tsunagi/AGENTS.md

AGENTS.md

Rules for anyone — human or automated — changing this repository. Read this before touching the code. Do not restate the full design here; follow the links.

What this project is

A proof-of-concept agent library for small private mesh networks. A user supplies a network name and one shared secret; agents derive the same network space independently, find each other, prove membership and exchange control messages. Scope and non-scope are in README.md.

There is no central server, no owner, no registration and no majority vote. Design accordingly: a majority is not a root of trust.

Architectural boundaries

Keep these separate. Crossing them is the main thing to review for.

• Control plane vs data plane. The separation is logical, not physical. The control protocol in src/proto/ knows nothing about packets, and src/dataplane/ knows nothing about the control protocol; either can be replaced on its own. Both may ride on iroh — refusing to would throw away iroh's NAT traversal and force the data plane to reimplement it. They use different ALPNs and different connections, so a busy or broken data plane cannot disturb control traffic.
• Plugins never learn reachability. An IpPlugin is handed a PacketLink per peer and moves datagrams over it. Addresses, hole punching and relays belong to src/dataplane/transport/. A plugin announcement says who, never where.
• The core never parses a plugin payload. See src/dataplane/mod.rs. Only src/dataplane/wireguard/announcement.rs interprets WireGuard payloads, and only after bounding every field. A data plane failure must never stop the control plane.
• Derived, not claimed. A peer's overlay address is derived from its public key. Outbound packets are routed to the owner of the destination address; inbound packets are dropped unless their source is the address derived for the peer that sent them. Never trust an address a peer announces.
• Signed state is the only durable agreement. A fact that must survive a participant being away goes in src/state/ as a record signed by its author, never in a session. Merging is deterministic, an older version never rolls back a newer one, and absence from a snapshot is not deletion. Never add a vote or a quorum: a majority is not a trust root here, and it would stall with one peer online.
• A record and the author's own version counter commit together, in one transaction, before the record is announced.
• Plugins own their system objects. A plugin creates and removes its own interface and nothing else. Never touch routing, DNS or firewall settings.
• Device identity vs network identity. The iroh endpoint id is the device's public key. NetworkId is derived from name + secret only. Never conflate them, and never let one change the other.
• Discovery vs authentication. Discovery returns unverified candidates. It never authenticates, never carries control messages and never mutates agent state. Membership is decided only by the handshake.
• Mandatory state vs disposable cache. state.sqlite is never silently reset: damage is a hard error. cache.sqlite may be deleted at any time and is recreated. A stale cache must never bypass identity or network authentication.
• Candidate vs observed address vs verified path. Report these as three different things. A missing value is None, never invented.

Rules that are not negotiable

1. Tests come first. Every substantial change ships with tests for the normal path and the important failures. See docs/testing.md. Do not add tests for getters or to move a coverage number.
2. Never change IDENTITY_SCHEME, the derivation labels, or the transcript encoding in src/identity/network.rs and src/proto/handshake.rs without treating it as an incompatible protocol change. Bumping the crate version or the control protocol version must not change an existing NetworkId.
3. Secrets never leak. Not into logs, not into Debug, not into status output, not into anything exported to the network. NetworkSecret and derived keys redact themselves and zeroize; keep it that way.
4. No panics on untrusted input. No unwrap, expect or panic on anything that came off the network. Clippy enforces this at warn level in the library; tests opt out explicitly at the top of each file.
5. Bounds before allocation. Frame lengths are checked against Limits::max_frame_len before a buffer is allocated. Every string, list and queue has a limit in src/config.rs.
6. Failure is contained. A bad signature, wrong secret, malformed packet or unknown version rejects one message or one session. It never stops another network and never stops the agent. There is no irreversible global error flag. A data plane failure must never stop the control plane.
7. The library owns no globals. No global tokio runtime, no global tracing subscriber, no signal handlers, no fork, no process::exit, no global mutable state. Several agents must run in one test process.
8. SQLite never blocks the executor. All database work goes through spawn_blocking. Never hold a transaction or a database lock across a network await. When signed records land, writing the record and bumping the author's own counter must be one transaction, committed before publishing to the network.
9. Shutdown is bounded. A peer that stops reading must not be able to hold up shutdown. Wind tasks down with a grace period and then abort.
10. Nothing from a remote announcement becomes a shell command, a filesystem path or an OS setting. The agent never touches interfaces or OS settings it did not create.

Where things live

path	responsibility
src/identity/	device identity; deterministic network space identity and derived keys
src/storage/	state.sqlite, cache.sqlite, directory ownership lock
src/discovery.rs	candidate sources; test and static backends
src/proto/	framing, message formats, membership handshake
src/net.rs	iroh endpoint adapter and observability snapshots
src/agent/	agent lifecycle, per-network runtimes, sessions, events, status
src/state/	signed records that outlive a session, their merge rules and address allocation
src/dataplane/	the plugin contract, the packet transport, and the WireGuard plugin
src/bin/tsunagi.rs	the command line agent; the only place that owns a runtime, a logger and signals
tests/	integration tests; tests/common/ is the shared harness

Add abstractions only at real substitution or testing boundaries. Do not add a trait per struct. Prefer one crate with clear modules over many small crates.

Testing rules

• Use real iroh endpoints on loopback, real handshakes, real SQLite in temporary directories, and independent agent instances.
• Discovery may be substituted. iroh, authentication, message passing and persistent storage may not be.
• No arbitrary multi-second sleep as the primary synchronisation. Wait for a specific event or condition under one overall deadline (wait_event, wait_until). settle() exists only for asserting that something did not happen.
• The default suite must pass with no internet, no DHT, no public relay, no administrator rights and no changes to OS network settings. Anything needing the internet or root stays out of the default set.
• The WireGuard packet interface may be substituted (MemoryTunFactory). Its key handling, announcements, derived addressing, the WireGuard protocol itself and address-ownership enforcement may not — the default suite runs real handshakes and real encryption.
• Running several library instances in one process is not a test of several system processes; do not describe it as one.

Before you open a change

cargo fmt --all -- --check
cargo clippy --locked --workspace --all-targets -- -D warnings
cargo test --locked --workspace --all-targets

CI runs these on Linux, macOS and Windows. A CI config existing is not evidence that tests ran on every OS — say what you actually ran.

Check the real API of the iroh version in Cargo.lock before using it. Do not invent methods from memory.