core+rendezvous: zero-config bootstrap + iroh on iOS

Two pieces that unblock the on-device cross-CGNAT test:

1. Rendezvous (new `rendezvous/` crate, tether-rendezvous, axum) — the only
   server tether still needs on iroh: maps room → {EndpointId}, in-memory, TTL,
   content-blind (room is a hash; never sees clipboard data). IrohTransport now
   registers under cfg.server and bootstraps gossip from the returned peers, and
   re-registers every 30s so late joiners can find it. The TETHER_IROH_BOOTSTRAP
   env var is demoted to a test override. Verified: two engines self-discover via
   a local rendezvous and sync text + a 200KB photo with zero env wiring.

2. iroh on Apple targets — the iroh-transport feature cross-compiles for
   ios-arm64 / ios-sim / macOS once IPHONEOS_DEPLOYMENT_TARGET=26.0 is set (ring/
   blake3 prebuilt objects target the newer SDK). build-apple.sh now exports the
   deployment targets and takes a TETHER_FEATURES switch;
   `TETHER_FEATURES=iroh-transport ./build-apple.sh` assembles + vendors the iroh
   xcframework (4891 iroh symbols in the iOS .a). Swift bindings are unchanged —
   the app builds on iroh with no Swift changes.

Remaining for the live test: deploy the rendezvous (+ optional self-hosted
iroh-relay) publicly on the homelab, then build TetherApp in Xcode and point its
server field at the rendezvous URL. Default ship build untouched throughout.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ARCHITECTURE.md

@@ -435,11 +435,23 @@ multi-modal payloads (text inline, audio/photo/data via `iroh-blobs`). Receiving
                   peers fetch P2P by hash and emit `MeshEvent::File`. Replaces the
                   M/C/E frame protocol. Verified: a 200 KB photo syncs A→B
                   E2E-decrypted alongside text (`iroh_engine` example).
-            - [ ] Remaining: rendezvous for zero-config bootstrap (today via
+            - [x] **Rendezvous for zero-config bootstrap** — `rendezvous/`
-                  `TETHER_IROH_BOOTSTRAP` env stopgap); cross-compile the feature
+                  (tether-rendezvous, axum): `room → {EndpointId}`, metadata-only,
-                  for iOS + build the xcframework with it; make webrtc/mdns/reqwest
+                  content-blind. IrohTransport registers under `cfg.server` and
-                  optional so the iroh/wasm build is lean; A/B vs RTC+LAN; flip the
+                  bootstraps gossip from the returned peers (env var now just a
-                  feature on by default.
+                  test override). Verified: two engines self-discover via a local
+                  rendezvous, sync text + photo, zero env wiring.
+            - [x] **iOS/Apple cross-compile + xcframework** — `iroh-transport`
+                  builds for ios-arm64 / ios-sim / macOS (needs
+                  `IPHONEOS_DEPLOYMENT_TARGET=26.0`, now in `build-apple.sh` along
+                  with a `TETHER_FEATURES` switch). `TETHER_FEATURES=iroh-transport
+                  ./build-apple.sh` assembles + vendors the iroh xcframework
+                  (4,891 iroh symbols in the iOS staticlib); Swift bindings
+                  unchanged, so the app builds with no Swift changes.
+            - [ ] Remaining: deploy the rendezvous + a self-hosted iroh-relay
+                  publicly (homelab) for the on-device cross-CGNAT test; make
+                  webrtc/mdns/reqwest optional for a lean iroh/wasm build; A/B vs
+                  RTC+LAN; flip the feature on by default.
 - [ ] Spike **Automerge** as the Sync tier; re-express the clipboard as a tiny
       app over replicated state to validate the App API.
 - [ ] Durable device keypairs + authenticated handshake (Noise/`snow`, or

core/build-apple.sh

@@ -13,11 +13,25 @@ IOS=aarch64-apple-ios
 SIM=aarch64-apple-ios-sim
 MAC=aarch64-apple-darwin
 
+# Deployment targets — must match the apps (iOS 26). Without this the linker
+# defaults to iOS 10 and the cdylib fails to link against ring/blake3's prebuilt
+# assembly objects (built for the newer SDK).
+export IPHONEOS_DEPLOYMENT_TARGET=26.0
+export MACOSX_DEPLOYMENT_TARGET=26.0
+
+# Optional Cargo features, e.g. TETHER_FEATURES=iroh-transport to build the
+# iroh-backed core. Empty → the default (legacy SSE/RTC/LAN) build. Plain string
+# (not an array) so macOS bash 3.2 + `set -u` doesn't choke when it's empty.
+FEATURES="${TETHER_FEATURES:-}"
+FEAT_ARGS=""
+[ -n "$FEATURES" ] && FEAT_ARGS="--features $FEATURES" && echo "▸ features: $FEATURES"
+
 echo "▸ building static libs ($IOS, $SIM, $MAC)…"
 rustup target add "$IOS" "$SIM" "$MAC" >/dev/null 2>&1 || true
-cargo build --release --target "$IOS" --lib
+# shellcheck disable=SC2086  # intentional word-split of FEAT_ARGS
-cargo build --release --target "$SIM" --lib
+cargo build --release --target "$IOS" --lib $FEAT_ARGS
-cargo build --release --target "$MAC" --lib
+cargo build --release --target "$SIM" --lib $FEAT_ARGS
+cargo build --release --target "$MAC" --lib $FEAT_ARGS
 
 echo "▸ generating Swift bindings…"
 cargo run --release --bin uniffi-bindgen -- \

core/examples/iroh_engine.rs

@@ -11,7 +11,7 @@
 //! it to B.
 
 use std::sync::mpsc;
-use std::time::{Duration, Instant};
+use std::time::Duration;
 
 use tethercore::{Engine, Message, MessageHandler};
 
@@ -39,40 +39,26 @@ impl MessageHandler for Collector {
 fn main() {
     let account = "pecord@gmail.com"; // same account → same room → same topic + key
     let room = "iroh-engine-test";
-    let server = "unused"; // iroh ignores cfg.server; it uses n0 infra
+    // Zero-config bootstrap via the rendezvous (run tether-rendezvous first, or
+    // point at a deployed one). Both engines register under `room` and discover
+    // each other — no env var, no manual id wiring.
+    let server = std::env::var("TETHER_RENDEZVOUS")
+        .unwrap_or_else(|_| "http://localhost:8765".into());
+    eprintln!("rendezvous: {server}");
 
-    // Opener (no bootstrap yet).
     let a = Engine::new(
-        server.into(), room.into(), "iroh-a".into(), "macos".into(), "A".into(), account.into(),
+        server.clone(), room.into(), "iroh-a".into(), "macos".into(), "A".into(), account.into(),
     );
     a.start(Box::new(Noop));
 
-    // Wait for A's iroh endpoint to come online, then bootstrap B off it.
-    let a_id = {
-        let deadline = Instant::now() + Duration::from_secs(20);
-        loop {
-            if let Some(id) = a.iroh_id() {
-                break id;
-            }
-            if Instant::now() > deadline {
-                eprintln!("❌ A never came online");
-                std::process::exit(1);
-            }
-            std::thread::sleep(Duration::from_millis(200));
-        }
-    };
-    eprintln!("A online, id={a_id}");
-    std::env::set_var("TETHER_IROH_BOOTSTRAP", &a_id);
-
-    // Joiner (bootstraps to A via the env var its IrohTransport reads at start).
     let (tx, rx) = mpsc::channel();
     let (ftx, frx) = mpsc::channel();
     let b = Engine::new(
-        server.into(), room.into(), "iroh-b".into(), "ios".into(), "B".into(), account.into(),
+        server.clone(), room.into(), "iroh-b".into(), "ios".into(), "B".into(), account.into(),
     );
     b.start(Box::new(Collector { text: tx, file: ftx }));
 
-    eprintln!("waiting for gossip topic to form…");
+    eprintln!("waiting for gossip topic to form (via rendezvous)…");
     std::thread::sleep(Duration::from_secs(8));
 
     // 1) Text clipboard over gossip.

core/src/iroh.rs

@@ -77,7 +77,8 @@ fn topic_for(room: &str) -> TopicId {
     TopicId::from_bytes(id)
 }
 
-fn bootstrap_ids() -> Vec<EndpointId> {
+/// Env-var bootstrap (test/override path): comma-separated EndpointIds.
+fn env_bootstrap_ids() -> Vec<EndpointId> {
     std::env::var("TETHER_IROH_BOOTSTRAP")
         .ok()
         .into_iter()
@@ -89,6 +90,32 @@ fn bootstrap_ids() -> Vec<EndpointId> {
         .collect()
 }
 
+/// Register this node with the rendezvous (cfg.server) under our room and get
+/// back the current peers to bootstrap the gossip topic. Zero-config: the room
+/// is a hash, content never touches the rendezvous. No-op if server isn't a URL.
+async fn rendezvous_register(server: &str, room: &str, my_id: &str) -> Vec<EndpointId> {
+    if !(server.starts_with("http://") || server.starts_with("https://")) {
+        return Vec::new();
+    }
+    let url = format!("{}/rendezvous/register", server.trim_end_matches('/'));
+    let body = serde_json::json!({ "room": room, "id": my_id });
+    let resp = match reqwest::Client::new().post(&url).json(&body).send().await {
+        Ok(r) => r,
+        Err(_) => return Vec::new(),
+    };
+    let Ok(v) = resp.json::<serde_json::Value>().await else {
+        return Vec::new();
+    };
+    v["peers"]
+        .as_array()
+        .map(|a| {
+            a.iter()
+                .filter_map(|p| p.as_str()?.parse::<EndpointId>().ok())
+                .collect()
+        })
+        .unwrap_or_default()
+}
+
 impl IrohTransport {
     /// Fetch a blob announced over gossip from its provider and surface it.
     async fn fetch_blob(blobs: Blobs, events: EventTx, ann: BlobAnnounce) {
@@ -154,8 +181,28 @@ impl Transport for IrohTransport {
                 my_id: my_id.clone(),
             });
 
+            // Bootstrap: env override (tests) + the rendezvous (zero-config).
+            let mut boot = env_bootstrap_ids();
+            boot.extend(rendezvous_register(&this.cfg.server, &this.cfg.room, &my_id).await);
+            eprintln!("tethercore[iroh]: bootstrapping with {} peer(s)", boot.len());
+
+            // Keep re-registering so late-joining devices can bootstrap off us
+            // (rendezvous TTL is 90s; refresh well under it).
+            {
+                let server = this.cfg.server.clone();
+                let room = this.cfg.room.clone();
+                let id = my_id.clone();
+                let running = running.clone();
+                tokio::spawn(async move {
+                    while running.load(Ordering::SeqCst) {
+                        tokio::time::sleep(std::time::Duration::from_secs(30)).await;
+                        let _ = rendezvous_register(&server, &room, &id).await;
+                    }
+                });
+            }
+
             let topic = topic_for(&this.cfg.room);
-            let sub = match gossip.subscribe_and_join(topic, bootstrap_ids()).await {
+            let sub = match gossip.subscribe_and_join(topic, boot).await {
                 Ok(s) => s,
                 Err(e) => {
                     eprintln!("tethercore[iroh]: topic join failed: {e}");

rendezvous/.gitignore

@@ -0,0 +1 @@
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rendezvous/Cargo.lock

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rendezvous/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "tether-rendezvous"
+version = "0.1.0"
+edition = "2021"
+description = "Tiny bootstrap rendezvous for tether's iroh gossip: room → {EndpointId}. Metadata-only, content never touches it. The one thing the supernode does for zero-config discovery."
+
+[[bin]]
+name = "tether-rendezvous"
+path = "src/main.rs"
+
+[dependencies]
+axum = "0.7"
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "net", "time", "signal"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"

rendezvous/README.md

@@ -0,0 +1,77 @@
+# tether-rendezvous
+
+The one piece of server tether still needs once it's on iroh: a **bootstrap
+rendezvous**. To join the gossip topic a device needs to reach ≥1 peer already
+in it; this hands it one. After that, everything is peer-to-peer.
+
+It is deliberately tiny and **content-blind**:
+- maps `room → {EndpointId: last_seen}` in memory, TTL 90s
+- `room` is already `sha256(account)[..4]`, so the account is never exposed
+- it only ever sees iroh public keys + timestamps — **never clipboard content**
+  (that's E2E between peers)
+
+This is "supernode #1, the boring half." The other half is a self-hosted
+`iroh-relay` (for holepunch-assist / relay fallback). Neither replaces the old
+Go server's role in *content* — there is none anymore.
+
+## API
+
+```
+POST /rendezvous/register  {"room":"<hex>","id":"<endpoint-id>"}
+     → {"peers":["<other-id>", ...]}      # current members minus the caller
+GET  /rendezvous/peers?room=<hex>          → {"peers":[...]}
+GET  /healthz                              → "ok"
+```
+
+Clients register on a short interval (well under the 90s TTL) so the member list
+reflects who's actually online.
+
+## Run
+
+```
+cargo run --release            # binds 0.0.0.0:8765
+PORT=9000 cargo run --release
+```
+
+## Deploy (homelab)
+
+It needs to be **publicly reachable** for cross-network (cellular/CGNAT) devices
+to bootstrap — same requirement as the iroh-relay. On the homelab:
+
+1. Run it on a CT/VM (systemd unit below).
+2. Front it with Caddy for TLS, e.g. `rendezvous.pecord.io`:
+
+   ```
+   rendezvous.pecord.io {
+       reverse_proxy 127.0.0.1:8765
+   }
+   ```
+
+   (Plain HTTP reverse-proxy is fine — unlike the iroh-relay, there's no
+   UDP/QUIC path here, just small JSON over HTTPS.)
+
+3. Point the tether clients' server field at `https://rendezvous.pecord.io`.
+
+### systemd unit
+
+```ini
+[Unit]
+Description=tether rendezvous
+After=network-online.target
+
+[Service]
+ExecStart=/opt/tether/tether-rendezvous
+Environment=PORT=8765
+Restart=always
+RestartSec=2
+
+[Install]
+WantedBy=multi-user.target
+```
+
+## Security note
+
+Registration is unauthenticated — anyone who knows a `room` (a hash) can register
+an id or enumerate members. That's metadata only and content stays E2E, but a
+production deployment should add a token/auth gate and rate-limiting (the
+`MAX_PER_ROOM` cap is only a flood blunt). Tracked as a follow-up.

rendezvous/src/main.rs

@@ -0,0 +1,104 @@
+//! tether-rendezvous — the only thing the server still does once tether is on
+//! iroh: hand a joining device one current peer so it can bootstrap into the
+//! gossip topic. After that, everything is peer-to-peer.
+//!
+//! It maps `room → {EndpointId: last_seen}`, in memory, with a short TTL. The
+//! room is already sha256(account)[..4], so the account is never exposed; and it
+//! only ever sees iroh public keys + timestamps — **never content** (that's E2E
+//! between peers). This is "supernode #1, the boring part"; the iroh-relay is
+//! the other part.
+//!
+//! Run:  tether-rendezvous           # binds 0.0.0.0:8765
+//!       PORT=9000 tether-rendezvous
+//! Behind Caddy at e.g. rendezvous.pecord.io. Clients point cfg.server at it.
+//!
+//! API:
+//!   POST /rendezvous/register  {"room": "...", "id": "<endpoint-id>"}
+//!        → {"peers": ["<other-id>", ...]}     (current members minus the caller)
+//!   GET  /rendezvous/peers?room=...           → {"peers": [...]}
+//!   GET  /healthz                             → "ok"
+
+use std::collections::HashMap;
+use std::sync::{Arc, Mutex};
+use std::time::{Duration, Instant};
+
+use axum::{
+    extract::{Query, State},
+    routing::{get, post},
+    Json, Router,
+};
+use serde::{Deserialize, Serialize};
+
+/// Members are forgotten this long after their last register — so a member list
+/// reflects who's actually online (clients re-register on a shorter interval).
+const TTL: Duration = Duration::from_secs(90);
+/// Cap members per room to blunt a junk-registration flood.
+const MAX_PER_ROOM: usize = 64;
+
+type Rooms = Arc<Mutex<HashMap<String, HashMap<String, Instant>>>>;
+
+#[derive(Deserialize)]
+struct Register {
+    room: String,
+    id: String,
+}
+
+#[derive(Deserialize)]
+struct PeersQuery {
+    room: String,
+}
+
+#[derive(Serialize)]
+struct Peers {
+    peers: Vec<String>,
+}
+
+fn live_peers(rooms: &Rooms, room: &str, exclude: Option<&str>) -> Vec<String> {
+    let now = Instant::now();
+    let mut map = rooms.lock().unwrap();
+    let members = map.entry(room.to_string()).or_default();
+    members.retain(|_, seen| now.duration_since(*seen) < TTL);
+    members
+        .keys()
+        .filter(|id| Some(id.as_str()) != exclude)
+        .cloned()
+        .collect()
+}
+
+async fn register(State(rooms): State<Rooms>, Json(r): Json<Register>) -> Json<Peers> {
+    if !r.room.is_empty() && !r.id.is_empty() {
+        let now = Instant::now();
+        let mut map = rooms.lock().unwrap();
+        let members = map.entry(r.room.clone()).or_default();
+        members.retain(|_, seen| now.duration_since(*seen) < TTL);
+        if members.len() < MAX_PER_ROOM || members.contains_key(&r.id) {
+            members.insert(r.id.clone(), now);
+        }
+    }
+    Json(Peers { peers: live_peers(&rooms, &r.room, Some(&r.id)) })
+}
+
+async fn peers(State(rooms): State<Rooms>, Query(q): Query<PeersQuery>) -> Json<Peers> {
+    Json(Peers { peers: live_peers(&rooms, &q.room, None) })
+}
+
+#[tokio::main]
+async fn main() {
+    let port: u16 = std::env::var("PORT").ok().and_then(|p| p.parse().ok()).unwrap_or(8765);
+    let rooms: Rooms = Arc::new(Mutex::new(HashMap::new()));
+
+    let app = Router::new()
+        .route("/rendezvous/register", post(register))
+        .route("/rendezvous/peers", get(peers))
+        .route("/healthz", get(|| async { "ok" }))
+        .with_state(rooms);
+
+    let listener = tokio::net::TcpListener::bind(("0.0.0.0", port)).await.unwrap();
+    println!("tether-rendezvous listening on 0.0.0.0:{port}");
+    axum::serve(listener, app)
+        .with_graceful_shutdown(async {
+            let _ = tokio::signal::ctrl_c().await;
+        })
+        .await
+        .unwrap();
+}