chopin

A collaborative plan, written by a team and an agent together.

Several people edit one MDX document at once, with cursors and presence. A planning agent reads the selected GitHub repository, writes into the same document, and asks the channel when something cannot be settled from the code alone. Answers are attributed to the GitHub user who made them and linked to the prose they produced.

Running it

Chopin requires Bun 1.3.2, PostgreSQL, and a GitHub App. The Bun version matches CI and the production image; verify it with bun --version. Register these URLs on a GitHub App owned by the deployment:

Homepage:  http://127.0.0.1:8787
Callback:  http://127.0.0.1:8787/auth/github/callback
Setup URL: http://127.0.0.1:8787/auth/github/setup

Enable expiring user authorization tokens, disable OAuth during installation, and grant read access to Contents, Pull requests, Checks, and Commit statuses. Make the App installable on any account and disable webhooks. See Authentication for the complete registration values.

Then configure and start the service:

bun install
cp .env.example .env
# Fill in the GitHub App slug, client credentials, and session key in .env.
bun run db:up
bun run migrate
bun run dev

Open http://127.0.0.1:8787, sign in with GitHub, choose a repository, and create a planning channel. Open that channel in another browser profile to see the multiplayer half. Ctrl-C stops the web and server processes; bun run db:down stops PostgreSQL.

Set AGENT=off to run the editor without Copilot.

For proxied VM development and remote HMR, see Remote development.

Docker

The production image builds the browser client and serves it from the same Bun process that owns the API and WebSocket. To run the complete stack locally, fill in the GitHub App and session variables in .env, then run:

bun run docker:up

This builds the image, starts PostgreSQL, applies migrations, and listens on http://127.0.0.1:8787. bun run docker:down stops the stack. The ordinary bun run db:up remains database-only for development with Vite HMR.

For a deployment using a managed database, build Dockerfile, provide DATABASE_URL, APP_ORIGIN, the GitHub App credentials and slug, and SESSION_ENCRYPTION_KEY at runtime, and expose container port 8787. Do not bake .env or any credential into the image.

Talking to the agent

The agent acts only when addressed:

should we cover the export format?     -> the channel only
yes, Markdown for now                  -> the channel only
@ai                                    -> acts on the conversation above
@ai draft the export section           -> acts on that

Anything said without the mention is still carried into the agent's next turn, so a team can settle something between themselves and the agent arrives already knowing. The composer says which destination a message has before you send it.

The first editor to invoke the planner lends their GitHub App session to that channel's Copilot usage. The agent receives repository-scoped read tools and no host filesystem or shell. New planner session releases ownership so another editor can take it. Login sessions and GitHub credentials exist only in the server process; restarting Chopin signs everyone out and releases Planner ownership without losing plans or transcripts.

Configuration

Variable	Default	Meaning
DATABASE_URL	required	PostgreSQL connection URL; never printed by the server.
STORAGE_DRIVER	postgres	Built-in storage adapter.
APP_ORIGIN	required	Exact public HTTP(S) origin used for callbacks and Origin checks.
GITHUB_APP_SLUG	required	Slug from the GitHub App's public link.
GITHUB_APP_CLIENT_ID	required	GitHub App OAuth client id, distinct from the App id.
GITHUB_APP_CLIENT_SECRET	required	GitHub App client secret used for user-token exchange and refresh.
SESSION_ENCRYPTION_KEY	required	32 random bytes as 64 hex characters; encrypts OAuth state and PKCE.
SERVER_HOST	127.0.0.1	Bind address.
PORT	8787	HTTP and WebSocket port.
MODEL	claude-sonnet-4.6	Planner model.
AGENT	on	AGENT=off hides and disables the planner.

Generate the session key with openssl rand -hex 32. APP_ORIGIN has no trailing slash and must match the GitHub App callback's origin exactly.

Sharing

The client derives the application socket from the page origin, so a tunnel needs no separate application WebSocket setting:

SERVER_HOST=0.0.0.0 APP_ORIGIN=https://chopin.example bun run dev
cloudflared tunnel --url http://127.0.0.1:8787

Update the GitHub App homepage, callback, and setup URL to the new origin. Every participant authorizes the App, and an account owner installs it on the selected repositories. Repository access is checked before a channel is listed, opened, or edited. This single-port example does not carry remote Vite HMR; see Remote development for that setup.

Architecture

packages/dialect     the plan's MDX dialect and Lexical schema
packages/question    questionnaires: definition, shared answer, derivation
packages/editor      the browser editor, cursors, decisions pane
packages/protocol    wire types and addressing rules
packages/viewport    browser viewport geometry and event subscriptions
apps/server          auth, channels, documents, persistence, the agent
apps/web             repositories, channels, and the three-pane workspace

The server holds every open channel as a Yjs document with a headless Lexical editor bound to it. That mirror lets it validate an edit rather than relay bytes it cannot read. Accepted updates and sidecar state are committed to PostgreSQL before acknowledgement; complete checkpoints retain canonical MDX and the Yjs epoch for recovery.

See Document architecture, Authentication, Repository channels, Storage adapters, and Copilot agent.

Three things are worth knowing before changing it:

• The dialect is an allowlist. Plan content is parsed and rendered, never evaluated.
• Repository authorization is the boundary. HTTP routes, WebSocket upgrades, and agent tools recheck the owning GitHub session and repository permission.
• An unhandled node type kills collaboration silently. registry.test.ts asserts that every dialect node can be serialized and synchronized.

Development

bun test              # unit and in-memory adapter tests, no browser or agent
bun run test:postgres # storage contract against PostgreSQL
bun run e2e           # fake GitHub, real auth/session/channel path, Chromium
bun run types         # every package and e2e
bun run ci            # formatting, lint, and token checks
bun run build         # production client
bun run start         # serve the built client

The browser suite needs Chromium once with bun run e2e:browsers. It starts two temporary PostgreSQL services, migrates them, builds the client, and runs with AGENT=off. Its fake GitHub implementation replaces only GitHub's network responses; OAuth state, process-local sessions, repository authorization, channel routes, WebSockets, and persistence are the production implementations.

AGENTS.md is the companion for maintainers: invariants, deliberate decisions, and failure modes that are otherwise easy to miss.

Origins

The dialect, editor, and questionnaire model began as a port of Ace's plan feature and were restructured around authenticated repository channels, durable storage, and a repository-scoped agent. Work happens here now.