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AGENTS.md

This file provides guidance to AI coding agents when working with code in this repository.

Project Overview

exo is a distributed AI inference system that connects multiple devices into a cluster. It enables running large language models across multiple machines using MLX as the inference backend and libp2p for peer-to-peer networking.

Build & Run Commands

# Build the dashboard (required before running exo)
cd dashboard && npm install && npm run build && cd ..

# Run exo (starts both master and worker with API at http://localhost:52415)
uv run exo

# Run with verbose logging
uv run exo -v   # or -vv for more verbose

# Run tests (excludes slow tests by default)
uv run pytest

# Run all tests including slow tests
uv run pytest -m ""

# Run a specific test file
uv run pytest src/exo/shared/tests/test_election.py

# Run a specific test function
uv run pytest src/exo/shared/tests/test_election.py::test_function_name

# Type checking (strict mode)
uv run basedpyright

# Linting
uv run ruff check

# Format code (using nix)
nix fmt

Pre-Commit Checks (REQUIRED)

IMPORTANT: Always run these checks before committing code. CI will fail if these don't pass.

# 1. Type checking - MUST pass with 0 errors
uv run basedpyright

# 2. Linting - MUST pass
uv run ruff check

# 3. Formatting - MUST be applied
nix fmt

# 4. Tests - MUST pass
uv run pytest

Run all checks in sequence:

uv run basedpyright && uv run ruff check && nix fmt && uv run pytest

If nix fmt changes any files, stage them before committing. The CI runs nix flake check which verifies formatting, linting, and runs Rust tests.

Architecture

Node Composition

A single exo Node (src/exo/main.py) runs multiple components:

  • Router: libp2p-based pub/sub messaging via Rust bindings (exo_pyo3_bindings)
  • Worker: Handles inference tasks, downloads models, manages runner processes
  • Master: Coordinates cluster state, places model instances across nodes
  • Election: Bully algorithm for master election
  • API: FastAPI server for OpenAI-compatible chat completions

Message Flow

Components communicate via typed pub/sub topics (src/exo/routing/topics.py):

  • GLOBAL_EVENTS: Master broadcasts indexed events to all workers
  • LOCAL_EVENTS: Workers send events to master for indexing
  • COMMANDS: Workers/API send commands to master
  • ELECTION_MESSAGES: Election protocol messages
  • CONNECTION_MESSAGES: libp2p connection updates

Event Sourcing

The system uses event sourcing for state management:

  • State (src/exo/shared/types/state.py): Immutable state object
  • apply() (src/exo/shared/apply.py): Pure function that applies events to state
  • Master indexes events and broadcasts; workers apply indexed events

Key Type Hierarchy

  • src/exo/shared/types/: Pydantic models for all shared types
    • events.py: Event types (discriminated union)
    • commands.py: Command types
    • tasks.py: Task types for worker execution
    • state.py: Cluster state model

Rust Components

Rust code in rust/ provides:

  • networking: libp2p networking (gossipsub, peer discovery)
  • exo_pyo3_bindings: PyO3 bindings exposing Rust to Python
  • system_custodian: System-level operations

Dashboard

Svelte 5 + TypeScript frontend in dashboard/. Build output goes to dashboard/build/ and is served by the API.

Code Style Requirements

From .cursorrules:

  • Strict, exhaustive typing - never bypass the type-checker
  • Use Literal[...] for enum-like sets, typing.NewType for primitives
  • Pydantic models with frozen=True and strict=True
  • Pure functions with injectable effect handlers for side-effects
  • Descriptive names - no abbreviations or 3-letter acronyms
  • Catch exceptions only where you can handle them meaningfully
  • Use @final and immutability wherever applicable

Testing

Tests use pytest-asyncio with asyncio_mode = "auto". Tests are in tests/ subdirectories alongside the code they test. The EXO_TESTS=1 env var is set during tests.

Dashboard UI Testing & Screenshots

Building and Running the Dashboard

# Build the dashboard (must be done before running exo)
cd dashboard && npm install && npm run build && cd ..

# Start exo (serves the dashboard at http://localhost:52415)
uv run exo &
sleep 8  # Wait for server to start

Taking Headless Screenshots with Playwright

Use Playwright with headless Chromium for programmatic screenshots — no manual browser interaction needed.

Setup (one-time):

npx --yes playwright install chromium
cd /tmp && npm init -y && npm install playwright

Taking screenshots:

// Run from /tmp where playwright is installed: cd /tmp && node -e "..."
const { chromium } = require('playwright');
(async () => {
  const browser = await chromium.launch({ headless: true });
  const page = await browser.newPage({ viewport: { width: 1280, height: 800 } });
  await page.goto('http://localhost:52415', { waitUntil: 'networkidle' });
  await page.waitForTimeout(2000);

  // Inject test data into localStorage if needed (e.g., recent models)
  await page.evaluate(() => {
    localStorage.setItem('exo-recent-models', JSON.stringify([
      { modelId: 'mlx-community/Qwen3-30B-A3B-4bit', launchedAt: Date.now() },
    ]));
  });
  await page.reload({ waitUntil: 'networkidle' });
  await page.waitForTimeout(2000);

  // Interact with UI elements
  await page.locator('text=SELECT MODEL').click();
  await page.waitForTimeout(1000);

  // Take screenshot
  await page.screenshot({ path: '/tmp/screenshot.png', fullPage: false });
  await browser.close();
})();

Uploading Images to GitHub PRs

GitHub's API doesn't support direct image upload for PR comments. Workaround:

  1. Commit images to the branch (temporarily):

    cp /tmp/screenshot.png .
git add screenshot.png
git commit -m "temp: add screenshots for PR"
git push origin <branch>
COMMIT_SHA=$(git rev-parse HEAD)

  2. Post PR comment referencing the raw image URL (uses permanent commit SHA so images survive deletion):

    gh pr comment <PR_NUMBER> --body "![Screenshot](https://raw.githubusercontent.com/exo-explore/exo/${COMMIT_SHA}/screenshot.png)"

  3. Remove the images from the branch:

    git rm screenshot.png
git commit -m "chore: remove temporary screenshot files"
git push origin <branch>

    The images still render in the PR comment because they reference the permanent commit SHA.