mDNS peer discovery broken when running from git source (uv sync + uv run)

[Sofille65]

Description

When running exo from a fresh git clone + uv sync (as opposed to the pre-built EXO.app), nodes on the same local network do not discover each other via mDNS. Each node starts, elects itself as Master, and runs in isolation — no peers are ever found.

The same machines running EXO.app v1.0.68 (pre-built DMG) form a 4-node cluster within seconds.

Environment

• Version: v1.0.68 (tag ba611f9c)
• Platform: macOS 26.3.1 (4x Mac Studio, Apple M3 Ultra, ARM64)
• Network: Same LAN (192.168.86.0/24), multicast working
• Python: 3.13.12 via uv 0.10.7
• exo_pyo3_bindings: 0.1.0, built from source with maturin

Steps to reproduce

1. git clone https://github.com/exo-explore/exo.git
2. cd exo && git checkout v1.0.68
3. cd dashboard && npm install && npm run build && cd ..
4. uv sync
5. uv run exo
6. Repeat on a second machine on the same LAN
7. Nodes never discover each other — each remains an isolated Master indefinitely

Investigation details

• Firewall: Disabled on all machines
• Multicast: Working — ping 224.0.0.251 gets responses from all machines on the LAN
• mDNS port: exo process correctly binds to UDP *:5353 (3 sockets confirmed via lsof)
• libp2p swarm: TCP LISTEN port is open (random high port)
• NETWORK_VERSION: Identical b"v0.0.1" on all nodes, no EXO_LIBP2P_NAMESPACE override
• Preshared key (pnet): Same source code = same SHA3 hash
• mDNS query interval: We patched MDNS_QUERY_INTERVAL from 1500s down to 5s in discovery.rs, force-rebuilt exo_pyo3_bindings, still no peers discovered after several minutes
• Connection updates: Zero ConnectionUpdate events — the Rust networking layer never reports any peer
• No errors: No error or warning in logs related to networking

Expected behavior

Nodes should discover each other via mDNS and form a cluster, as they do when running from the pre-built EXO.app.

Workaround

Use the pre-built EXO.app from GitHub releases instead of running from git source.

Hypothesis

The issue likely relates to how exo_pyo3_bindings is compiled via maturin during uv sync (dev/editable mode) vs how it is compiled and bundled in the PyInstaller-based EXO.app release. Possible causes:

• Different Rust feature flags or build profile (debug vs release)
• The maturin editable install may not correctly link or initialize the libp2p networking stack
• The tokio runtime spawned inside the Python process (via pyo3) may handle mDNS multicast sockets differently in dev mode

[AlexCheema]

That's surprising - this is working for me on a close to identical setup (all that's different is patch version of macOS 26.3).

Can you have a look in System Settings -> Privacy & Security -> Local Network
Do you have an entry for exo or python3.12 or Terminal.app there? Is it toggled on?