Dev Desktop Sandbox

Desktop (Electron) sandbox instances

make dev + make start (Electron) uses MUX_ROOT for persisted state (config, sessions, worktrees, etc.). Running multiple Electron instances against the same mux root is noisy and risky during development.

This skill documents the repo workflow for starting multiple desktop dev instances in parallel (including from different git worktrees) by giving each instance its own temporary MUX_ROOT.

Quick start

make dev-desktop-sandbox

What it does

• Creates a fresh temporary MUX_ROOT directory
• Copies these files into the sandbox if present:
  • providers.jsonc (provider config)
  • config.json (project list)
• Picks free ports:
  • Vite devserver port (used by the renderer)
  • Electron remote debugging port (optional)
• Runs make dev with:
  • MUX_ROOT=<temp>
  • MUX_VITE_PORT=<free-port>
• Waits for Vite to be reachable, then runs make build-static (Electron expects dist/splash.html)
• Launches Electron (bunx electron .) with:
  • MUX_ROOT=<temp>
  • MUX_DEVSERVER_HOST=127.0.0.1
  • MUX_DEVSERVER_PORT=<vite-port>
  • MUX_SERVER_PORT=0 by default (avoids EADDRINUSE if your config.json pins apiServerPort)
  • CMUX_ALLOW_MULTIPLE_INSTANCES=1 (so you can run alongside another dev instance)

Options

# Use a specific root to seed from (defaults to $MUX_ROOT then ~/.mux-dev then ~/.mux)
SEED_MUX_ROOT=~/.mux-dev make dev-desktop-sandbox

# Keep the sandbox root directory after exit (useful for debugging)
KEEP_SANDBOX=1 make dev-desktop-sandbox

# Pin Vite port
VITE_PORT=5174 make dev-desktop-sandbox

# Control how long we wait for Vite to come up (ms)
VITE_READY_TIMEOUT_MS=120000 make dev-desktop-sandbox

# Enable/pin Electron remote debugging port (defaults to an auto-picked free port)
ELECTRON_DEBUG_PORT=9223 make dev-desktop-sandbox

# Disable Electron remote debugging entirely
ELECTRON_DEBUG_PORT=0 make dev-desktop-sandbox

# Override the internal API server port (defaults to 0/random for sandboxes)
MUX_SERVER_PORT=3772 make dev-desktop-sandbox

# Override which make binary to use
MAKE=gmake make dev-desktop-sandbox

Optional: deeper Electron isolation (MUX_E2E=1)

Even with a unique MUX_ROOT, Electron's userData directory (localStorage, window state, single-instance lock, etc.) is not automatically relocated unless MUX_E2E=1 is set.

If you want full isolation (including userData), run:

MUX_E2E=1 make dev-desktop-sandbox

Security notes

• providers.jsonc may contain API keys.
• The sandbox root directory is created on disk (usually under your system temp dir).
• This flow intentionally does not copy secrets.json.