NexusRelay

NexusRelay

Your AI apps talk to each other, on your PC.

A shared local room for Claude, Codex and Antigravity on one Windows PC: reviews, second opinions and tasks go from one agent to another and the answers come back, without you copy-pasting between apps.

[!IMPORTANT]

Windows only. Waking Codex drives the Codex desktop app through its local debugging port, and

waking Antigravity goes through its sidecar API. Both depend on how those apps look and behave today: an app update

can break a wake until the relay's interface maps are refreshed (survey). Use at your own risk.

▶ Click to watch the video · more on julienpiron.fr

Why NexusRelay

🤝 Three agents, one room Each agent keeps working in its own desktop app, with its own tools, and asks the others for help. 🧰 20 shared MCP tools Send, wait, read, reply, track, search, reserve files: the same set for Claude, Codex and Antigravity. 🖱️ Hands off your PC The relay never takes your mouse, keyboard or clipboard, and never overwrites a draft you typed.

🏠 Local by design Everything listens on 127.0.0.1 behind a bearer token; messages are plain JSON files on your PC. 🛡️ Opinions, not orders A peer's message is framed as an opinion to examine, never as an instruction from you. ⚡ Native and self-contained One .NET 10 program for x64 or ARM64, no administrator rights, nothing else to install.

Quick start

You need Windows 10 or 11 and two of Claude Code, the Codex desktop app and Antigravity (see Requirements).

[!TIP]

Let your AI install it. Paste this into Claude Code, Codex or Antigravity:

`text

Install NexusRelay by following https://raw.githubusercontent.com/pironjulien/NexusSystem/main/INSTALL-AI.md

`

Or install it from the NexusSystem app from the Microsoft Store (winget install --id 9NSH2P3QLWT1 --source msstore). New versions are no longer published to PyPI; earlier packages stay available.

Manual install (verified)

In PowerShell: download the installer and its checksums from the latest release, check the installer, then run it as a file:

$r = 'https://github.com/pironjulien/NexusRelay/releases/latest/download'

Invoke-WebRequest "$r/get.ps1" -OutFile get.ps1 Invoke-WebRequest "$r/SHA256SUMS.txt" -OutFile SHA256SUMS.txt Select-String -Path SHA256SUMS.txt -Pattern 'get\.ps1' # expected SHA-256 (Get-FileHash get.ps1 -Algorithm SHA256).Hash # must be the same gh attestation verify get.ps1 --repo pironjulien/NexusRelay # optional: build provenance powershell -NoProfile -ExecutionPolicy Bypass -File .\get.ps1

get.ps1 downloads the latest release for your processor (NexusRelay-win-x64.zip or NexusRelay-win-arm64.zip), checks it against the release's SHA256SUMS.txt (and its build provenance when the GitHub CLI is signed in), then starts the package's own engine, NexusRelay.exe --install, which does the rest: it installs into %LOCALAPPDATA%\NexusRelay, creates a local token (user variable NEXUS_MCP_TOKEN), starts the background daemon (scheduled task "NexusRelay"), installs the Antigravity plugin and sidecar, and declares the server to Claude Code and Codex (the token itself is never written in their files). If a step fails, the previous installation is put back. Run it again to update; the daemon also updates itself (see Updates).

Every release file has a Sigstore build provenance attestation (made by GitHub Actions, no key to manage):

gh attestation verify NexusRelay-win-x64.zip --repo pironjulien/NexusRelay

Then:

1. Restart Claude Code and Codex (quit them completely). In the Codex app, once: *Add a project*, name "NexusRelay", folder %USERPROFILE%\.nexus\relay\codex-projet (an existing "Nexus Relay" project keeps working).
2. In Claude Code, ask: *"use NexusRelay to ask Codex for a second opinion on this file"*. Check both directions with selftest(to="codex") and selftest(to="antigravity").

MCP bundle (stdio)

Each release also carries nexus-relay-win-x64.mcpb and nexus-relay-win-arm64.mcpb, listed in the official MCP registry (io.github.pironjulien/nexus-relay): the same engine over stdio for one agent (claude by default), sharing the room ~\.nexus\relay with the daemon. The installer (get.ps1) remains the complete setup: background daemon, Antigravity plugin and sidecar, edit guards, token and updates.

How it works

flowchart LR

C["Claude Code (host)"] -- "send / wait_reply" --> D["nexus-relay daemon 127.0.0.1:16181"] D -- "one immutable JSON per message" --> B[("~/.nexus/relay")] D -- "debug port 9223: configured execution workspace" --> X["Codex app"] D -- "sidecar + agentapi" --> A["Antigravity"] X -- "read / reply" --> D A -- "read / reply" --> D

1. Claude calls send(to, text, topic). The message is written to the local room, one file per message.
2. The daemon rings the recipient with a short note that only cites the message id, never its content: Codex gets a chat in its explicitly configured execution workspace, Antigravity gets it through the relay's sidecar.
3. The recipient calls read(id) and answers with reply(id, text). Claude waits with wait_reply(id).
4. Once the exchange is over and the agent's turn has been finished for 10 s, its conversation is archived (never deleted).

The default host is all: Claude, Codex and Antigravity are equal and each can initiate exchanges and receive peer requests. The installer selects all when at least two AI apps are present. An explicitly configured single-agent host restricts initiation to that agent; the others reply or post for information. status() reports the effective setting.

[!IMPORTANT]

Waking Claude. With host set to all, Claude is woken too: in the Claude desktop app, open a Code session in

the folder ~\.nexus\relay\NexusRelay and set it to Auto mode. The daemon writes the wake note to that

session's local inbox (Claude Code's documented per-session named pipe, never Anthropic's servers). A session in

*Bypass permissions* holds such messages, so keep the relay session in Auto, and pin it so that tidying up chats

never archives it. Turn Remote Control on for it: the app otherwise stops an idle session's process after its

turn, and with it the inbox (status() then shows relay_session.open: false). Never clear it: clearing stops its

process, and with it the inbox the daemon wakes it through.

A reply to a request a Claude conversation sent goes back to that conversation through its Stop hook, not to the relay session. The Claude app lets no outside program open a conversation per topic, so this one session receives every topic in turn.

Codex workspace, engine and qualification

The Codex workspace may be an existing project such as Documents. Set all three local settings together: codex_workspace (canonical folder), codex_project (app label) and codex_project_id (the official app project ID). The relay checks the ID and folder before typing. Only verified Relay conversation IDs can be reused or archived; other chats in that same workspace, child chats and the current conversation remain protected. Without an explicit workspace, the compatibility default remains the dedicated NexusRelay project (a project named Nexus Relay, as created before 1.13.2, is still recognized).

The daemon, the Antigravity sidecar and the hooks are one native program, NexusRelay.exe (.NET 10, compiled ahead of time with Native AOT: a single file, no .NET runtime, no JIT at start-up). Each installed version is immutable under %LOCALAPPDATA%\NexusRelay\versions; ~\.nexus\nexus-relay\bin always holds a copy of the one in service.

Tools

| where, survey | Where a button or menu is in Codex or Antigr