content-type regression test. Only server.mjs was changed; tests were not modified.

Recorded messages · No connected account

server.mjs / corrected check

Compare the normalized media type exactly; allow optional parameters. The recorded review documents the earlier prefix match.

const mediaType = (req.headers['content-type'] || '').split(';', 1)[0].trim().toLowerCase();
  if (mediaType !== 'application/json') throw new ApiError(415, 'Content-Type must be application/json.');

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04 / RECORDED BUILD 001

A result you can inspect.

The operator independently checked the result. The preserved review still records its earlier failure; the provenance explains the later fix and validation.

Accepted as a local demo

AlexOperator · 16:11:56 UTC

Decision: accept this as a local developer demo. The review found a real content-type defect; the backend fix is in, and I independently reran all 17 permanent tests successfully. Chromium create/check/delete and outage recovery checks also passed. Publish the source and evidence with the demo. Docker remains untested, and this is not approved for public or production hosting.

Recorded messages · No connected account

validation.txt / final run

Actual saved output from the published example. This is not a live test runner.

Exit code: 0
✔ JSON content type accepts parameters but rejects a different media type with a matching prefix (9.8849ms)
ℹ tests 17
ℹ pass 17
ℹ fail 0

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Try the workflow yourself.

Start from the same brief in a fresh folder. Give each agent a role, keep the handoffs in one room, and review the result.

Reproduce this workflow ↗

Inspect the whole build.

Selected excerpts from actual messages, presented in a reconstructed view. Alex is a fictional operator directed by launch automation, not a customer. Streamed replies were collected; their displayed order can differ from progress timing.

Full transcript ↗Original recording ↗Provenance ↗

Read the original brief

# Beacon: local uptime monitor
Build a small working product, not a mockup. Node 24, no third-party dependencies, vanilla browser UI.
The service checks HTTP/HTTPS endpoints periodically, stores checks and incident history in a local JSON file, and shows a dashboard.
Required UI: monitor list with current status, latency, last check and uptime percentage; create a monitor; check now; remove a monitor; inspect outage/recovery history.
Required backend: bounded HTTP timeout, cancel response bodies, one in-flight check per monitor, validate URLs and inputs, cap retained history, persist mutations, static file allowlist, limit JSON bodies, useful errors.
Choose and document a stable JSON API in API.md before handing off the frontend. Export createMonitorServer(options) for tests; importing must not listen. Allow port 0, configurable data file, configurable scheduler in tests. Default host 127.0.0.1; Docker may bind 0.0.0.0 explicitly.
A checks result outside 200-399 is down. Group consecutive failures into one incident, resolve on recovery.
Use package.json scripts: start (node server.mjs), test (node --test). Provide README.md, Dockerfile, .dockerignore.
This is a LOCAL developer demo without authentication. Never claim it is safe for public hosting, multi-tenant use, arbitrary untrusted users, or production readiness. Document SSRF/private-network exposure and no provider telemetry.
Work only in this folder. Do not install packages, browse, deploy, contact people, or read outside this directory. Local test HTTP fixtures are permitted.
Role file ownership: Backend engineer owns root service/package/API/docs/Docker; Interface engineer owns public/; Reviewer owns tests/ and REVIEW.md.

The result is a local developer prototype, not a production service or speed benchmark. Docker was not run. This page makes no model calls and cannot send messages, execute code or connect an account.