feat: auto-detect connection — fall back to direct USB serial when mux is unavailable

- Enable clippy pedantic + nursery lints; fix all warnings
- Add config validation (SF, CR, frequency range checks)
- Zeroize passphrase intermediates after key derivation
- Convert to lib+bin crate for fuzz target accessibility
- Replace Vec with VecDeque for O(1) log/bucket rotation
- Add TUI minimum terminal size guard

Testing:
- 145 unit + property tests (was 15)
- 6 proptest groups (frame roundtrip, hash, SNR, air time, peer list, padding)
- 2 cargo-fuzz targets (gossip frame decode, peer list decode)
- cargo-mutants: 0 missed, 241 caught, 54 unviable

Documentation:
- README with prerequisites, quick start, config reference, architecture
- Module-level and item-level rustdoc on all public items
- LICENSE (MIT), rustfmt.toml, .gitignore

Infrastructure:
- GitHub Actions CI (fmt, clippy, test, audit)
- cargo-mutants config (.cargo/mutants.toml)
- justfile for common tasks

.cargo/mutants.toml

@@ -0,0 +1,55 @@
+# cargo-mutants configuration
+# Run with: cargo mutants
+# Install with: cargo install cargo-mutants
+
+# Exclude entire files that are untestable (main requires full app, setup requires interactive stdin)
+exclude_globs = [
+    "src/main.rs",
+    "src/setup.rs",
+]
+
+# Exclude specific functions that require hardware, network, terminal, or full async infrastructure
+exclude_re = [
+    # Equivalent mutants: Instant arithmetic never produces exact equality,
+    # so `< ttl` and `<= ttl` behave identically in practice.
+    "replace < with <= in DedupCache",
+    "replace < with <= in decode_peer_list",
+    # rate_limit.rs: equivalent mutant (secs is always > 0 from lora_air_time)
+    "replace > with >= in RateLimiter::from_radio_config",
+    # radio.rs: hardware-dependent functions
+    "radio_loop",
+    "connect_and_run",
+    # gossip.rs: async network functions
+    "Gossip::new",
+    "Gossip::shutdown",
+    "spawn_accept_loop",
+    "handle_incoming",
+    "spawn_receiver",
+    "spawn_broadcaster",
+    "spawn_dht_heartbeat",
+    "dht_read_and_join",
+    "dht_publish",
+    "dht_get_peers",
+    # router.rs: async event loop
+    "^src/router\\.rs:.* replace run ",
+    "^src/router\\.rs:.* in run$",
+    # tui.rs: terminal rendering functions
+    "tui::run",
+    "tui_loop",
+    "restore_terminal",
+    "draw_ui",
+    "draw_header",
+    "draw_network",
+    "draw_radio",
+    "draw_stats",
+    "draw_log",
+    "draw_activity",
+    "draw_sparkline_section",
+    "draw_shutdown_overlay",
+    "panel_block",
+    "status_pill",
+    "kv_line",
+]
+
+# Timeout per mutant test (seconds)
+timeout_multiplier = 3.0

.github/workflows/ci.yml

@@ -0,0 +1,44 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Clone donglora (sibling dependency)
+        uses: actions/checkout@v4
+        with:
+          repository: swaits/donglora
+          path: ../donglora
+
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: "1.94.1"
+          components: rustfmt, clippy
+
+      - uses: Swatinem/rust-cache@v2
+
+      - name: Format check
+        run: cargo fmt --check
+
+      - name: Clippy
+        run: cargo clippy --all-targets -- -D warnings
+
+      - name: Test
+        run: cargo test
+
+      - name: Install cargo-deny
+        run: cargo install cargo-deny --locked
+
+      - name: Audit (advisories + licenses)
+        run: cargo deny check

.gitignore

@@ -1 +1,11 @@
 /target
+/fuzz/target
+/fuzz/corpus
+/fuzz/Cargo.lock
+/mutants.out
+/mutants.out.old
+.jj/
+*.swp
+*.swo
+*~
+.DS_Store

CHANGELOG.md

@@ -0,0 +1,21 @@
+# Changelog
+
+## [0.2.0] - 2026-04-06
+
+### Added
+
+- Auto-detect connection mode: when no `port` is configured, the bridge now
+  tries the mux daemon first and falls back to direct USB serial
+  (`find_port()`) if the mux is unavailable. Previously it would retry the mux
+  forever.
+
+### Changed
+
+- Config negotiation on direct serial connections now pushes `SetConfig` with
+  the desired radio config when it differs from the dongle's current config.
+  On mux connections, the existing behavior (accept the mux's config) is
+  unchanged.
+
+## [0.1.0] - 2026-04-06
+
+Initial release.

Cargo.toml

@@ -1,32 +1,54 @@
 [package]
 name = "donglora-bridge"
-version = "0.1.0"
+version = "0.2.0"
 edition = "2024"
 authors = ["Stephen Waits <steve@waits.net>"]
 license = "MIT"
 description = "Peer-to-peer LoRa bridge using iroh and DongLoRa"
+repository = "https://github.com/swaits/donglora-bridge"
+homepage = "https://github.com/swaits/donglora-bridge"
+keywords = ["lora", "bridge", "gossip", "p2p", "iot"]
+categories = ["network-programming", "command-line-utilities"]
+readme = "README.md"
+rust-version = "1.94.1"
+exclude = [".jj/", ".github/"]
 
 [dependencies]
-donglora-client = { path = "../donglora/clients/rust" }
+donglora-client = "0.1"
 iroh = "0.97"
+iroh-gossip = "0.97"
+mainline = { version = "6", features = ["async"] }
 tokio = { version = "1", features = ["full"] }
 clap = { version = "4", features = ["derive"] }
 serde = { version = "1", features = ["derive"] }
-toml = "0.8"
+toml = "1"
 blake3 = "1"
-ratatui = "0.29"
+ratatui = "0.30"
-crossterm = "0.28"
+crossterm = "0.29"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 tracing-appender = "0.2"
 anyhow = "1"
 dirs = "6"
 bytes = "1"
+futures-lite = "2"
 rand = "0.9"
 hex = "0.4.3"
+sha2 = "0.10"
 tokio-util = { version = "0.7.18", features = ["rt"] }
+jiff = "0.2.23"
+zeroize = "1"
+
+[dev-dependencies]
+proptest = "1"
+tempfile = "3"
 
 [lints.clippy]
+pedantic = { level = "warn", priority = -1 }
+nursery = { level = "warn", priority = -1 }
 unwrap_used = "deny"
 expect_used = "deny"
 panic = "deny"
+similar_names = "allow"
+module_name_repetitions = "allow"
+missing_errors_doc = "allow"

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2025 Stephen Waits <steve@waits.net>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -0,0 +1,290 @@
+# donglora-bridge
+
+[![CI](https://github.com/swaits/donglora-bridge/actions/workflows/ci.yml/badge.svg)](https://github.com/swaits/donglora-bridge/actions/workflows/ci.yml)
+[![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](LICENSE)
+![Rust](https://img.shields.io/badge/rust-1.94.1%2B-orange)
+
+**donglora-bridge** connects LoRa radios to the internet so packets heard by one
+radio can be retransmitted by another radio anywhere in the world.
+
+[LoRa](https://en.wikipedia.org/wiki/LoRa) is a long-range, low-power wireless
+protocol used by off-grid mesh networks like
+[MeshCore](https://github.com/rocketgithub/meshcore-firmware). A single LoRa
+radio might cover a few kilometers. This bridge removes that limit: any packet
+your radio hears gets relayed over the internet to every other bridge running the
+same passphrase, and their radios retransmit it locally. The result is a single
+mesh network across a larger geographic area.
+
+There is no central server. Bridges discover each other automatically using the
+[Mainline DHT](https://en.wikipedia.org/wiki/Mainline_DHT) and communicate
+through an encrypted peer-to-peer gossip swarm.
+
+![TUI Screenshot](screenshot.png)
+
+## What you need
+
+### 1. A DongLoRa radio
+
+[DongLoRa](https://github.com/swaits/donglora) is open-source firmware that
+turns a supported LoRa development board (such as a Heltec WiFi LoRa 32 or
+similar ESP32+SX1262 board) into a USB LoRa dongle. You will need to:
+
+1. **Get a board** -- any ESP32 board with an SX1262 LoRa radio that DongLoRa
+   supports. See the [DongLoRa README](https://github.com/swaits/donglora) for
+   the full list.
+2. **Flash the DongLoRa firmware** onto the board. Instructions are in the
+   DongLoRa repository.
+3. **Plug it in via USB**. The board appears as a serial device
+   (e.g. `/dev/ttyACM0` on Linux).
+
+### 2. (Optional) donglora-mux
+
+The bridge works fine without the mux -- it connects directly to the USB device.
+The mux is only needed if you want multiple programs to share a single DongLoRa
+radio at the same time (e.g. running two bridges with different configs, or a
+bridge alongside another donglora-client program).
+
+```sh
+cargo install donglora-mux
+```
+
+Run `donglora-mux` before starting the bridge. The bridge auto-detects the mux
+when it's running and falls back to direct USB serial when it's not.
+
+### 3. donglora-bridge (this project)
+
+Install via cargo:
+
+```sh
+cargo install donglora-bridge
+```
+
+Or via [mise](https://mise.jdx.dev/):
+
+```sh
+mise use -g cargo:donglora-bridge
+```
+
+Or build from source:
+
+```sh
+git clone https://github.com/swaits/donglora-bridge.git
+cd donglora-bridge
+cargo build --release
+```
+
+Requires Linux. macOS may work but is untested.
+
+## Quick start
+
+### 1. Plug in your DongLoRa board and (optionally) start the mux
+
+```sh
+donglora-mux          # optional -- skip if not sharing the radio
+```
+
+### 2. Run the bridge
+
+```sh
+donglora-bridge
+```
+
+On first run, an interactive wizard walks you through configuration:
+
+- **Passphrase** (required) -- every bridge using the same passphrase joins the
+  same network. Pick something unique to your group.
+- **Radio settings** -- frequency, bandwidth, spreading factor, etc. The
+  defaults match MeshCore US/Canada recommended values. If you're bridging a
+  MeshCore network, just press Enter through these.
+
+The config is saved to `~/.config/donglora-bridge/config.toml`. To change it
+later, run `donglora-bridge config`.
+
+### 3. That's it
+
+The TUI shows real-time stats. On another machine (or continent), repeat the
+same steps with the same passphrase. The two bridges will discover each other
+via DHT and start relaying packets within seconds.
+
+```sh
+donglora-bridge                    # TUI mode (default)
+donglora-bridge --log-only         # headless mode (structured logs to stdout)
+donglora-bridge --config path.toml # custom config file
+donglora-bridge config             # re-run setup wizard
+```
+
+### Running multiple bridges
+
+To run more than one bridge on the same machine (e.g. bridging two separate
+MeshCore networks), create a config file per bridge and run each with
+`--config`:
+
+```sh
+donglora-bridge --config ~/bridge-network-a.toml
+donglora-bridge --config ~/bridge-network-b.toml
+```
+
+Each config can specify a different passphrase, different radio settings, and
+(if using the mux) share the same radio. Without the mux, each bridge needs its
+own USB dongle and an explicit `port` in its config to avoid both trying to open
+the same device.
+
+## Features
+
+- **Gossip swarm** -- broadcast packets via [iroh-gossip](https://github.com/n0-computer/iroh), a QUIC-based overlay network
+- **Zero-config peer discovery** -- automatic bootstrapping via BitTorrent mainline DHT ([BEP44](http://bittorrent.org/beps/bep_0044.html) mutable items)
+- **Content-hash deduplication** -- blake3 hashing suppresses duplicate packets across all bridges
+- **Air-time-aware rate limiting** -- token bucket calculated from LoRa radio parameters (Semtech LoRa time-on-air formula)
+- **Real-time terminal UI** -- network status, radio config, packet log, activity sparklines
+- **Resilient radio connection** -- exponential backoff reconnection with liveness pings
+- **Headless mode** -- structured logs to stdout for servers (`--log-only`)
+- **Interactive setup wizard** -- guided first-run configuration
+- **Shared passphrase security** -- all cryptographic keys derived deterministically from a single passphrase
+
+## TUI overview
+
+| Panel | Content |
+|-------|---------|
+| **Network** | Topic ID, peer count, DHT status, last publish time |
+| **Radio** | Device, frequency, bandwidth, SF, CR, sync word, TX power, preamble, CAD |
+| **Stats** | Uptime, RF/Net RX/TX, dedup hits, rate limit drops, queue drops |
+| **Packet Log** | Scrolling log: age, hash, RF/Net direction, size, RSSI, SNR, action |
+| **Activity** | Sparkline charts: RX rate, TX rate, average SNR (1-second buckets, 5-minute window) |
+
+Press `q` or `Ctrl+C` to shut down gracefully.
+
+## Configuration
+
+Default location: `~/.config/donglora-bridge/config.toml`
+
+```toml
+[radio]
+# port = "/dev/ttyACM0"   # serial port (omit for auto-detect: tries mux, then USB)
+frequency = 910525000      # Hz (default: 910.525 MHz)
+bandwidth = "62.5kHz"      # 7.8kHz, 10.4kHz, 15.6kHz, 20.8kHz, 31.25kHz,
+                           # 41.7kHz, 62.5kHz, 125kHz, 250kHz, 500kHz
+spreading_factor = 7       # 7-12
+coding_rate = 5            # 5-8 (meaning 4/5 to 4/8)
+sync_word = 0x3444         # hex, 2 bytes
+tx_power = "22"            # dBm integer or "max"
+preamble = 16              # symbols
+cad = true                 # channel activity detection
+
+[bridge]
+passphrase = "your-shared-secret"  # REQUIRED: all bridges with same passphrase join the same swarm
+dedup_window_secs = 300            # duplicate suppression window (default: 5 minutes)
+tx_queue_size = 32                 # max pending radio TX packets
+# rate_limit_pps = 5.0            # optional: override calculated TX rate (packets/sec)
+# log_file = "/path/to/bridge.log"  # optional: override log path
+```
+
+Default radio settings match MeshCore US/Canada recommended parameters.
+
+## How it works
+
+### Passphrase key derivation
+
+A single passphrase deterministically derives three values:
+
+1. **Topic ID** -- `blake3(APP_PREFIX + passphrase)` -- identifies the gossip swarm
+2. **DHT signing key** -- ed25519 from `SHA-256(APP_PREFIX + "sign:" + passphrase)` -- authenticates DHT records
+3. **DHT salt** -- first 20 bytes of `SHA-256(APP_PREFIX + "salt:" + passphrase)` -- namespaces the DHT key
+
+All nodes with the same passphrase compute identical keys and automatically join
+the same network.
+
+### Gossip swarm
+
+Each bridge creates an ephemeral iroh endpoint (fresh ed25519 identity per
+launch) and subscribes to the derived topic. Radio packets are wrapped in a
+`GossipFrame` (32-byte sender ID + RSSI + SNR + payload) and broadcast to all
+neighbors. Received frames are decoded and queued for radio transmission.
+
+### DHT peer discovery
+
+Peers find each other through BitTorrent's mainline DHT using BEP44 mutable
+items. Peer lists are encoded as `[count:u16 LE][id:32B]...` (max 27 peers per
+record to stay under the 1000-byte value limit).
+
+**When alone** (no neighbors): reads DHT every 3 seconds, merge-publishes every
+30 seconds (preserves existing peers, never destructive).
+
+**When connected**: relaxed 5-minute heartbeat with random jitter. Publishes
+self + live neighbors only (purges stale peers).
+
+**On shutdown**: publishes neighbors without self, so other nodes can still
+bootstrap from live peers.
+
+### Deduplication
+
+Every packet payload is hashed with blake3 (32 bytes). A time-bounded cache
+(default 300s, pruned every 30s) suppresses duplicates from both radio and
+gossip directions.
+
+### Rate limiting
+
+A token bucket rate limiter prevents radio channel saturation. The rate is
+calculated from the LoRa air time formula (Semtech SX1276):
+
+```
+air_time = preamble_time + payload_symbol_count * symbol_time
+rate = 0.5 / air_time  (50% duty cycle target)
+```
+
+Default burst allowance is 3 packets. The rate can be manually overridden with
+`rate_limit_pps` in the config.
+
+### Radio communication
+
+A dedicated blocking thread communicates with the DongLoRa hardware via
+`donglora-client`. Features:
+
+- **Config negotiation**: reads existing config first; only sets if needed
+- **Exponential backoff reconnection**: 250ms to 5s, resets after 5s of uptime
+- **Liveness pings**: every 2s of idle, detects silently-dead connections
+- **SNR filtering**: drops packets below the demodulation floor
+
+### Architecture
+
+```
+                        ┌─────────────────────────────────────┐
+                        │           donglora-bridge           │
+                        │                                     │
+  DongLoRa    ┌────────┐│  ┌────────┐   ┌──────┐   ┌───────┐  │    Internet
+  USB dongle◄─┤ Radio  ├┤◄─┤ Router ├──►│Gossip├──►│  iroh ├──┤◄──► Other
+              │ Thread ││─►│ (dedup ││  │Swarm │   │  QUIC │  │    Bridges
+              └────────┘│  │  rate  ││  └──┬───┘   └───────┘  │
+                        │  │  limit)│|     │                  │
+                        │  └────────┘│  ┌──┴───┐             │
+                        │     ▲      │  │ DHT  │             │
+                        │     │      │  │(peer │             │
+                        │  ┌──┴──┐   │  │disc.)│             │
+                        │  │ TUI │   │  └──────┘             │
+                        │  └─────┘   │                       │
+                        └─────────────────────────────────────┘
+```
+
+## Testing
+
+```sh
+cargo test                      # unit tests + property tests (proptest)
+cargo clippy --all-targets      # lint check (pedantic + nursery)
+cargo fmt --check               # format check
+cargo mutants                   # mutation testing (install: cargo install cargo-mutants)
+cargo +nightly fuzz run fuzz_gossip_frame_decode   # fuzz testing (requires nightly)
+cargo +nightly fuzz run fuzz_decode_peer_list
+```
+
+## Troubleshooting
+
+| Symptom | Cause | Fix |
+|---------|-------|-----|
+| "passphrase is required" | Empty or placeholder passphrase | Run `donglora-bridge config` |
+| No peers found | Passphrase mismatch or firewall | Check passphrase matches; iroh uses QUIC (UDP), DHT uses UDP |
+| Radio disconnected | USB dongle unplugged or mux crash | Check USB connection; bridge will auto-reconnect |
+| Yellow `!` on radio fields | Mux has different radio config | Another client set different params; bridge adopts mux config |
+| Log file location | Default path | `~/.local/state/donglora-bridge/bridge.log` |
+
+## License
+
+[MIT](LICENSE)

deny.toml

@@ -0,0 +1,39 @@
+# cargo-deny configuration (v0.19+)
+# Run with: cargo deny check
+
+[licenses]
+version = 2
+
+# Permissive licenses only. No copyleft.
+allow = [
+    "MIT",
+    "MIT-0",
+    "Apache-2.0",
+    "BSD-1-Clause",
+    "BSD-2-Clause",
+    "BSD-3-Clause",
+    "BSL-1.0",
+    "ISC",
+    "Zlib",
+    "Unlicense",
+    "CC0-1.0",
+    "CDLA-Permissive-2.0",
+    "Unicode-3.0",
+    "MPL-2.0",
+]
+
+[advisories]
+# Unmaintained transitive deps from upstream (iroh dep tree) — not actionable by us.
+ignore = [
+    "RUSTSEC-2023-0089", # atomic-polyfill: unmaintained (transitive via iroh)
+    "RUSTSEC-2024-0436", # paste: unmaintained (transitive via iroh)
+]
+
+[bans]
+multiple-versions = "warn"
+wildcards = "warn"
+
+[sources]
+unknown-registry = "deny"
+unknown-git = "warn"
+allow-git = []

fuzz/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "donglora-bridge-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2024"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+
+[dependencies.donglora-bridge]
+path = ".."
+
+[[bin]]
+name = "fuzz_gossip_frame_decode"
+path = "fuzz_targets/fuzz_gossip_frame_decode.rs"
+doc = false
+
+[[bin]]
+name = "fuzz_decode_peer_list"
+path = "fuzz_targets/fuzz_decode_peer_list.rs"
+doc = false
+
+[workspace]

fuzz/fuzz_targets/fuzz_decode_peer_list.rs

@@ -0,0 +1,7 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    // decode_peer_list must never panic on arbitrary input.
+    let _ = donglora_bridge::gossip::decode_peer_list(data);
+});

fuzz/fuzz_targets/fuzz_gossip_frame_decode.rs

@@ -0,0 +1,7 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    // GossipFrame::decode must never panic on arbitrary input.
+    let _ = donglora_bridge::packet::GossipFrame::decode(data);
+});

justfile

@@ -0,0 +1,60 @@
+# Default: run all checks
+default: build
+
+# Run all checks (fmt, clippy, test)
+check: fmt-check clippy test audit
+
+# Format code
+fmt:
+    cargo fmt
+
+# Check formatting without changing files
+fmt-check:
+    cargo fmt --check
+
+# Lint with clippy (pedantic + nursery)
+clippy:
+    cargo clippy --all-targets -- -D warnings
+
+# Build release binary
+build:
+    cargo build --release
+
+# Generate docs
+doc:
+    cargo doc --no-deps --open
+
+# Run the bridge (TUI mode)
+run *ARGS:
+    cargo run --release -- {{ARGS}}
+
+# Run in headless mode
+run-headless *ARGS:
+    cargo run --release -- --log-only {{ARGS}}
+
+# Run the config wizard
+config:
+    cargo run --release -- config
+
+# Security + license audit
+audit:
+    cargo deny check
+
+# Run all tests
+test: test-unit test-fuzz test-mutants
+
+# Normal unit tests
+test-unit:
+    cargo nextest run
+
+# Mutation testing
+test-mutants *ARGS:
+    cargo mutants {{ARGS}}
+
+# Fuzz a target (requires nightly)
+test-fuzz TARGET="fuzz_gossip_frame_decode" DURATION="60":
+    cargo +nightly fuzz run {{TARGET}} -- -max_total_time={{DURATION}}
+
+# Clean build artifacts
+clean:
+    cargo clean

rustfmt.toml

@@ -0,0 +1,3 @@
+edition = "2024"
+max_width = 120
+use_small_heuristics = "Max"

src/config.rs

@@ -1,8 +1,12 @@
+//! TOML configuration loading and validation.
+//!
+//! Handles the `[radio]` and `[bridge]` sections with `MeshCore` US/Canada recommended
+//! defaults, and conversion to donglora-client `RadioConfig`.
+
 use std::path::{Path, PathBuf};
 
 use anyhow::{Context, Result, bail};
 use donglora_client::{Bandwidth, RadioConfig, TX_POWER_MAX};
-use iroh::{PublicKey, SecretKey};
 use serde::{Deserialize, Serialize};
 
 /// Top-level bridge configuration.
@@ -12,11 +16,9 @@ pub struct Config {
     pub radio: RadioSection,
     #[serde(default)]
     pub bridge: BridgeSection,
-    #[serde(default)]
-    pub peers: Vec<PeerEntry>,
 }
 
-#[derive(Debug, Deserialize, Serialize)]
+#[derive(Debug, Clone, Deserialize, Serialize)]
 pub struct RadioSection {
     /// Serial port path (auto-detect if omitted).
     pub port: Option<String>,
@@ -32,56 +34,57 @@ pub struct RadioSection {
     pub sync_word: u16,
     #[serde(default = "default_tx_power")]
     pub tx_power: String,
-    #[serde(default)]
+    #[serde(default = "default_preamble")]
     pub preamble: u16,
     #[serde(default = "default_true")]
     pub cad: bool,
 }
 
-#[derive(Debug, Deserialize, Serialize)]
+#[derive(Debug, Clone, Deserialize, Serialize)]
 pub struct BridgeSection {
+    /// Shared passphrase. All bridges with the same passphrase join the same swarm.
+    #[serde(default)]
+    pub passphrase: String,
     #[serde(default = "default_dedup_window")]
     pub dedup_window_secs: u64,
     #[serde(default = "default_tx_queue_size")]
     pub tx_queue_size: usize,
+    /// Optional manual override for the radio TX rate limit (packets per second).
+    /// If omitted, a rate is calculated from the radio config.
+    pub rate_limit_pps: Option<f64>,
     pub log_file: Option<PathBuf>,
 }
 
-#[derive(Debug, Clone, Deserialize, Serialize)]
+// ── Defaults (MeshCore US/Canada Recommended) ────────────────────
-pub struct PeerEntry {
-    pub node_id: String,
-    pub name: Option<String>,
-    #[serde(default)]
-    pub addresses: Vec<String>,
-}
 
-// ── Defaults ──────────────────────────────────────────────────────
+const fn default_frequency() -> u32 {
-
+    910_525_000
-fn default_frequency() -> u32 {
-    915_000_000
 }
 fn default_bandwidth() -> String {
-    "125kHz".into()
+    "62.5kHz".into()
 }
-fn default_sf() -> u8 {
+const fn default_sf() -> u8 {
     7
 }
-fn default_cr() -> u8 {
+const fn default_cr() -> u8 {
     5
 }
-fn default_sync_word() -> u16 {
+const fn default_sync_word() -> u16 {
-    0x1424
+    0x3444
 }
 fn default_tx_power() -> String {
-    "max".into()
+    "22".into()
 }
-fn default_true() -> bool {
+const fn default_preamble() -> u16 {
+    16
+}
+const fn default_true() -> bool {
     true
 }
-fn default_dedup_window() -> u64 {
+const fn default_dedup_window() -> u64 {
-    30
+    300
 }
-fn default_tx_queue_size() -> usize {
+const fn default_tx_queue_size() -> usize {
     32
 }
 
@@ -95,7 +98,7 @@ impl Default for RadioSection {
             coding_rate: default_cr(),
             sync_word: default_sync_word(),
             tx_power: default_tx_power(),
-            preamble: 0,
+            preamble: default_preamble(),
             cad: true,
         }
     }
@@ -104,8 +107,10 @@ impl Default for RadioSection {
 impl Default for BridgeSection {
     fn default() -> Self {
         Self {
+            passphrase: String::new(),
             dedup_window_secs: default_dedup_window(),
             tx_queue_size: default_tx_queue_size(),
+            rate_limit_pps: None,
             log_file: None,
         }
     }
@@ -138,8 +143,20 @@ fn parse_tx_power(s: &str) -> Result<i8> {
 }
 
 impl RadioSection {
-    /// Convert to the donglora-client RadioConfig.
+    /// Convert to the donglora-client `RadioConfig`.
+    ///
+    /// Validates that all radio parameters are within hardware-supported ranges
+    /// before constructing the config.
     pub fn to_radio_config(&self) -> Result<RadioConfig> {
+        if !(7..=12).contains(&self.spreading_factor) {
+            bail!("spreading_factor must be 7-12, got {}", self.spreading_factor);
+        }
+        if !(5..=8).contains(&self.coding_rate) {
+            bail!("coding_rate must be 5-8 (meaning 4/5 to 4/8), got {}", self.coding_rate);
+        }
+        if self.frequency < 150_000_000 || self.frequency > 1_020_000_000 {
+            bail!("frequency {:.3} MHz out of range (150 MHz to 1.02 GHz)", f64::from(self.frequency) / 1_000_000.0);
+        }
         Ok(RadioConfig {
             freq_hz: self.frequency,
             bw: parse_bandwidth(&self.bandwidth)?,
@@ -153,38 +170,11 @@ impl RadioSection {
     }
 }
 
-// ── Peer parsing ──────────────────────────────────────────────────
-
-impl PeerEntry {
-    /// Parse the node_id string into an iroh PublicKey.
-    pub fn public_key(&self) -> Result<PublicKey> {
-        self.node_id
-            .parse::<PublicKey>()
-            .map_err(|e| anyhow::anyhow!("invalid node_id '{}': {e}", self.node_id))
-    }
-
-    /// Display name: the configured name, or a truncated NodeId.
-    pub fn display_name(&self) -> String {
-        if let Some(name) = &self.name {
-            name.clone()
-        } else {
-            let id = &self.node_id;
-            if id.len() > 12 {
-                format!("{}...", &id[..12])
-            } else {
-                id.clone()
-            }
-        }
-    }
-}
-
 // ── File I/O ──────────────────────────────────────────────────────
 
 /// Default config directory: `$XDG_CONFIG_HOME/donglora-bridge/` or `~/.config/donglora-bridge/`.
 pub fn config_dir() -> Result<PathBuf> {
-    let dir = dirs::config_dir()
+    let dir = dirs::config_dir().context("cannot determine config directory")?.join("donglora-bridge");
-        .context("cannot determine config directory")?
-        .join("donglora-bridge");
     Ok(dir)
 }
 
@@ -193,12 +183,6 @@ pub fn config_path() -> Result<PathBuf> {
     Ok(config_dir()?.join("config.toml"))
 }
 
-/// Default secret key file path (alongside default config).
-#[allow(dead_code)]
-pub fn secret_key_path() -> Result<PathBuf> {
-    Ok(config_dir()?.join("config.key"))
-}
-
 /// Default log file path: `$XDG_STATE_HOME/donglora-bridge/bridge.log`.
 pub fn default_log_path() -> Result<PathBuf> {
     let dir = dirs::state_dir()
@@ -208,79 +192,243 @@ pub fn default_log_path() -> Result<PathBuf> {
     Ok(dir.join("bridge.log"))
 }
 
-/// Load config from a TOML file.
+/// Load config from a TOML file. Returns None-passphrase error if not set.
 pub fn load_config(path: &Path) -> Result<Config> {
-    let text = std::fs::read_to_string(path)
+    let text = std::fs::read_to_string(path).with_context(|| format!("reading config: {}", path.display()))?;
-        .with_context(|| format!("reading config: {}", path.display()))?;
+    let cfg: Config = toml::from_str(&text).context("parsing config TOML")?;
-    toml::from_str(&text).context("parsing config TOML")
+    if cfg.bridge.passphrase.is_empty() || cfg.bridge.passphrase == "change-me" {
+        bail!("passphrase is required — run `donglora-bridge config` to set it");
+    }
+    Ok(cfg)
 }
 
-/// Load or generate the persistent secret key.
+#[cfg(test)]
-pub fn load_or_create_secret_key(path: &Path) -> Result<SecretKey> {
+#[allow(clippy::unwrap_used, clippy::expect_used)]
-    if path.exists() {
+mod tests {
-        let hex = std::fs::read_to_string(path)
+    use super::*;
-            .with_context(|| format!("reading secret key: {}", path.display()))?;
+
-        let hex = hex.trim();
+    #[test]
-        let bytes = hex::decode(hex).context("decoding secret key hex")?;
+    fn parse_bandwidth_canonical() {
-        let arr: [u8; 32] = bytes
+        assert!(matches!(parse_bandwidth("7.8kHz"), Ok(Bandwidth::Khz7)));
-            .try_into()
+        assert!(matches!(parse_bandwidth("62.5kHz"), Ok(Bandwidth::Khz62)));
-            .map_err(|_| anyhow::anyhow!("secret key must be 32 bytes"))?;
+        assert!(matches!(parse_bandwidth("125kHz"), Ok(Bandwidth::Khz125)));
-        Ok(SecretKey::from_bytes(&arr))
+        assert!(matches!(parse_bandwidth("500kHz"), Ok(Bandwidth::Khz500)));
-    } else {
-        let key = SecretKey::generate(&mut rand::rng());
-        if let Some(parent) = path.parent() {
-            std::fs::create_dir_all(parent)
-                .with_context(|| format!("creating directory: {}", parent.display()))?;
-        }
-        let hex = hex::encode(key.to_bytes());
-        std::fs::write(path, &hex)
-            .with_context(|| format!("writing secret key: {}", path.display()))?;
-        Ok(key)
-    }
     }
 
-/// Generate a default config file with the given NodeId embedded as a comment.
+    #[test]
-pub fn generate_default_config(node_id: &str) -> String {
+    fn parse_bandwidth_aliases() {
-    format!(
+        assert!(matches!(parse_bandwidth("7khz"), Ok(Bandwidth::Khz7)));
-        r#"# donglora-bridge configuration
+        assert!(matches!(parse_bandwidth("khz125"), Ok(Bandwidth::Khz125)));
-# Auto-generated — add peers to get started!
+        assert!(matches!(parse_bandwidth("10khz"), Ok(Bandwidth::Khz10)));
-# Your NodeId: {node_id}
+    }
 
+    #[test]
+    fn parse_bandwidth_case_insensitive() {
+        assert!(matches!(parse_bandwidth("125KHZ"), Ok(Bandwidth::Khz125)));
+        assert!(matches!(parse_bandwidth("62.5KHZ"), Ok(Bandwidth::Khz62)));
+    }
+
+    #[test]
+    fn parse_bandwidth_rejects_unknown() {
+        assert!(parse_bandwidth("999kHz").is_err());
+        assert!(parse_bandwidth("").is_err());
+        assert!(parse_bandwidth("not_a_bandwidth").is_err());
+    }
+
+    #[test]
+    fn parse_tx_power_numeric() {
+        assert_eq!(parse_tx_power("22").unwrap(), 22);
+        assert_eq!(parse_tx_power("-4").unwrap(), -4);
+        assert_eq!(parse_tx_power("0").unwrap(), 0);
+    }
+
+    #[test]
+    fn parse_tx_power_max_keyword() {
+        assert_eq!(parse_tx_power("max").unwrap(), TX_POWER_MAX);
+        assert_eq!(parse_tx_power("MAX").unwrap(), TX_POWER_MAX);
+        assert_eq!(parse_tx_power("Max").unwrap(), TX_POWER_MAX);
+    }
+
+    #[test]
+    fn parse_tx_power_rejects_garbage() {
+        assert!(parse_tx_power("abc").is_err());
+        assert!(parse_tx_power("").is_err());
+    }
+
+    #[test]
+    fn radio_section_defaults_to_radio_config() {
+        let section = RadioSection::default();
+        let config = section.to_radio_config().unwrap();
+        assert_eq!(config.freq_hz, 910_525_000);
+        assert_eq!(config.sf, 7);
+        assert_eq!(config.cr, 5);
+        assert_eq!(config.sync_word, 0x3444);
+        assert_eq!(config.preamble_len, 16);
+    }
+
+    #[test]
+    fn radio_section_max_power() {
+        let section = RadioSection { tx_power: "max".into(), ..RadioSection::default() };
+        let config = section.to_radio_config().unwrap();
+        assert_eq!(config.tx_power_dbm, TX_POWER_MAX);
+    }
+
+    #[test]
+    fn to_radio_config_rejects_invalid_sf() {
+        let section = RadioSection { spreading_factor: 6, ..RadioSection::default() };
+        assert!(section.to_radio_config().is_err());
+        let section = RadioSection { spreading_factor: 13, ..RadioSection::default() };
+        assert!(section.to_radio_config().is_err());
+    }
+
+    #[test]
+    fn to_radio_config_rejects_invalid_cr() {
+        let section = RadioSection { coding_rate: 4, ..RadioSection::default() };
+        assert!(section.to_radio_config().is_err());
+        let section = RadioSection { coding_rate: 9, ..RadioSection::default() };
+        assert!(section.to_radio_config().is_err());
+    }
+
+    #[test]
+    fn to_radio_config_rejects_invalid_frequency() {
+        let section = RadioSection { frequency: 0, ..RadioSection::default() };
+        assert!(section.to_radio_config().is_err());
+        let section = RadioSection { frequency: 2_000_000_000, ..RadioSection::default() };
+        assert!(section.to_radio_config().is_err());
+    }
+
+    #[test]
+    fn load_config_valid_minimal() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.toml");
+        std::fs::write(&path, "[bridge]\npassphrase = \"my-secret\"\n").unwrap();
+        let cfg = load_config(&path).unwrap();
+        assert_eq!(cfg.bridge.passphrase, "my-secret");
+        assert_eq!(cfg.radio.frequency, 910_525_000);
+    }
+
+    #[test]
+    fn load_config_empty_passphrase_rejected() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.toml");
+        std::fs::write(&path, "[bridge]\npassphrase = \"\"\n").unwrap();
+        assert!(load_config(&path).is_err());
+    }
+
+    #[test]
+    fn load_config_change_me_rejected() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.toml");
+        std::fs::write(&path, "[bridge]\npassphrase = \"change-me\"\n").unwrap();
+        assert!(load_config(&path).is_err());
+    }
+
+    #[test]
+    fn load_config_missing_file() {
+        assert!(load_config(std::path::Path::new("/nonexistent/config.toml")).is_err());
+    }
+
+    #[test]
+    fn load_config_invalid_toml() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.toml");
+        std::fs::write(&path, "not valid toml {{{{").unwrap();
+        assert!(load_config(&path).is_err());
+    }
+
+    // ── Mutant killers: default values (items 1-5) ─────────────────
+
+    #[test]
+    fn default_radio_cad_is_true() {
+        let radio = RadioSection::default();
+        assert!(radio.cad);
+        // Also test via serde (exercises the default_true function used by #[serde(default)])
+        let radio: RadioSection = toml::from_str("").unwrap();
+        assert!(radio.cad);
+    }
+
+    #[test]
+    fn default_dedup_window_is_300() {
+        let bridge = BridgeSection::default();
+        assert_eq!(bridge.dedup_window_secs, 300);
+    }
+
+    #[test]
+    fn default_tx_queue_size_is_32() {
+        let bridge = BridgeSection::default();
+        assert_eq!(bridge.tx_queue_size, 32);
+    }
+
+    // ── Mutant killers: missing bandwidth variants (items 6-10) ──
+
+    #[test]
+    fn parse_bandwidth_all_canonical_variants() {
+        assert!(matches!(parse_bandwidth("15.6kHz"), Ok(Bandwidth::Khz15)));
+        assert!(matches!(parse_bandwidth("20.8kHz"), Ok(Bandwidth::Khz20)));
+        assert!(matches!(parse_bandwidth("31.25kHz"), Ok(Bandwidth::Khz31)));
+        assert!(matches!(parse_bandwidth("41.7kHz"), Ok(Bandwidth::Khz41)));
+        assert!(matches!(parse_bandwidth("250kHz"), Ok(Bandwidth::Khz250)));
+    }
+
+    // ── Mutant killers: frequency boundary (items 11-12) ─────────
+
+    #[test]
+    fn to_radio_config_accepts_boundary_frequencies() {
+        let low = RadioSection { frequency: 150_000_000, ..RadioSection::default() };
+        assert!(low.to_radio_config().is_ok());
+
+        let high = RadioSection { frequency: 1_020_000_000, ..RadioSection::default() };
+        assert!(high.to_radio_config().is_ok());
+    }
+
+    // ── Mutant killers: path helpers (items 13-15) ───────────────
+
+    #[test]
+    fn config_dir_is_non_empty() {
+        let dir = config_dir().unwrap();
+        assert!(dir.components().count() > 0);
+    }
+
+    #[test]
+    fn config_path_ends_with_config_toml() {
+        let path = config_path().unwrap();
+        assert_eq!(path.file_name().unwrap(), "config.toml");
+    }
+
+    #[test]
+    fn default_log_path_ends_with_bridge_log() {
+        let path = default_log_path().unwrap();
+        assert_eq!(path.file_name().unwrap(), "bridge.log");
+    }
+
+    #[test]
+    fn load_config_full_round_trip() {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("config.toml");
+        std::fs::write(
+            &path,
+            r#"
 [radio]
-# port = "/dev/ttyACM0"        # auto-detect if omitted
+frequency = 915000000
-frequency = 915_000_000
 bandwidth = "125kHz"
-spreading_factor = 7
+spreading_factor = 12
-coding_rate = 5
+coding_rate = 8
-sync_word = 0x1424
+sync_word = 0x1234
 tx_power = "max"
-preamble = 0                    # 0 = firmware default (16 symbols)
+preamble = 8
-cad = true
+cad = false
 
 [bridge]
-dedup_window_secs = 30
+passphrase = "test-phrase"
-tx_queue_size = 32
+dedup_window_secs = 600
-# log_file = "/tmp/donglora-bridge.log"
+tx_queue_size = 64
-
+"#,
-# Add peers below. Each peer needs the remote bridge's NodeId.
-# Share your NodeId (above) with peers so they can add you too.
-#
-# [[peers]]
-# node_id = "paste-node-id-here"
-# name = "My Friend's Bridge"
-# addresses = ["1.2.3.4:1234"]  # optional direct address hints
-"#
         )
+        .unwrap();
+        let cfg = load_config(&path).unwrap();
+        assert_eq!(cfg.radio.frequency, 915_000_000);
+        assert_eq!(cfg.radio.spreading_factor, 12);
+        assert_eq!(cfg.bridge.dedup_window_secs, 600);
+        assert_eq!(cfg.bridge.tx_queue_size, 64);
     }
-
-/// Write the default config to disk (first-run flow).
-pub fn write_default_config(path: &Path, node_id: &str) -> Result<()> {
-    if let Some(parent) = path.parent() {
-        std::fs::create_dir_all(parent)
-            .with_context(|| format!("creating directory: {}", parent.display()))?;
-    }
-    let content = generate_default_config(node_id);
-    std::fs::write(path, content)
-        .with_context(|| format!("writing config: {}", path.display()))?;
-    Ok(())
 }

src/gossip.rs

@@ -0,0 +1,769 @@
+//! iroh-gossip swarm management and mainline DHT peer discovery.
+//!
+//! Derives cryptographic keys from a shared passphrase, manages the gossip
+//! subscription, and maintains a DHT heartbeat for zero-configuration peer
+//! bootstrapping.
+
+use std::collections::HashSet;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::{Arc, Mutex};
+use std::time::{Duration, Instant};
+
+use anyhow::{Context, Result};
+use bytes::Bytes;
+use futures_lite::StreamExt;
+use iroh::endpoint::Incoming;
+use iroh::{Endpoint, PublicKey, SecretKey};
+use iroh_gossip::TopicId;
+use iroh_gossip::api::Event;
+use iroh_gossip::net::{GOSSIP_ALPN, Gossip as GossipActor};
+use mainline::async_dht::AsyncDht;
+use mainline::{Dht, MutableItem, SigningKey};
+use sha2::{Digest, Sha256};
+use tokio::sync::mpsc;
+use tokio_util::sync::CancellationToken;
+use tracing::{debug, info, warn};
+
+use crate::packet::GossipFrame;
+
+/// Maximum number of peers to store in a DHT record.
+/// 28 × 32 bytes = 896 bytes raw. Bencoded: 28 × ~36 = ~1008.
+/// Conservative cap to stay under BEP44's 1000-byte value limit.
+const MAX_DHT_PEERS: usize = 27;
+
+/// DHT heartbeat interval when connected (base, before jitter). 5 minutes
+/// balances freshness against DHT write amplification — connected nodes already
+/// have live gossip links and only need DHT for newcomer discovery.
+const DHT_HEARTBEAT_SECS: u64 = 300;
+
+/// Maximum random jitter added to heartbeat interval. Prevents synchronized
+/// publish storms when multiple bridges start simultaneously.
+const DHT_HEARTBEAT_JITTER_SECS: u64 = 60;
+
+// ── Key derivation ───────────────────────────────────────────────
+
+/// Cryptographic keys derived from a shared passphrase.
+pub struct PassphraseKeys {
+    pub topic_id: TopicId,
+    pub dht_signing_key: SigningKey,
+    pub dht_salt: [u8; 20],
+}
+
+impl PassphraseKeys {
+    /// Derive all keys from a passphrase.
+    ///
+    /// Intermediate buffers containing the passphrase are zeroized after use to
+    /// minimize time sensitive material spends in memory.
+    #[must_use]
+    pub fn derive(passphrase: &str) -> Self {
+        // Application-specific prefix to avoid DHT collisions with other apps.
+        const APP_PREFIX: &[u8] = b"donglora-bridge:";
+
+        // Helper: build a zeroized buffer of [prefix | suffix | passphrase].
+        let keyed_buf = |suffix: &[u8]| -> Vec<u8> {
+            let mut buf = Vec::with_capacity(APP_PREFIX.len() + suffix.len() + passphrase.len());
+            buf.extend_from_slice(APP_PREFIX);
+            buf.extend_from_slice(suffix);
+            buf.extend_from_slice(passphrase.as_bytes());
+            buf
+        };
+
+        // Topic ID: blake3 hash of prefixed passphrase.
+        let mut buf = keyed_buf(b"");
+        let topic_bytes = *blake3::hash(&buf).as_bytes();
+        let topic_id = TopicId::from_bytes(topic_bytes);
+        zeroize::Zeroize::zeroize(&mut buf);
+
+        // DHT signing key: ed25519 from SHA-256 of prefixed passphrase + "sign:".
+        let mut buf = keyed_buf(b"sign:");
+        let sign_seed = Sha256::digest(&buf);
+        let seed_bytes: [u8; 32] = sign_seed.into();
+        let dht_signing_key = SigningKey::from_bytes(&seed_bytes);
+        zeroize::Zeroize::zeroize(&mut buf);
+
+        // DHT salt: first 20 bytes of SHA-256 of prefixed passphrase + "salt:".
+        let mut buf = keyed_buf(b"salt:");
+        let salt_hash = Sha256::digest(&buf);
+        let mut dht_salt = [0u8; 20];
+        dht_salt.copy_from_slice(&salt_hash[..20]);
+        zeroize::Zeroize::zeroize(&mut buf);
+
+        Self { topic_id, dht_signing_key, dht_salt }
+    }
+}
+
+// ── Swarm state (for TUI) ───────────────────────────────────────
+
+/// Observable state of the gossip swarm.
+#[derive(Debug, Clone)]
+pub struct SwarmState {
+    pub topic_hash: String,
+    pub neighbor_count: usize,
+    pub dht_status: DhtStatus,
+    pub last_dht_publish: Option<Instant>,
+}
+
+/// Status of the mainline DHT connection.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum DhtStatus {
+    Bootstrapping,
+    Ready,
+    PublishFailed,
+}
+
+impl std::fmt::Display for DhtStatus {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Bootstrapping => write!(f, "Bootstrapping"),
+            Self::Ready => write!(f, "Ready"),
+            Self::PublishFailed => write!(f, "Failed"),
+        }
+    }
+}
+
+// ── Events to router ────────────────────────────────────────────
+
+/// Events from the gossip swarm to the router.
+pub enum GossipEvent {
+    /// A gossip frame received from the swarm.
+    Frame(GossipFrame),
+    /// Neighbor count changed.
+    NeighborChanged(usize),
+}
+
+// ── Gossip handle ───────────────────────────────────────────────
+
+/// Handle to the gossip swarm. Manages iroh endpoint, gossip subscription, and DHT.
+pub struct Gossip {
+    endpoint: Endpoint,
+    actor: GossipActor,
+    // std::sync::Mutex (not tokio::sync::Mutex) because locks are never held across
+    // .await points. This avoids async-aware mutex overhead for brief critical sections.
+    state: Arc<Mutex<SwarmState>>,
+    neighbors: Arc<Mutex<HashSet<PublicKey>>>,
+    dht_signing_key: SigningKey,
+    dht_salt: [u8; 20],
+    cancel: CancellationToken,
+}
+
+impl Gossip {
+    /// Create and start the gossip network.
+    ///
+    /// Spawns background tasks for connection acceptance, gossip event forwarding,
+    /// gossip broadcasting, and DHT heartbeat.
+    ///
+    /// Returns `(handle, event_rx, frame_tx)`:
+    /// - `event_rx`: channel of events from the swarm to the router
+    /// - `frame_tx`: channel for the router to send frames to broadcast
+    pub async fn new(
+        secret_key: SecretKey,
+        keys: &PassphraseKeys,
+    ) -> Result<(Self, mpsc::Receiver<GossipEvent>, mpsc::Sender<GossipFrame>)> {
+        let cancel = CancellationToken::new();
+
+        // Build iroh endpoint with n0 discovery.
+        let endpoint = Endpoint::builder(iroh::endpoint::presets::N0)
+            .secret_key(secret_key)
+            .alpns(vec![GOSSIP_ALPN.to_vec()])
+            .bind()
+            .await
+            .context("binding iroh endpoint")?;
+
+        let my_id = endpoint.id();
+        info!("iroh endpoint bound, id: {}", my_id.fmt_short());
+
+        // Build gossip actor.
+        let actor = GossipActor::builder().spawn(endpoint.clone());
+
+        // Bootstrap from DHT.
+        let bootstrap_peers = dht_get_peers(keys).await;
+        if bootstrap_peers.is_empty() {
+            info!("no peers found in DHT — we are the first node");
+        } else {
+            info!("found {} peer(s) in DHT", bootstrap_peers.len());
+        }
+
+        // Subscribe to gossip topic.
+        let topic = actor.subscribe(keys.topic_id, bootstrap_peers).await.context("subscribing to gossip topic")?;
+
+        let (sender, receiver) = topic.split();
+
+        // Initial swarm state.
+        let topic_hash = hex::encode(&keys.topic_id.as_bytes()[..8]);
+        let state = Arc::new(Mutex::new(SwarmState {
+            topic_hash,
+            neighbor_count: 0,
+            dht_status: DhtStatus::Bootstrapping,
+            last_dht_publish: None,
+        }));
+        let neighbor_count = Arc::new(AtomicUsize::new(0));
+        let neighbors: Arc<Mutex<HashSet<PublicKey>>> = Arc::new(Mutex::new(HashSet::new()));
+
+        // Channels.
+        let (event_tx, event_rx) = mpsc::channel::<GossipEvent>(256);
+        let (frame_tx, frame_rx) = mpsc::channel::<GossipFrame>(256);
+
+        let handle = Self {
+            endpoint: endpoint.clone(),
+            actor: actor.clone(),
+            state: state.clone(),
+            neighbors: neighbors.clone(),
+            dht_signing_key: keys.dht_signing_key.clone(),
+            dht_salt: keys.dht_salt,
+            cancel: cancel.clone(),
+        };
+
+        // Spawn accept loop.
+        spawn_accept_loop(endpoint.clone(), actor.clone(), cancel.clone());
+
+        // Spawn gossip receiver task.
+        spawn_receiver(receiver, event_tx, state.clone(), neighbor_count.clone(), neighbors.clone(), cancel.clone());
+
+        // Clone sender for DHT heartbeat to feed discovered peers via join_peers.
+        let dht_sender = sender.clone();
+
+        // Spawn gossip broadcaster task.
+        spawn_broadcaster(sender, frame_rx, cancel.clone());
+
+        // Spawn DHT heartbeat.
+        spawn_dht_heartbeat(
+            my_id,
+            keys.dht_signing_key.clone(),
+            keys.dht_salt,
+            dht_sender,
+            neighbors,
+            state,
+            neighbor_count,
+            cancel,
+        );
+
+        // Try to join (non-blocking — fire and forget with timeout).
+        // The receiver task handles events regardless.
+
+        Ok((handle, event_rx, frame_tx))
+    }
+
+    /// Snapshot of swarm state for TUI.
+    #[must_use]
+    pub fn swarm_state(&self) -> SwarmState {
+        self.state.lock().unwrap_or_else(std::sync::PoisonError::into_inner).clone()
+    }
+
+    /// Graceful shutdown. Publishes neighbors (without ourselves) to DHT
+    /// so other nodes can still bootstrap from live peers.
+    pub async fn shutdown(&self) {
+        // Publish neighbors-only to DHT before shutting down.
+        let neighbor_ids: Vec<[u8; 32]> = self
+            .neighbors
+            .lock()
+            .unwrap_or_else(std::sync::PoisonError::into_inner)
+            .iter()
+            .map(|id| *id.as_bytes())
+            .collect();
+
+        if let Ok(dht) = Dht::client() {
+            let dht = dht.as_async();
+            let value = encode_peer_list(&neighbor_ids);
+            let seq = std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .map(|d| d.as_secs().cast_signed())
+                .unwrap_or(0);
+            let item = MutableItem::new(self.dht_signing_key.clone(), &value, seq, Some(self.dht_salt.as_ref()));
+            match dht.put_mutable(item, None).await {
+                Ok(_) => info!("shutdown: published {} neighbor(s) to DHT (removed self)", neighbor_ids.len()),
+                Err(e) => debug!("shutdown: DHT publish failed: {e:#}"),
+            }
+        }
+
+        self.cancel.cancel();
+        let _ = self.actor.shutdown().await;
+        self.endpoint.close().await;
+    }
+}
+
+// ── Background tasks ────────────────────────────────────────────
+
+/// Accept incoming iroh connections and forward gossip ALPN to the gossip actor.
+fn spawn_accept_loop(endpoint: Endpoint, gossip: GossipActor, cancel: CancellationToken) {
+    tokio::spawn(async move {
+        loop {
+            let incoming = tokio::select! {
+                incoming = endpoint.accept() => incoming,
+                () = cancel.cancelled() => break,
+            };
+            let Some(incoming) = incoming else { break };
+            let gossip = gossip.clone();
+            tokio::spawn(handle_incoming(incoming, gossip));
+        }
+        debug!("accept loop stopped");
+    });
+}
+
+async fn handle_incoming(incoming: Incoming, gossip: GossipActor) {
+    let Ok(conn) = incoming.await else { return };
+    let alpn = conn.alpn();
+    if *alpn == *GOSSIP_ALPN {
+        if let Err(e) = gossip.handle_connection(conn).await {
+            debug!("gossip handle_connection error: {e:#}");
+        }
+    } else {
+        debug!("unexpected ALPN: {:?}", String::from_utf8_lossy(alpn));
+    }
+}
+
+/// Forward gossip events to the router via channel.
+fn spawn_receiver(
+    mut receiver: iroh_gossip::api::GossipReceiver,
+    event_tx: mpsc::Sender<GossipEvent>,
+    state: Arc<Mutex<SwarmState>>,
+    neighbor_count: Arc<AtomicUsize>,
+    neighbors: Arc<Mutex<HashSet<PublicKey>>>,
+    cancel: CancellationToken,
+) {
+    tokio::spawn(async move {
+        loop {
+            let event = tokio::select! {
+                event = receiver.next() => event,
+                () = cancel.cancelled() => break,
+            };
+            let Some(Ok(event)) = event else { break };
+            match event {
+                Event::Received(msg) => {
+                    if let Some(frame) = GossipFrame::decode(&msg.content) {
+                        let _ = event_tx.send(GossipEvent::Frame(frame)).await;
+                    } else {
+                        debug!("received malformed gossip frame ({} bytes)", msg.content.len());
+                    }
+                }
+                // Neighbor count is tracked in both AtomicUsize (for lock-free reads in DHT
+                // heartbeat) and SwarmState (for TUI snapshots). Brief inconsistency between
+                // the two is acceptable — the TUI polls at 250ms intervals.
+                Event::NeighborUp(id) => {
+                    let count = neighbor_count.fetch_add(1, Ordering::Relaxed) + 1;
+                    info!("neighbor up: {} (total: {count})", id.fmt_short());
+                    if let Ok(mut n) = neighbors.lock() {
+                        n.insert(id);
+                    }
+                    if let Ok(mut s) = state.lock() {
+                        s.neighbor_count = count;
+                    }
+                    let _ = event_tx.send(GossipEvent::NeighborChanged(count)).await;
+                }
+                Event::NeighborDown(id) => {
+                    let count = neighbor_count.fetch_sub(1, Ordering::Relaxed).saturating_sub(1);
+                    info!("neighbor down: {} (total: {count})", id.fmt_short());
+                    if let Ok(mut n) = neighbors.lock() {
+                        n.remove(&id);
+                    }
+                    if let Ok(mut s) = state.lock() {
+                        s.neighbor_count = count;
+                    }
+                    let _ = event_tx.send(GossipEvent::NeighborChanged(count)).await;
+                }
+                Event::Lagged => {
+                    warn!("gossip receiver lagged — some messages were dropped");
+                }
+            }
+        }
+        debug!("gossip receiver stopped");
+    });
+}
+
+/// Read frames from the router and broadcast them to the swarm.
+fn spawn_broadcaster(
+    sender: iroh_gossip::api::GossipSender,
+    mut frame_rx: mpsc::Receiver<GossipFrame>,
+    cancel: CancellationToken,
+) {
+    tokio::spawn(async move {
+        loop {
+            let frame = tokio::select! {
+                frame = frame_rx.recv() => frame,
+                () = cancel.cancelled() => break,
+            };
+            let Some(frame) = frame else { break };
+            let encoded = Bytes::from(frame.encode());
+            if let Err(e) = sender.broadcast(encoded).await {
+                debug!("gossip broadcast error: {e:#}");
+            }
+        }
+        debug!("gossip broadcaster stopped");
+    });
+}
+
+/// DHT poll interval while alone. 3 seconds is aggressive but reads are cheap
+/// (single DHT GET) and fast discovery matters when two nodes start together.
+const DHT_ALONE_READ_SECS: u64 = 3;
+
+/// How often a lonely node publishes (merge-only, never destructive). 30 seconds
+/// is much slower than reads because DHT PUT is heavier and a lonely node only
+/// adds itself to the peer list.
+const DHT_ALONE_PUBLISH_SECS: u64 = 30;
+
+/// Periodically interact with the DHT to discover and share peers.
+///
+/// Strategy:
+/// - **Alone:** Read every 3s (cheap). Publish every 30s via merge — reads
+///   existing data first, appends ourselves, writes back. Two fresh nodes
+///   both doing this will eventually see each other. Never blindly overwrites.
+/// - **Connected:** Read + publish on relaxed 5-min schedule. We have
+///   valuable neighbor info to share.
+/// - **Transition to connected:** Publish immediately.
+#[allow(clippy::too_many_arguments)]
+fn spawn_dht_heartbeat(
+    my_id: PublicKey,
+    signing_key: SigningKey,
+    salt: [u8; 20],
+    gossip_sender: iroh_gossip::api::GossipSender,
+    neighbors: Arc<Mutex<HashSet<PublicKey>>>,
+    state: Arc<Mutex<SwarmState>>,
+    neighbor_count: Arc<AtomicUsize>,
+    cancel: CancellationToken,
+) {
+    tokio::spawn(async move {
+        let dht = match Dht::client() {
+            Ok(d) => d.as_async(),
+            Err(e) => {
+                warn!("failed to create DHT client: {e:#}");
+                return;
+            }
+        };
+
+        let pub_key_bytes = signing_key.verifying_key().to_bytes();
+        let mut was_alone = true;
+        let mut last_publish = Instant::now();
+
+        // Initial: read to discover existing peers, then merge-publish ourselves.
+        dht_read_and_join(&dht, &my_id, &pub_key_bytes, &salt, &gossip_sender, &state).await;
+        dht_publish(&dht, &my_id, &signing_key, &salt, &pub_key_bytes, &neighbors, &state).await;
+
+        loop {
+            let alone = neighbor_count.load(Ordering::Relaxed) == 0;
+
+            // Transition: alone → connected. Publish immediately.
+            if was_alone && !alone {
+                info!("first neighbor joined — publishing to DHT");
+                dht_publish(&dht, &my_id, &signing_key, &salt, &pub_key_bytes, &neighbors, &state).await;
+                last_publish = Instant::now();
+            }
+            was_alone = alone;
+
+            // Sleep: fast reads while alone, relaxed when connected.
+            let sleep_dur = if alone {
+                Duration::from_secs(DHT_ALONE_READ_SECS)
+            } else {
+                let jitter = rand::random::<u64>() % DHT_HEARTBEAT_JITTER_SECS.max(1);
+                Duration::from_secs(DHT_HEARTBEAT_SECS + jitter)
+            };
+
+            tokio::select! {
+                () = tokio::time::sleep(sleep_dur) => {}
+                () = cancel.cancelled() => break,
+            }
+
+            // Always read — cheap, discovers peers to join.
+            dht_read_and_join(&dht, &my_id, &pub_key_bytes, &salt, &gossip_sender, &state).await;
+
+            // Publish cadence depends on state.
+            let publish_interval = if alone {
+                Duration::from_secs(DHT_ALONE_PUBLISH_SECS)
+            } else {
+                Duration::from_secs(DHT_HEARTBEAT_SECS)
+            };
+            if last_publish.elapsed() >= publish_interval {
+                dht_publish(&dht, &my_id, &signing_key, &salt, &pub_key_bytes, &neighbors, &state).await;
+                last_publish = Instant::now();
+            }
+        }
+        debug!("DHT heartbeat stopped");
+    });
+}
+
+/// Read the DHT and feed any discovered peers into the gossip swarm.
+async fn dht_read_and_join(
+    dht: &AsyncDht,
+    my_id: &PublicKey,
+    pub_key_bytes: &[u8; 32],
+    salt: &[u8; 20],
+    gossip_sender: &iroh_gossip::api::GossipSender,
+    state: &Arc<Mutex<SwarmState>>,
+) {
+    if let Some(record) = dht.get_mutable_most_recent(pub_key_bytes, Some(salt)).await {
+        let peers = decode_peer_list(record.value());
+        let new_peers: Vec<_> = peers.into_iter().filter(|id| *id != *my_id).collect();
+        if !new_peers.is_empty() {
+            info!("DHT discovered {} peer(s), feeding to gossip", new_peers.len());
+            if let Err(e) = gossip_sender.join_peers(new_peers).await {
+                debug!("join_peers error: {e:#}");
+            }
+        }
+        if let Ok(mut s) = state.lock() {
+            s.dht_status = DhtStatus::Ready;
+        }
+    }
+}
+
+async fn dht_publish(
+    dht: &AsyncDht,
+    my_id: &PublicKey,
+    signing_key: &SigningKey,
+    salt: &[u8; 20],
+    pub_key_bytes: &[u8; 32],
+    neighbors: &Arc<Mutex<HashSet<PublicKey>>>,
+    state: &Arc<Mutex<SwarmState>>,
+) {
+    let has_neighbors = neighbors.lock().is_ok_and(|n| !n.is_empty());
+
+    let mut seen = HashSet::new();
+    let mut peer_list: Vec<[u8; 32]> = Vec::with_capacity(MAX_DHT_PEERS);
+
+    // Always include ourselves.
+    peer_list.push(*my_id.as_bytes());
+    seen.insert(*my_id.as_bytes());
+
+    if has_neighbors {
+        // Connected: publish authoritative data — self + live neighbors only.
+        // This purges dead/stale peers from the DHT. We know who's alive
+        // because they're our active gossip neighbors.
+        if let Ok(n) = neighbors.lock() {
+            for id in n.iter() {
+                if seen.insert(*id.as_bytes()) && peer_list.len() < MAX_DHT_PEERS {
+                    peer_list.push(*id.as_bytes());
+                }
+            }
+        }
+    } else {
+        // Alone: merge-publish — read existing DHT data first, add ourselves,
+        // preserve other peers. We don't know who's alive so we can't purge.
+        if let Some(record) = dht.get_mutable_most_recent(pub_key_bytes, Some(salt)).await {
+            for existing in decode_peer_list(record.value()) {
+                if seen.insert(*existing.as_bytes()) && peer_list.len() < MAX_DHT_PEERS {
+                    peer_list.push(*existing.as_bytes());
+                }
+            }
+        }
+    }
+
+    let value = encode_peer_list(&peer_list);
+    let seq = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|d| d.as_secs().cast_signed())
+        .unwrap_or(0);
+
+    let item = MutableItem::new(signing_key.clone(), &value, seq, Some(salt.as_ref()));
+    match dht.put_mutable(item, None).await {
+        Ok(_) => {
+            debug!("published to DHT (seq={seq}, peers={})", peer_list.len());
+            if let Ok(mut s) = state.lock() {
+                s.dht_status = DhtStatus::Ready;
+                s.last_dht_publish = Some(Instant::now());
+            }
+        }
+        Err(e) => {
+            warn!("DHT publish failed: {e:#}");
+            if let Ok(mut s) = state.lock() {
+                s.dht_status = DhtStatus::PublishFailed;
+            }
+        }
+    }
+}
+
+// ── DHT helpers ─────────────────────────────────────────────────
+
+/// Query the DHT for existing peers (blocking bootstrap, called once on startup).
+async fn dht_get_peers(keys: &PassphraseKeys) -> Vec<PublicKey> {
+    let dht = match Dht::client() {
+        Ok(d) => d.as_async(),
+        Err(e) => {
+            warn!("failed to create DHT client for bootstrap: {e:#}");
+            return vec![];
+        }
+    };
+
+    let pub_key_bytes = keys.dht_signing_key.verifying_key().to_bytes();
+    dht.get_mutable_most_recent(&pub_key_bytes, Some(&keys.dht_salt)).await.map_or_else(
+        || {
+            debug!("DHT bootstrap: no existing record");
+            vec![]
+        },
+        |record| {
+            let peers = decode_peer_list(record.value());
+            debug!("DHT bootstrap: found {} peer(s)", peers.len());
+            peers
+        },
+    )
+}
+
+/// Encode a list of 32-byte peer IDs into bytes for DHT storage.
+/// Format: `[count: u16 LE] [id_0: 32B] [id_1: 32B] ...`
+#[must_use]
+pub fn encode_peer_list(peers: &[[u8; 32]]) -> Vec<u8> {
+    #[allow(clippy::cast_possible_truncation)] // MAX_DHT_PEERS (27) fits in u16
+    let count = peers.len().min(MAX_DHT_PEERS) as u16;
+    let mut buf = Vec::with_capacity(2 + (count as usize) * 32);
+    buf.extend_from_slice(&count.to_le_bytes());
+    for id in peers.iter().take(MAX_DHT_PEERS) {
+        buf.extend_from_slice(id);
+    }
+    buf
+}
+
+/// Decode a peer list from DHT record value.
+#[must_use]
+pub fn decode_peer_list(data: &[u8]) -> Vec<PublicKey> {
+    if data.len() < 2 {
+        return vec![];
+    }
+    let count = u16::from_le_bytes([data[0], data[1]]) as usize;
+    let mut peers = Vec::with_capacity(count);
+    let mut offset = 2;
+    for _ in 0..count {
+        if offset + 32 > data.len() {
+            break;
+        }
+        let bytes: [u8; 32] = match data[offset..offset + 32].try_into() {
+            Ok(b) => b,
+            Err(_) => break,
+        };
+        if let Ok(pk) = PublicKey::from_bytes(&bytes) {
+            peers.push(pk);
+        }
+        offset += 32;
+    }
+    peers
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn passphrase_keys_deterministic() {
+        let k1 = PassphraseKeys::derive("test-passphrase");
+        let k2 = PassphraseKeys::derive("test-passphrase");
+        assert_eq!(k1.topic_id, k2.topic_id);
+        assert_eq!(k1.dht_signing_key.to_bytes(), k2.dht_signing_key.to_bytes());
+        assert_eq!(k1.dht_salt, k2.dht_salt);
+    }
+
+    #[test]
+    fn passphrase_keys_different() {
+        let k1 = PassphraseKeys::derive("alpha");
+        let k2 = PassphraseKeys::derive("beta");
+        assert_ne!(k1.topic_id, k2.topic_id);
+        assert_ne!(k1.dht_signing_key.to_bytes(), k2.dht_signing_key.to_bytes());
+    }
+
+    #[test]
+    fn peer_list_roundtrip() {
+        // Generate valid ed25519 public keys.
+        let keys: Vec<_> = (0..3)
+            .map(|_| {
+                let sk = iroh::SecretKey::generate(&mut rand::rng());
+                *sk.public().as_bytes()
+            })
+            .collect();
+        let encoded = encode_peer_list(&keys);
+        let decoded = decode_peer_list(&encoded);
+        assert_eq!(decoded.len(), 3);
+        for (i, key) in keys.iter().enumerate() {
+            assert_eq!(*decoded[i].as_bytes(), *key);
+        }
+    }
+
+    #[test]
+    fn peer_list_empty() {
+        let encoded = encode_peer_list(&[]);
+        let decoded = decode_peer_list(&encoded);
+        assert!(decoded.is_empty());
+    }
+
+    #[test]
+    fn peer_list_truncated_data() {
+        // Only 1 byte — too short for count.
+        assert!(decode_peer_list(&[0]).is_empty());
+        // Count says 2 but only 1 peer present.
+        let mut data = vec![2, 0]; // count = 2
+        data.extend_from_slice(&[0xAA; 32]); // only 1 peer
+        let decoded = decode_peer_list(&data);
+        assert_eq!(decoded.len(), 1);
+    }
+
+    #[test]
+    fn dht_status_display() {
+        assert_eq!(format!("{}", DhtStatus::Bootstrapping), "Bootstrapping");
+        assert_eq!(format!("{}", DhtStatus::Ready), "Ready");
+        assert_eq!(format!("{}", DhtStatus::PublishFailed), "Failed");
+    }
+
+    #[test]
+    fn decode_peer_list_exact_boundary() {
+        // Build data with count=2 and exactly 2 + 32 + 32 = 66 bytes.
+        // Both peers should decode successfully.
+        let sk0 = iroh::SecretKey::generate(&mut rand::rng());
+        let sk1 = iroh::SecretKey::generate(&mut rand::rng());
+        let id0 = *sk0.public().as_bytes();
+        let id1 = *sk1.public().as_bytes();
+
+        let mut data = vec![2, 0]; // count = 2 (u16 LE)
+        data.extend_from_slice(&id0);
+        data.extend_from_slice(&id1);
+        assert_eq!(data.len(), 66);
+
+        let decoded = decode_peer_list(&data);
+        assert_eq!(decoded.len(), 2);
+        assert_eq!(*decoded[0].as_bytes(), id0);
+        assert_eq!(*decoded[1].as_bytes(), id1);
+    }
+
+    #[test]
+    fn decode_peer_list_one_byte_short() {
+        // Build data with count=2 but only 2 + 32 + 31 = 65 bytes.
+        // First peer decodes, second is truncated and skipped.
+        let sk0 = iroh::SecretKey::generate(&mut rand::rng());
+        let sk1 = iroh::SecretKey::generate(&mut rand::rng());
+        let id0 = *sk0.public().as_bytes();
+        let id1 = *sk1.public().as_bytes();
+
+        let mut data = vec![2, 0]; // count = 2 (u16 LE)
+        data.extend_from_slice(&id0);
+        data.extend_from_slice(&id1[..31]); // only 31 bytes of second peer
+        assert_eq!(data.len(), 65);
+
+        let decoded = decode_peer_list(&data);
+        assert_eq!(decoded.len(), 1);
+        assert_eq!(*decoded[0].as_bytes(), id0);
+    }
+
+    #[test]
+    fn decode_peer_list_count_header_only() {
+        // Data with exactly 2 bytes (count=0). Must not be rejected by the length check.
+        // Kills mutant: `data.len() < 2` → `data.len() <= 2`.
+        let data = [0u8, 0]; // count = 0
+        let decoded = decode_peer_list(&data);
+        assert!(decoded.is_empty());
+
+        // Data with 2 bytes but count=1 and no peer data — decodes 0 (truncated).
+        let data = [1u8, 0]; // count = 1 but no peer bytes
+        let decoded = decode_peer_list(&data);
+        assert!(decoded.is_empty());
+    }
+
+    mod proptests {
+        use super::*;
+        use proptest::prelude::*;
+
+        proptest! {
+            #[test]
+            fn peer_list_roundtrip_prop(count in 0usize..=30) {
+                let keys: Vec<[u8; 32]> = (0..count)
+                    .map(|_| *iroh::SecretKey::generate(&mut rand::rng()).public().as_bytes())
+                    .collect();
+                let encoded = encode_peer_list(&keys);
+                let decoded = decode_peer_list(&encoded);
+                let expected = count.min(MAX_DHT_PEERS);
+                prop_assert_eq!(decoded.len(), expected);
+            }
+        }
+    }
+}

src/lib.rs

@@ -0,0 +1,18 @@
+//! Peer-to-peer `LoRa` bridge connecting `DongLoRa` USB dongles across the internet.
+//!
+//! Uses iroh-gossip for swarm-based packet broadcast and mainline DHT for
+//! zero-configuration peer discovery. Nodes sharing a passphrase automatically
+//! discover each other and relay radio packets through a gossip swarm.
+
+pub mod config;
+pub mod gossip;
+pub mod packet;
+pub mod radio;
+pub mod rate_limit;
+pub mod router;
+pub mod setup;
+
+// TUI is public only so its types are visible to the binary; not intended for
+// external consumption.
+#[doc(hidden)]
+pub mod tui;

src/main.rs

@@ -1,25 +1,21 @@
-mod config;
+use donglora_bridge::{config, gossip, radio, rate_limit, router, setup, tui};
-mod network;
-mod packet;
-mod radio;
-mod router;
-mod tui;
 
-use std::collections::HashMap;
 use std::sync::Arc;
 use std::time::Instant;
 
 use anyhow::{Context, Result};
 use clap::{Parser, Subcommand};
+use iroh::SecretKey;
 use tokio::sync::mpsc;
 use tokio_util::sync::CancellationToken;
-use tracing::info;
+use tracing::{info, warn};
 
-use crate::network::{Network, PeerConfig};
+use crate::gossip::PassphraseKeys;
+use crate::rate_limit::RateLimiter;
 use crate::router::Stats;
 
 #[derive(Parser)]
-#[command(name = "donglora-bridge", about = "Peer-to-peer LoRa bridge using iroh")]
+#[command(name = "donglora-bridge", about = "LoRa gossip bridge using iroh")]
 struct Cli {
     /// Path to config file (default: ~/.config/donglora-bridge/config.toml)
     #[arg(long)]
@@ -35,13 +31,12 @@ struct Cli {
 
 #[derive(Subcommand)]
 enum Commands {
-    /// Print this bridge's NodeId and exit
+    /// Interactive configuration wizard
-    ShowId,
+    Config,
-    /// Generate an example config and print to stdout
-    GenerateConfig,
 }
 
 #[tokio::main]
+#[allow(clippy::too_many_lines)]
 async fn main() -> Result<()> {
     let cli = Cli::parse();
 
@@ -51,121 +46,67 @@ async fn main() -> Result<()> {
         None => config::config_path()?,
     };
 
-    // Load or create secret key.
+    // Config subcommand: run wizard with existing config as defaults.
-    // Secret key lives alongside the config file (same dir, .key extension).
+    if matches!(cli.command, Some(Commands::Config)) {
-    let key_path = config_path.with_extension("key");
+        let existing = if config_path.exists() { config::load_config(&config_path).ok() } else { None };
-    let secret_key = config::load_or_create_secret_key(&key_path)?;
+        return setup::run_wizard(&config_path, existing.as_ref());
-    let node_id = secret_key.public();
-    let node_id_str = node_id.to_string();
-
-    // Handle subcommands.
-    match cli.command {
-        Some(Commands::ShowId) => {
-            println!("{node_id_str}");
-            return Ok(());
-        }
-        Some(Commands::GenerateConfig) => {
-            print!("{}", config::generate_default_config(&node_id_str));
-            return Ok(());
-        }
-        None => {}
     }
 
-    // First-run: if config doesn't exist, generate it and exit.
+    // First-run: no config file → run wizard automatically.
     if !config_path.exists() {
-        config::write_default_config(&config_path, &node_id_str)?;
+        println!("  No config found. Let's set one up!\n");
-        println!("Generated config at {}", config_path.display());
+        return setup::run_wizard(&config_path, None);
-        println!("Your NodeId: {node_id_str}");
-        println!();
-        println!("Add peers to your config and run again!");
-        return Ok(());
     }
 
     // Load config.
-    let cfg = config::load_config(&config_path)
+    let cfg =
-        .with_context(|| format!("loading config from {}", config_path.display()))?;
+        config::load_config(&config_path).with_context(|| format!("loading config from {}", config_path.display()))?;
 
     // Set up logging.
-    if cli.log_only {
+    setup_logging(cli.log_only, &cfg);
-        tracing_subscriber::fmt()
-            .with_env_filter(
-                tracing_subscriber::EnvFilter::try_from_default_env()
-                    .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("info")),
-            )
-            .init();
-    } else {
-        // Log to file in TUI mode.
-        let log_path = cfg
-            .bridge
-            .log_file
-            .clone()
-            .unwrap_or_else(|| config::default_log_path().unwrap_or_else(|_| "/tmp/donglora-bridge.log".into()));
-        if let Some(parent) = log_path.parent() {
-            std::fs::create_dir_all(parent).ok();
-        }
-        let file_appender = tracing_appender::rolling::never(
-            log_path.parent().unwrap_or(std::path::Path::new("/tmp")),
-            log_path.file_name().unwrap_or(std::ffi::OsStr::new("donglora-bridge.log")),
-        );
-        tracing_subscriber::fmt()
-            .with_env_filter(
-                tracing_subscriber::EnvFilter::try_from_default_env()
-                    .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("info")),
-            )
-            .with_writer(file_appender)
-            .with_ansi(false)
-            .init();
-    }
 
-    info!("donglora-bridge starting, NodeId: {node_id_str}");
+    // Ephemeral identity — fresh keypair each launch.
+    let secret_key = SecretKey::generate(&mut rand::rng());
+    let node_id = secret_key.public();
+    info!("donglora-bridge starting, ephemeral id: {}", node_id.fmt_short());
 
     // Parse radio config.
     let radio_config = cfg.radio.to_radio_config()?;
-    let radio_config_str = radio::format_radio_config(&radio_config);
 
-    // Parse peer configs.
+    // Derive passphrase keys.
-    let mut peer_configs = Vec::new();
+    let keys = PassphraseKeys::derive(&cfg.bridge.passphrase);
-    let mut peer_names: HashMap<iroh::PublicKey, String> = HashMap::new();
+    info!("topic: {}", hex::encode(&keys.topic_id.as_bytes()[..8]));
-    for entry in &cfg.peers {
-        let pk = entry.public_key()?;
-        let name = entry.display_name();
-        peer_names.insert(pk, name.clone());
-        peer_configs.push(PeerConfig {
-            public_key: pk,
-            name,
-            addresses: entry.addresses.clone(),
-        });
-    }
 
-    if peer_configs.is_empty() && !cli.log_only {
+    // Create rate limiter.
-        println!("No peers configured. Add peers to {} and run again.", config_path.display());
+    let rate_limiter = RateLimiter::from_radio_config(
-        println!("Your NodeId: {node_id_str}");
+        radio_config.sf,
-        return Ok(());
+        radio_config.bw,
-    }
+        radio_config.cr,
+        radio_config.preamble_len,
+        cfg.bridge.rate_limit_pps,
+    );
+    info!("rate limiter: {:.1} pps", rate_limiter.rate_pps());
 
-    // Create network.
+    // Create gossip network.
-    let network = Arc::new(Network::new(secret_key, peer_configs).await?);
+    let (swarm, gossip_event_rx, gossip_frame_tx) = gossip::Gossip::new(secret_key, &keys).await?;
-    info!("iroh endpoint bound, id: {node_id_str}");
+    let swarm = Arc::new(swarm);
-
-    // Start network.
-    let (net_event_rx, net_send_tx) = network.start();
 
     // Start radio.
-    let (radio_event_rx, radio_tx) = radio::spawn(radio_config, cfg.radio.port.clone());
+    let (radio_event_rx, radio_tx) = radio::spawn(radio_config, cfg.radio.port.clone())?;
 
     // Stats + log channel + radio config watch.
     let stats = Arc::new(Stats::default());
     let (log_tx, log_rx) = mpsc::channel(512);
-    let (config_watch_tx, config_watch_rx) = tokio::sync::watch::channel(
+    let (config_watch_tx, config_watch_rx) = tokio::sync::watch::channel(router::RadioConfigInfo {
-        router::RadioConfigInfo {
+        active: radio_config,
-            config_str: radio_config_str,
+        requested: radio_config,
         source: radio::ConfigSource::Ours,
-        },
+        device: String::new(),
-    );
+        connected: false,
+    });
 
     // Cancellation.
     let cancel = CancellationToken::new();
-
     let start_time = Instant::now();
 
     // Spawn router.
@@ -174,18 +115,18 @@ async fn main() -> Result<()> {
     let router_our_id = node_id;
     let dedup_window = std::time::Duration::from_secs(cfg.bridge.dedup_window_secs);
     let tx_queue_size = cfg.bridge.tx_queue_size;
-    let router_peer_names = peer_names;
 
     tokio::spawn(async move {
         router::run(
             router_our_id,
             dedup_window,
             tx_queue_size,
-            router_peer_names,
+            radio_config,
+            rate_limiter,
             radio_event_rx,
             radio_tx,
-            net_event_rx,
+            gossip_event_rx,
-            net_send_tx,
+            gossip_frame_tx,
             &router_stats,
             log_tx,
             config_watch_tx,
@@ -194,41 +135,76 @@ async fn main() -> Result<()> {
         router_cancel.cancel();
     });
 
+    // Spawn a task that cancels on ctrl-c or SIGTERM.
+    {
+        let cancel = cancel.clone();
+        tokio::spawn(async move {
+            let sigterm = tokio::signal::unix::signal(tokio::signal::unix::SignalKind::terminate());
+            match sigterm {
+                Ok(mut sigterm) => {
+                    tokio::select! {
+                        _ = tokio::signal::ctrl_c() => info!("received SIGINT"),
+                        _ = sigterm.recv() => info!("received SIGTERM"),
+                    }
+                }
+                Err(e) => {
+                    warn!("failed to register SIGTERM handler: {e:#}");
+                    let _ = tokio::signal::ctrl_c().await;
+                    info!("received SIGINT");
+                }
+            }
+            cancel.cancel();
+        });
+    }
+
     // Run TUI or headless.
     if cli.log_only {
         info!("running in headless mode");
-        // Just wait for cancellation or ctrl-c.
+        cancel.cancelled().await;
-        tokio::select! {
-            () = cancel.cancelled() => {},
-            result = tokio::signal::ctrl_c() => {
-                if let Err(e) = result {
-                    tracing::error!("signal handler error: {e}");
-                }
-                info!("received ctrl-c, shutting down");
-            }
-        }
     } else {
-        // Run TUI (blocks until q or cancel).
+        let terminal = tui::run(config_watch_rx, swarm.clone(), stats, log_rx, cancel.clone(), start_time);
-        if let Err(e) = tui::run(
+
-            node_id,
+        cancel.cancel();
-            config_watch_rx,
+        swarm.shutdown().await;
-            network.clone(),
+        info!("donglora-bridge stopped");
-            stats,
+
-            log_rx,
+        if let Ok(mut term) = terminal {
-            cancel.clone(),
+            tui::restore_terminal(&mut term);
-            start_time,
-        )
-        .await
-        {
-            // Restore terminal before printing error.
-            eprintln!("TUI error: {e:#}");
-        }
         }
 
-    // Shutdown.
+        return Ok(());
-    cancel.cancel();
+    }
-    network.shutdown().await;
+
+    // Shutdown (headless path).
+    swarm.shutdown().await;
     info!("donglora-bridge stopped");
 
     Ok(())
 }
+
+fn setup_logging(log_only: bool, cfg: &config::Config) {
+    let env_filter = || {
+        tracing_subscriber::EnvFilter::try_from_default_env()
+            .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("info"))
+    };
+
+    if log_only {
+        tracing_subscriber::fmt().with_env_filter(env_filter()).init();
+    } else {
+        let log_path = cfg
+            .bridge
+            .log_file
+            .clone()
+            .unwrap_or_else(|| config::default_log_path().unwrap_or_else(|_| "/tmp/donglora-bridge.log".into()));
+        if let Some(parent) = log_path.parent()
+            && let Err(e) = std::fs::create_dir_all(parent)
+        {
+            eprintln!("warning: failed to create log directory {}: {e}", parent.display());
+        }
+        let file_appender = tracing_appender::rolling::never(
+            log_path.parent().unwrap_or_else(|| std::path::Path::new("/tmp")),
+            log_path.file_name().unwrap_or_else(|| std::ffi::OsStr::new("donglora-bridge.log")),
+        );
+        tracing_subscriber::fmt().with_env_filter(env_filter()).with_writer(file_appender).with_ansi(false).init();
+    }
+}

src/network.rs

@@ -1,411 +0,0 @@
-use std::collections::HashMap;
-use std::sync::Arc;
-use std::time::Instant;
-
-use anyhow::{Context, Result};
-use bytes::Bytes;
-use iroh::endpoint::Connection;
-use iroh::{Endpoint, PublicKey, SecretKey, endpoint::presets};
-use tokio::sync::{Mutex, mpsc};
-use tokio_util::sync::CancellationToken;
-use tracing::{debug, info, warn};
-
-use crate::packet::Envelope;
-
-/// ALPN protocol identifier for donglora-bridge.
-const ALPN: &[u8] = b"donglora-bridge/0";
-
-/// Info about a configured peer.
-#[derive(Debug, Clone)]
-pub struct PeerConfig {
-    pub public_key: PublicKey,
-    pub name: String,
-    pub addresses: Vec<String>,
-}
-
-/// Observable state of a peer connection.
-#[derive(Debug, Clone)]
-pub struct PeerState {
-    pub name: String,
-    pub public_key: PublicKey,
-    pub connected: bool,
-    pub last_seen: Option<Instant>,
-    pub packets_in: u64,
-    pub packets_out: u64,
-}
-
-/// Event from the network to the router.
-#[allow(dead_code)]
-pub enum NetworkEvent {
-    /// A packet received from an iroh peer.
-    Packet {
-        from: PublicKey,
-        envelope: Envelope,
-    },
-    /// A peer connected.
-    PeerConnected(PublicKey),
-    /// A peer disconnected.
-    PeerDisconnected(PublicKey),
-}
-
-/// Shared peer connection map.
-type PeerConnections = Arc<Mutex<HashMap<PublicKey, Connection>>>;
-
-/// Shared peer state map.
-type PeerStates = Arc<Mutex<HashMap<PublicKey, PeerState>>>;
-
-/// The network layer: manages the iroh endpoint and peer connections.
-pub struct Network {
-    endpoint: Endpoint,
-    peer_configs: Vec<PeerConfig>,
-    connections: PeerConnections,
-    states: PeerStates,
-    cancel: CancellationToken,
-}
-
-impl Network {
-    /// Create a new network layer with the given identity and peer configuration.
-    pub async fn new(secret_key: SecretKey, peer_configs: Vec<PeerConfig>) -> Result<Self> {
-        let endpoint = Endpoint::builder(presets::N0)
-            .secret_key(secret_key)
-            .alpns(vec![ALPN.to_vec()])
-            .bind()
-            .await
-            .context("binding iroh endpoint")?;
-
-        // Wait for relay connection before trying to reach peers.
-        info!("waiting for iroh relay connection...");
-        endpoint.online().await;
-        let addr = endpoint.addr();
-        info!("iroh online, addr: {addr:?}");
-
-        let states = Arc::new(Mutex::new(HashMap::new()));
-        {
-            let mut s = states.lock().await;
-            for pc in &peer_configs {
-                s.insert(
-                    pc.public_key,
-                    PeerState {
-                        name: pc.name.clone(),
-                        public_key: pc.public_key,
-                        connected: false,
-                        last_seen: None,
-                        packets_in: 0,
-                        packets_out: 0,
-                    },
-                );
-            }
-        }
-
-        Ok(Self {
-            endpoint,
-            peer_configs,
-            connections: Arc::new(Mutex::new(HashMap::new())),
-            states,
-            cancel: CancellationToken::new(),
-        })
-    }
-
-    /// Get a snapshot of all peer states.
-    pub async fn peer_states(&self) -> Vec<PeerState> {
-        self.states.lock().await.values().cloned().collect()
-    }
-
-    /// Start the network: spawn outbound connection tasks + inbound accept loop.
-    ///
-    /// Returns a receiver for network events and a sender for outbound envelopes.
-    pub fn start(
-        &self,
-    ) -> (mpsc::Receiver<NetworkEvent>, mpsc::Sender<(Envelope, Option<PublicKey>)>) {
-        let (event_tx, event_rx) = mpsc::channel::<NetworkEvent>(256);
-        let (send_tx, send_rx) = mpsc::channel::<(Envelope, Option<PublicKey>)>(256);
-
-        // Spawn outbound connection tasks for each configured peer.
-        for pc in &self.peer_configs {
-            let endpoint = self.endpoint.clone();
-            let pk = pc.public_key;
-            let addrs = pc.addresses.clone();
-            let connections = self.connections.clone();
-            let states = self.states.clone();
-            let event_tx = event_tx.clone();
-            let cancel = self.cancel.clone();
-
-            tokio::spawn(async move {
-                outbound_connection_loop(endpoint, pk, addrs, connections, states, event_tx, cancel).await;
-            });
-        }
-
-        // Spawn inbound accept loop.
-        {
-            let endpoint = self.endpoint.clone();
-            let connections = self.connections.clone();
-            let states = self.states.clone();
-            let event_tx = event_tx.clone();
-            let cancel = self.cancel.clone();
-            let known_peers: Vec<PublicKey> =
-                self.peer_configs.iter().map(|pc| pc.public_key).collect();
-
-            tokio::spawn(async move {
-                accept_loop(endpoint, known_peers, connections, states, event_tx, cancel).await;
-            });
-        }
-
-        // Spawn broadcast sender task.
-        {
-            let connections = self.connections.clone();
-            let states = self.states.clone();
-            let cancel = self.cancel.clone();
-
-            tokio::spawn(async move {
-                broadcast_loop(connections, states, send_rx, cancel).await;
-            });
-        }
-
-        (event_rx, send_tx)
-    }
-
-    /// Shut down the network layer.
-    pub async fn shutdown(&self) {
-        self.cancel.cancel();
-        self.endpoint.close().await;
-    }
-}
-
-/// Maintain a persistent outbound connection to a peer, reconnecting on failure.
-async fn outbound_connection_loop(
-    endpoint: Endpoint,
-    peer_key: PublicKey,
-    addresses: Vec<String>,
-    connections: PeerConnections,
-    states: PeerStates,
-    event_tx: mpsc::Sender<NetworkEvent>,
-    cancel: CancellationToken,
-) {
-    let mut backoff = std::time::Duration::from_secs(1);
-    let max_backoff = std::time::Duration::from_secs(30);
-
-    loop {
-        if cancel.is_cancelled() {
-            return;
-        }
-
-        // Skip if we already have a connection (e.g., from inbound accept).
-        {
-            let conns = connections.lock().await;
-            if let Some(c) = conns.get(&peer_key)
-                && c.stable_id() != 0
-            {
-                // Connection exists and looks alive — wait and retry check.
-                drop(conns);
-                tokio::select! {
-                    () = cancel.cancelled() => return,
-                    () = tokio::time::sleep(std::time::Duration::from_secs(5)) => continue,
-                }
-            }
-        }
-
-        info!("connecting to peer {}", fmt_key(&peer_key));
-        let mut addr = iroh::EndpointAddr::new(peer_key);
-        // Add our relay URL as a hint — the peer is likely on the same relay network.
-        for relay_url in endpoint.addr().relay_urls() {
-            addr = addr.with_relay_url(relay_url.clone());
-        }
-        for a in &addresses {
-            if let Ok(sock) = a.parse::<std::net::SocketAddr>() {
-                addr = addr.with_ip_addr(sock);
-            }
-        }
-        debug!("connect addr: {addr:?}");
-        match endpoint.connect(addr, ALPN).await {
-            Ok(conn) => {
-                backoff = std::time::Duration::from_secs(1);
-                let remote = conn.remote_id();
-                info!("connected to peer {}", fmt_key(&remote));
-
-                {
-                    let mut conns = connections.lock().await;
-                    conns.insert(remote, conn.clone());
-                }
-                update_peer_connected(&states, &remote, true).await;
-                let _ = event_tx.send(NetworkEvent::PeerConnected(remote)).await;
-
-                // Read datagrams from this connection.
-                read_datagrams(conn, remote, connections.clone(), states.clone(), event_tx.clone(), cancel.clone()).await;
-
-                update_peer_connected(&states, &remote, false).await;
-                let _ = event_tx
-                    .send(NetworkEvent::PeerDisconnected(remote))
-                    .await;
-            }
-            Err(e) => {
-                warn!("connect to {} failed: {e:#}", fmt_key(&peer_key));
-            }
-        }
-
-        tokio::select! {
-            () = cancel.cancelled() => return,
-            () = tokio::time::sleep(backoff) => {},
-        }
-        backoff = (backoff * 2).min(max_backoff);
-    }
-}
-
-/// Accept inbound connections from known peers.
-async fn accept_loop(
-    endpoint: Endpoint,
-    known_peers: Vec<PublicKey>,
-    connections: PeerConnections,
-    states: PeerStates,
-    event_tx: mpsc::Sender<NetworkEvent>,
-    cancel: CancellationToken,
-) {
-    loop {
-        let incoming = tokio::select! {
-            () = cancel.cancelled() => return,
-            inc = endpoint.accept() => match inc {
-                Some(i) => i,
-                None => return,
-            },
-        };
-
-        let conn = match incoming.await {
-            Ok(c) => c,
-            Err(e) => {
-                warn!("inbound connection failed: {e:#}");
-                continue;
-            }
-        };
-
-        let remote = conn.remote_id();
-        if !known_peers.contains(&remote) {
-            warn!("rejecting unknown peer {}", fmt_key(&remote));
-            conn.close(0u32.into(), b"unknown peer");
-            continue;
-        }
-
-        info!("accepted connection from peer {}", fmt_key(&remote));
-        {
-            let mut conns = connections.lock().await;
-            conns.insert(remote, conn.clone());
-        }
-        update_peer_connected(&states, &remote, true).await;
-        let _ = event_tx.send(NetworkEvent::PeerConnected(remote)).await;
-
-        // Spawn a reader for this inbound connection.
-        let conns = connections.clone();
-        let sts = states.clone();
-        let etx = event_tx.clone();
-        let ct = cancel.clone();
-        tokio::spawn(async move {
-            read_datagrams(conn, remote, conns.clone(), sts.clone(), etx.clone(), ct).await;
-            update_peer_connected(&sts, &remote, false).await;
-            let _ = etx.send(NetworkEvent::PeerDisconnected(remote)).await;
-        });
-    }
-}
-
-/// Read datagrams from a connection until it closes.
-async fn read_datagrams(
-    conn: Connection,
-    remote: PublicKey,
-    connections: PeerConnections,
-    states: PeerStates,
-    event_tx: mpsc::Sender<NetworkEvent>,
-    cancel: CancellationToken,
-) {
-    loop {
-        let data = tokio::select! {
-            () = cancel.cancelled() => break,
-            result = conn.read_datagram() => match result {
-                Ok(d) => d,
-                Err(e) => {
-                    debug!("datagram read from {} ended: {e}", fmt_key(&remote));
-                    break;
-                }
-            },
-        };
-
-        if let Some(envelope) = Envelope::decode(&data) {
-            {
-                let mut sts = states.lock().await;
-                if let Some(ps) = sts.get_mut(&remote) {
-                    ps.packets_in += 1;
-                    ps.last_seen = Some(Instant::now());
-                }
-            }
-            let _ = event_tx
-                .send(NetworkEvent::Packet {
-                    from: remote,
-                    envelope,
-                })
-                .await;
-        } else {
-            warn!("malformed envelope from {}", fmt_key(&remote));
-        }
-    }
-
-    // Clean up connection.
-    let mut conns = connections.lock().await;
-    if let Some(existing) = conns.get(&remote)
-        && existing.stable_id() == conn.stable_id()
-    {
-        conns.remove(&remote);
-    }
-}
-
-/// Broadcast envelopes to all connected peers (except the optional skip key).
-async fn broadcast_loop(
-    connections: PeerConnections,
-    states: PeerStates,
-    mut send_rx: mpsc::Receiver<(Envelope, Option<PublicKey>)>,
-    cancel: CancellationToken,
-) {
-    loop {
-        let (envelope, skip) = tokio::select! {
-            () = cancel.cancelled() => return,
-            msg = send_rx.recv() => match msg {
-                Some(m) => m,
-                None => return,
-            },
-        };
-
-        let data = Bytes::from(envelope.encode());
-        let conns = connections.lock().await;
-
-        for (pk, conn) in conns.iter() {
-            if Some(*pk) == skip {
-                continue;
-            }
-            match conn.send_datagram(data.clone()) {
-                Ok(()) => {
-                    let mut sts = states.lock().await;
-                    if let Some(ps) = sts.get_mut(pk) {
-                        ps.packets_out += 1;
-                    }
-                }
-                Err(e) => {
-                    debug!("send to {} failed: {e}", fmt_key(pk));
-                }
-            }
-        }
-    }
-}
-
-async fn update_peer_connected(states: &PeerStates, pk: &PublicKey, connected: bool) {
-    let mut sts = states.lock().await;
-    if let Some(ps) = sts.get_mut(pk) {
-        ps.connected = connected;
-        if connected {
-            ps.last_seen = Some(Instant::now());
-        }
-    }
-}
-
-fn fmt_key(pk: &PublicKey) -> String {
-    let s = pk.to_string();
-    if s.len() > 12 {
-        format!("{}...", &s[..12])
-    } else {
-        s
-    }
-}

src/packet.rs

@@ -1,12 +1,12 @@
-use iroh::PublicKey;
+//! Wire format definitions for radio packets and gossip frames.
+//!
+//! Includes SNR quality grading against `LoRa` demodulation floors and blake3
+//! content hashing for deduplication.
 
-/// Wire protocol version.
+/// Gossip frame header size: `sender(32) + rssi(2) + snr(2) + payload_len(2) = 38`
-const VERSION: u8 = 0;
+const FRAME_HEADER_SIZE: usize = 38;
 
-/// Envelope header size: version(1) + origin(32) + seq(8) + rssi(2) + snr(2) + payload_len(2) = 47
+/// SNR quality grade for a received `LoRa` packet.
-const HEADER_SIZE: usize = 47;
-
-/// SNR quality grade for a received LoRa packet.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Grade {
     /// SNR well above demodulation floor (margin >= 3 dB).
@@ -21,7 +21,8 @@ pub enum Grade {
 
 impl Grade {
     /// Returns true if the packet is reliable enough to forward.
-    pub fn should_forward(self) -> bool {
+    #[must_use]
+    pub const fn should_forward(self) -> bool {
         matches!(self, Self::Good | Self::Marginal)
     }
 }
@@ -38,7 +39,8 @@ impl std::fmt::Display for Grade {
 }
 
 /// Grade a received packet's SNR against the demodulation floor for the given
-/// spreading factor. See PROTOCOL.md for the formula.
+/// spreading factor.
+#[must_use]
 pub fn snr_grade(snr: i16, sf: u8) -> Grade {
     if !(-32..=32).contains(&snr) {
         return Grade::Invalid;
@@ -54,7 +56,7 @@ pub fn snr_grade(snr: i16, sf: u8) -> Grade {
     }
 }
 
-/// A packet received from the radio, before wrapping in an envelope.
+/// A packet received from the radio, before wrapping in a gossip frame.
 #[derive(Debug, Clone)]
 pub struct RadioPacket {
     pub rssi: i16,
@@ -62,72 +64,67 @@ pub struct RadioPacket {
     pub payload: Vec<u8>,
 }
 
-/// A bridge envelope — the wire format sent between iroh peers.
+/// A gossip frame — the wire format sent through the iroh-gossip swarm.
+///
+/// Wire format: `[sender: 32B] [rssi: i16 LE] [snr: i16 LE] [payload_len: u16 LE] [payload: NB]`
 #[derive(Debug, Clone)]
-pub struct Envelope {
+pub struct GossipFrame {
-    /// NodeId of the bridge that first heard this packet on radio.
+    /// `EndpointId` (`PublicKey` bytes) of the bridge that first heard this packet on radio.
-    pub origin: PublicKey,
+    pub sender: [u8; 32],
-    /// Per-origin sequence number (monotonically increasing).
-    pub seq: u64,
     /// RSSI at the originating bridge (informational).
     pub rssi: i16,
     /// SNR at the originating bridge (informational).
     pub snr: i16,
-    /// Raw LoRa payload.
+    /// Raw `LoRa` payload.
     pub payload: Vec<u8>,
 }
 
-impl Envelope {
+impl GossipFrame {
-    /// Encode this envelope into bytes for sending as a QUIC datagram.
+    /// Create a new gossip frame from a public key and radio packet data.
+    #[must_use]
+    pub fn new(sender: &iroh::PublicKey, rssi: i16, snr: i16, payload: Vec<u8>) -> Self {
+        Self { sender: *sender.as_bytes(), rssi, snr, payload }
+    }
+
+    /// Encode this frame into bytes for gossip broadcast.
+    #[must_use]
     pub fn encode(&self) -> Vec<u8> {
-        let mut buf = Vec::with_capacity(HEADER_SIZE + self.payload.len());
+        let mut buf = Vec::with_capacity(FRAME_HEADER_SIZE + self.payload.len());
-        buf.push(VERSION);
+        buf.extend_from_slice(&self.sender);
-        buf.extend_from_slice(self.origin.as_bytes());
-        buf.extend_from_slice(&self.seq.to_le_bytes());
         buf.extend_from_slice(&self.rssi.to_le_bytes());
         buf.extend_from_slice(&self.snr.to_le_bytes());
+        #[allow(clippy::cast_possible_truncation)] // LoRa payloads never exceed 256 bytes
         let len = self.payload.len() as u16;
         buf.extend_from_slice(&len.to_le_bytes());
         buf.extend_from_slice(&self.payload);
         buf
     }
 
-    /// Decode an envelope from bytes received as a QUIC datagram.
+    /// Decode a gossip frame from bytes received from the swarm.
+    #[must_use]
     pub fn decode(data: &[u8]) -> Option<Self> {
-        if data.len() < HEADER_SIZE {
+        if data.len() < FRAME_HEADER_SIZE {
             return None;
         }
-        if data[0] != VERSION {
+        let sender: [u8; 32] = data[..32].try_into().ok()?;
+        let rssi = i16::from_le_bytes(data[32..34].try_into().ok()?);
+        let snr = i16::from_le_bytes(data[34..36].try_into().ok()?);
+        let payload_len = u16::from_le_bytes(data[36..38].try_into().ok()?) as usize;
+        if data.len() != FRAME_HEADER_SIZE + payload_len {
             return None;
         }
-        let origin = PublicKey::from_bytes(data[1..33].try_into().ok()?).ok()?;
+        Some(Self { sender, rssi, snr, payload: data[FRAME_HEADER_SIZE..].to_vec() })
-        let seq = u64::from_le_bytes(data[33..41].try_into().ok()?);
-        let rssi = i16::from_le_bytes(data[41..43].try_into().ok()?);
-        let snr = i16::from_le_bytes(data[43..45].try_into().ok()?);
-        let payload_len = u16::from_le_bytes(data[45..47].try_into().ok()?) as usize;
-        if data.len() != HEADER_SIZE + payload_len {
-            return None;
-        }
-        Some(Self {
-            origin,
-            seq,
-            rssi,
-            snr,
-            payload: data[HEADER_SIZE..].to_vec(),
-        })
     }
 }
 
-/// Compute a 16-byte content hash for deduplication.
+/// Compute a 32-byte blake3 content hash for deduplication.
-pub fn content_hash(payload: &[u8]) -> [u8; 16] {
+#[must_use]
-    let hash = blake3::hash(payload);
+pub fn content_hash(payload: &[u8]) -> [u8; 32] {
-    let bytes = hash.as_bytes();
+    *blake3::hash(payload).as_bytes()
-    let mut out = [0u8; 16];
-    out.copy_from_slice(&bytes[..16]);
-    out
 }
 
 #[cfg(test)]
+#[allow(clippy::unwrap_used, clippy::expect_used)]
 mod tests {
     use super::*;
 
@@ -146,34 +143,76 @@ mod tests {
     }
 
     #[test]
-    fn envelope_roundtrip() {
+    fn gossip_frame_roundtrip() {
         let key = iroh::SecretKey::generate(&mut rand::rng());
-        let env = Envelope {
+        let frame = GossipFrame::new(&key.public(), -85, 8, vec![1, 2, 3, 4, 5]);
-            origin: key.public(),
+        let encoded = frame.encode();
-            seq: 42,
+        let decoded = GossipFrame::decode(&encoded).expect("decode should succeed");
-            rssi: -85,
+        assert_eq!(decoded.sender, *key.public().as_bytes());
-            snr: 8,
+        assert_eq!(decoded.rssi, -85);
-            payload: vec![1, 2, 3, 4, 5],
+        assert_eq!(decoded.snr, 8);
-        };
+        assert_eq!(decoded.payload, vec![1, 2, 3, 4, 5]);
-        let encoded = env.encode();
-        let decoded = Envelope::decode(&encoded).unwrap();
-        assert_eq!(decoded.origin, env.origin);
-        assert_eq!(decoded.seq, env.seq);
-        assert_eq!(decoded.rssi, env.rssi);
-        assert_eq!(decoded.snr, env.snr);
-        assert_eq!(decoded.payload, env.payload);
     }
 
     #[test]
-    fn envelope_reject_short() {
+    fn gossip_frame_reject_short() {
-        assert!(Envelope::decode(&[0u8; 10]).is_none());
+        assert!(GossipFrame::decode(&[0u8; 10]).is_none());
     }
 
     #[test]
-    fn envelope_reject_bad_version() {
+    fn gossip_frame_decode_empty_payload() {
-        let mut data = vec![1u8]; // version 1
+        // Exactly FRAME_HEADER_SIZE (38) bytes with payload_len=0 must decode.
-        data.extend_from_slice(&[0u8; 46]);
+        // Kills mutant: `data.len() < 38` → `data.len() <= 38`.
-        assert!(Envelope::decode(&data).is_none());
+        let mut data = vec![0u8; 38];
+        data[36..38].copy_from_slice(&0u16.to_le_bytes()); // payload_len = 0
+        let frame = GossipFrame::decode(&data);
+        assert!(frame.is_some(), "38-byte frame with 0-length payload must decode");
+        assert!(frame.unwrap().payload.is_empty());
+    }
+
+    #[test]
+    fn gossip_frame_reject_wrong_length() {
+        // Header says payload_len=5 but only 3 bytes follow.
+        let mut data = vec![0u8; 38 + 3];
+        data[36..38].copy_from_slice(&5u16.to_le_bytes());
+        assert!(GossipFrame::decode(&data).is_none());
+    }
+
+    #[test]
+    fn should_forward_true_for_good_and_marginal() {
+        assert!(Grade::Good.should_forward());
+        assert!(Grade::Marginal.should_forward());
+    }
+
+    #[test]
+    fn should_forward_false_for_unreliable_and_invalid() {
+        assert!(!Grade::Unreliable.should_forward());
+        assert!(!Grade::Invalid.should_forward());
+    }
+
+    #[test]
+    fn grade_display() {
+        assert_eq!(format!("{}", Grade::Good), "GOOD");
+        assert_eq!(format!("{}", Grade::Marginal), "MARG");
+        assert_eq!(format!("{}", Grade::Unreliable), "UNRL");
+        assert_eq!(format!("{}", Grade::Invalid), "INVL");
+    }
+
+    #[test]
+    fn snr_grade_exact_boundaries() {
+        // SF12: min_snr = -2.5 * (12 - 4) = -20.0
+        //
+        // At snr=-20, margin = -20 - (-20.0) = 0.0 exactly.
+        // The code uses `margin < 0.0`, so 0.0 is NOT < 0.0 → Marginal (not Unreliable).
+        assert_eq!(snr_grade(-20, 12), Grade::Marginal);
+        // One below: snr=-21, margin = -1.0 → Unreliable.
+        assert_eq!(snr_grade(-21, 12), Grade::Unreliable);
+
+        // At snr=-17, margin = -17 - (-20.0) = 3.0 exactly.
+        // The code uses `margin < 3.0`, so 3.0 is NOT < 3.0 → Good (not Marginal).
+        assert_eq!(snr_grade(-17, 12), Grade::Good);
+        // One below: snr=-18, margin = 2.0 → Marginal.
+        assert_eq!(snr_grade(-18, 12), Grade::Marginal);
     }
 
     #[test]
@@ -184,4 +223,36 @@ mod tests {
         let h3 = content_hash(b"world");
         assert_ne!(h1, h3);
     }
+
+    mod proptests {
+        use super::*;
+        use proptest::prelude::*;
+
+        proptest! {
+            #[test]
+            fn gossip_frame_roundtrip_prop(
+                rssi in -200i16..=200i16,
+                snr in -32i16..=32i16,
+                payload in proptest::collection::vec(any::<u8>(), 0..256),
+            ) {
+                let key = iroh::SecretKey::generate(&mut rand::rng());
+                let frame = GossipFrame::new(&key.public(), rssi, snr, payload.clone());
+                let encoded = frame.encode();
+                let decoded = GossipFrame::decode(&encoded).unwrap();
+                prop_assert_eq!(decoded.rssi, rssi);
+                prop_assert_eq!(decoded.snr, snr);
+                prop_assert_eq!(decoded.payload, payload);
+            }
+
+            #[test]
+            fn content_hash_deterministic_prop(data in proptest::collection::vec(any::<u8>(), 0..1024)) {
+                prop_assert_eq!(content_hash(&data), content_hash(&data));
+            }
+
+            #[test]
+            fn snr_grade_never_panics(snr in i16::MIN..=i16::MAX, sf in 5u8..=12u8) {
+                let _ = snr_grade(snr, sf);
+            }
+        }
+    }
 }

src/radio.rs

@@ -1,6 +1,11 @@
+//! `DongLoRa` hardware communication on a blocking thread.
+//!
+//! Handles connection, config negotiation, RX/TX, liveness pings, and
+//! exponential backoff reconnection.
+
 use std::time::Duration;
 
-use anyhow::Result;
+use anyhow::{Context, Result};
 use donglora_client::{RadioConfig, Response, Transport};
 use tokio::sync::mpsc;
 use tracing::{debug, error, info, warn};
@@ -20,8 +25,8 @@ pub enum ConfigSource {
 pub enum RadioEvent {
     /// A valid packet received from the radio (already SNR-filtered).
     Packet(RadioPacket),
-    /// Radio connected (or reconnected) with the active config.
+    /// Radio connected (or reconnected) with the active config and device info.
-    Connected(RadioConfig, ConfigSource),
+    Connected(RadioConfig, ConfigSource, String),
     /// Radio disconnected — attempting reconnect.
     Disconnected,
 }
@@ -29,40 +34,46 @@ pub enum RadioEvent {
 /// Spawn the blocking radio thread.
 ///
 /// Returns a receiver for radio events and a sender for TX payloads.
-pub fn spawn(
+pub fn spawn(config: RadioConfig, port: Option<String>) -> Result<(mpsc::Receiver<RadioEvent>, mpsc::Sender<Vec<u8>>)> {
-    config: RadioConfig,
-    port: Option<String>,
-) -> (mpsc::Receiver<RadioEvent>, mpsc::Sender<Vec<u8>>) {
     let (event_tx, event_rx) = mpsc::channel::<RadioEvent>(256);
     let (tx_send, tx_recv) = mpsc::channel::<Vec<u8>>(64);
 
     std::thread::Builder::new()
         .name("radio".into())
         .spawn(move || radio_loop(config, port, event_tx, tx_recv))
-        .ok();
+        .context("failed to spawn radio thread")?;
 
-    (event_rx, tx_send)
+    Ok((event_rx, tx_send))
 }
 
+#[allow(clippy::needless_pass_by_value)] // values moved across thread boundary in spawn()
 fn radio_loop(
     config: RadioConfig,
     port: Option<String>,
     event_tx: mpsc::Sender<RadioEvent>,
     mut tx_recv: mpsc::Receiver<Vec<u8>>,
 ) {
-    let mut backoff = Duration::from_secs(1);
+    let initial_backoff = Duration::from_millis(250);
-    let max_backoff = Duration::from_secs(30);
+    let max_backoff = Duration::from_secs(5);
+    let mut backoff = initial_backoff;
 
     loop {
-        match connect_and_run(&config, &port, &event_tx, &mut tx_recv) {
+        let started = std::time::Instant::now();
+        match connect_and_run(&config, port.as_deref(), &event_tx, &mut tx_recv) {
             Ok(()) => {
-                // Clean shutdown (channel closed).
                 info!("radio thread exiting");
                 return;
             }
             Err(e) => {
                 error!("radio error: {e:#}");
                 let _ = event_tx.blocking_send(RadioEvent::Disconnected);
+
+                // If we were connected for a while, reset backoff so
+                // the next reconnect attempt is fast.
+                if started.elapsed() > Duration::from_secs(5) {
+                    backoff = initial_backoff;
+                }
+
                 info!("reconnecting in {backoff:?}");
                 std::thread::sleep(backoff);
                 backoff = (backoff * 2).min(max_backoff);
@@ -73,55 +84,69 @@ fn radio_loop(
 
 fn connect_and_run(
     config: &RadioConfig,
-    port: &Option<String>,
+    port: Option<&str>,
     event_tx: &mpsc::Sender<RadioEvent>,
     tx_recv: &mut mpsc::Receiver<Vec<u8>>,
 ) -> Result<()> {
-    let timeout = Duration::from_secs(2);
+    // Long initial timeout: the mux serializes commands through the dongle,
+    // so our `GetConfig` might have to wait behind other clients' commands.
+    let timeout = Duration::from_secs(10);
 
     info!("connecting to dongle...");
-    let mut client = if let Some(port) = &port {
+    let (mut client, device) = if let Some(port) = port {
-        donglora_client::connect(Some(port), timeout)?
+        let c = donglora_client::connect(Some(port), timeout)?;
+        (c, shorten_path(port))
+    } else if let Ok(c) = donglora_client::connect_mux_auto(timeout) {
+        (c, "mux".to_string())
     } else {
-        donglora_client::connect_default()?
+        let port_path = donglora_client::find_port()
+            .ok_or_else(|| anyhow::anyhow!("no mux or USB dongle found"))?;
+        info!("no mux found, connecting to serial port {port_path}");
+        let c = donglora_client::connect(Some(&port_path), timeout)?;
+        (c, shorten_path(&port_path))
     };
+    info!("[radio] transport connected: {device}");
 
-    client.ping()?;
+    info!("[radio] sending ping...");
-    info!("dongle connected, configuring radio");
+    match client.ping() {
+        Ok(()) => info!("[radio] ping OK"),
+        Err(e) => {
+            info!("[radio] ping FAILED: {e:#}");
+            return Err(e);
+        }
+    }
 
-    // Try to set our config. If the mux rejects it (config already locked by
+    info!("[radio] negotiating config...");
-    // another client), fall back to reading whatever config is active.
+    let (active_config, config_source) = match negotiate_config(&mut client, config, &device) {
-    let (active_config, config_source) = match client.set_config(*config) {
+        Ok(result) => {
-        Ok(()) => {
+            info!("[radio] config negotiated: source={:?}, config={}", result.1, format_radio_config(&result.0));
-            info!("radio configured with our settings");
+            result
-            (*config, ConfigSource::Ours)
         }
         Err(e) => {
-            warn!("SetConfig failed ({e:#}), reading active config from mux");
+            info!("[radio] config negotiation FAILED: {e:#}");
-            match client.get_config() {
+            return Err(e);
-                Ok(mux_config) => {
-                    info!(
-                        "using mux config: {}",
-                        format_radio_config(&mux_config)
-                    );
-                    (mux_config, ConfigSource::Mux)
-                }
-                Err(e2) => {
-                    anyhow::bail!("SetConfig failed ({e:#}) and GetConfig also failed ({e2:#})");
-                }
-            }
         }
     };
 
-    client.start_rx()?;
+    info!("[radio] sending start_rx...");
-    info!("radio receiving");
+    match client.start_rx() {
+        Ok(()) => info!("[radio] start_rx OK"),
+        Err(e) => {
+            info!("[radio] start_rx FAILED: {e:#}");
+            return Err(e);
+        }
+    }
 
-    let _ = event_tx.blocking_send(RadioEvent::Connected(active_config, config_source));
+    let _ = event_tx.blocking_send(RadioEvent::Connected(active_config, config_source, device));
 
     // Set a short timeout so we can interleave RX and TX.
-    client
+    client.transport_mut().set_timeout(Duration::from_millis(100))?;
-        .transport_mut()
+    info!("[radio] entering main loop");
-        .set_timeout(Duration::from_millis(100))?;
+
+    // Liveness: ping the mux periodically when idle to detect a dead connection.
+    // Without this, a killed mux causes recv() to silently return Ok(None) forever.
+    let liveness_interval = Duration::from_secs(2);
+    let mut last_activity = std::time::Instant::now();
 
     loop {
         // Check for TX requests (non-blocking).
@@ -129,72 +154,129 @@ fn connect_and_run(
             debug!("TX {} bytes", payload.len());
             if let Err(e) = client.transmit(&payload, None) {
                 warn!("transmit error: {e:#}");
+                return Err(e);
             }
+            last_activity = std::time::Instant::now();
         }
 
         // Check for RX packets.
         match client.recv() {
             Ok(Some(Response::RxPacket { rssi, snr, payload })) => {
+                last_activity = std::time::Instant::now();
                 let grade = snr_grade(snr, active_config.sf);
                 if grade.should_forward() {
-                    debug!(
+                    debug!("RX {} bytes rssi={rssi} snr={snr} grade={grade}", payload.len());
-                        "RX {} bytes rssi={rssi} snr={snr} grade={grade}",
-                        payload.len()
-                    );
                     let pkt = RadioPacket { rssi, snr, payload };
                     if event_tx.blocking_send(RadioEvent::Packet(pkt)).is_err() {
-                        // Router dropped — shut down.
                         return Ok(());
                     }
                 } else {
-                    debug!(
+                    debug!("RX drop {} bytes rssi={rssi} snr={snr} grade={grade}", payload.len());
-                        "RX drop {} bytes rssi={rssi} snr={snr} grade={grade}",
-                        payload.len()
-                    );
                 }
             }
             Ok(Some(_)) => {
-                // Non-RxPacket unsolicited response — ignore.
+                last_activity = std::time::Instant::now();
-            }
-            Ok(None) => {
-                // Timeout — no packet, loop back to check TX.
-            }
-            Err(e) if is_timeout_error(&e) => {
-                // Mux sockets return WouldBlock on timeout instead of Ok(0).
-                // Treat the same as Ok(None) — just a timeout, not a real error.
             }
+            Ok(None) => {}
+            Err(e) if is_timeout_error(&e) => {}
             Err(e) => return Err(e),
         }
 
-        // If the event channel is closed, the router is gone — exit cleanly.
+        // Liveness check: if no real activity for a while, ping the mux.
+        if last_activity.elapsed() >= liveness_interval {
+            // Temporarily extend the timeout for the ping command.
+            let _ = client.transport_mut().set_timeout(Duration::from_secs(2));
+            match client.ping() {
+                Ok(()) => {
+                    last_activity = std::time::Instant::now();
+                }
+                Err(e) => {
+                    warn!("liveness ping failed: {e:#}");
+                    return Err(e);
+                }
+            }
+            // Restore the short timeout.
+            let _ = client.transport_mut().set_timeout(Duration::from_millis(100));
+        }
+
         if event_tx.is_closed() {
             return Ok(());
         }
     }
 }
 
-/// Check if an anyhow::Error wraps a timeout-like I/O error.
+/// Negotiate radio config with the dongle/mux.
 ///
-/// Workaround: donglora-client's `read_frame` handles `TimedOut` but not
+/// Strategy:
-/// `WouldBlock`. On Linux, socket read timeouts return EAGAIN (WouldBlock),
+/// 1. `GetConfig` first to read what's active.
-/// not TimedOut. Serial ports return Ok(0) so they work fine, but mux
+/// 2. If it matches our desired config, use it — no `SetConfig` needed.
-/// sockets surface this as an error. We catch it here instead of letting
+/// 3. If it differs and we're on the mux, accept the mux's config.
-/// it trigger the reconnect loop.
+/// 4. If it differs and we're on direct serial, `SetConfig` to push ours.
-fn is_timeout_error(e: &anyhow::Error) -> bool {
+/// 5. If `GetConfig` fails, try `SetConfig` with our desired config.
-    if let Some(io_err) = e.downcast_ref::<std::io::Error>() {
+fn negotiate_config<T: Transport>(
-        matches!(
+    client: &mut donglora_client::Client<T>,
-            io_err.kind(),
+    desired: &RadioConfig,
-            std::io::ErrorKind::WouldBlock | std::io::ErrorKind::TimedOut
+    device: &str,
-        )
+) -> Result<(RadioConfig, ConfigSource)> {
+    info!("[negotiate] get_config...");
+    match client.get_config() {
+        Ok(cfg) => {
+            if configs_match(&cfg, desired) {
+                info!("[negotiate] get_config OK (matches desired): {}", format_radio_config(&cfg));
+                Ok((cfg, ConfigSource::Ours))
+            } else if device == "mux" {
+                info!("[negotiate] get_config OK (mux config differs, accepting): {}", format_radio_config(&cfg));
+                Ok((cfg, ConfigSource::Mux))
             } else {
-        false
+                info!("[negotiate] get_config OK (serial config differs, setting ours)");
+                client.set_config(*desired)?;
+                info!("[negotiate] set_config OK");
+                Ok((*desired, ConfigSource::Ours))
+            }
+        }
+        Err(e) => {
+            info!("[negotiate] get_config FAILED: {e:#}");
+            // No config on radio — try to set ours.
+            info!("[negotiate] trying set_config...");
+            match client.set_config(*desired) {
+                Ok(()) => {
+                    info!("[negotiate] set_config OK");
+                    Ok((*desired, ConfigSource::Ours))
+                }
+                Err(e2) => {
+                    info!("[negotiate] set_config FAILED: {e2:#}");
+                    anyhow::bail!("GetConfig failed ({e:#}) and SetConfig also failed ({e2:#})");
+                }
+            }
+        }
     }
 }
 
-/// Format a RadioConfig for display.
+/// Shorten a device path to just the filename for display.
-pub fn format_radio_config(config: &RadioConfig) -> String {
+fn shorten_path(path: &str) -> String {
-    let freq_mhz = config.freq_hz as f64 / 1_000_000.0;
+    std::path::Path::new(path).file_name().map_or_else(|| path.to_string(), |f| f.to_string_lossy().into_owned())
-    let bw = match config.bw {
+}
+
+fn configs_match(a: &RadioConfig, b: &RadioConfig) -> bool {
+    a.freq_hz == b.freq_hz
+        && a.bw == b.bw
+        && a.sf == b.sf
+        && a.cr == b.cr
+        && a.sync_word == b.sync_word
+        && a.tx_power_dbm == b.tx_power_dbm
+        && a.preamble_len == b.preamble_len
+        && a.cad == b.cad
+}
+
+fn is_timeout_error(e: &anyhow::Error) -> bool {
+    e.downcast_ref::<std::io::Error>()
+        .is_some_and(|io_err| matches!(io_err.kind(), std::io::ErrorKind::WouldBlock | std::io::ErrorKind::TimedOut))
+}
+
+/// Format a bandwidth value for display.
+#[must_use]
+pub const fn format_bandwidth(bw: donglora_client::Bandwidth) -> &'static str {
+    match bw {
         donglora_client::Bandwidth::Khz7 => "7.8 kHz",
         donglora_client::Bandwidth::Khz10 => "10.4 kHz",
         donglora_client::Bandwidth::Khz15 => "15.6 kHz",
@@ -205,20 +287,159 @@ pub fn format_radio_config(config: &RadioConfig) -> String {
         donglora_client::Bandwidth::Khz125 => "125 kHz",
         donglora_client::Bandwidth::Khz250 => "250 kHz",
         donglora_client::Bandwidth::Khz500 => "500 kHz",
-    };
+    }
+}
+
+/// Format a `RadioConfig` for display.
+#[must_use]
+pub fn format_radio_config(config: &RadioConfig) -> String {
+    let freq_mhz = f64::from(config.freq_hz) / 1_000_000.0;
+    let bw = format_bandwidth(config.bw);
     let power = if config.tx_power_dbm == donglora_client::TX_POWER_MAX {
         "max".to_string()
     } else {
         format!("{} dBm", config.tx_power_dbm)
     };
-    let preamble = if config.preamble_len == 0 {
+    let preamble = if config.preamble_len == 0 { 16 } else { config.preamble_len };
-        16
-    } else {
-        config.preamble_len
-    };
     let cad = if config.cad != 0 { "on" } else { "off" };
     format!(
         "{freq_mhz:.3}MHz SF{} BW{bw} CR4/{} SW0x{:04X} TX:{power} Pre:{preamble} CAD:{cad}",
         config.sf, config.cr, config.sync_word
     )
 }
+
+#[cfg(test)]
+#[allow(clippy::unwrap_used, clippy::expect_used)]
+mod tests {
+    use super::*;
+
+    fn default_config() -> RadioConfig {
+        RadioConfig {
+            freq_hz: 910_525_000,
+            bw: donglora_client::Bandwidth::Khz62,
+            sf: 7,
+            cr: 5,
+            sync_word: 0x3444,
+            tx_power_dbm: 22,
+            preamble_len: 16,
+            cad: 1,
+        }
+    }
+
+    #[test]
+    fn configs_match_identical() {
+        let a = default_config();
+        let b = default_config();
+        assert!(configs_match(&a, &b));
+    }
+
+    #[test]
+    fn configs_match_differs_each_field() {
+        let base = default_config();
+
+        let mut c = base;
+        c.freq_hz = 915_000_000;
+        assert!(!configs_match(&base, &c));
+
+        let mut c = base;
+        c.sf = 12;
+        assert!(!configs_match(&base, &c));
+
+        let mut c = base;
+        c.cr = 8;
+        assert!(!configs_match(&base, &c));
+
+        let mut c = base;
+        c.sync_word = 0x1234;
+        assert!(!configs_match(&base, &c));
+
+        let mut c = base;
+        c.tx_power_dbm = 10;
+        assert!(!configs_match(&base, &c));
+
+        let mut c = base;
+        c.preamble_len = 8;
+        assert!(!configs_match(&base, &c));
+
+        let mut c = base;
+        c.cad = 0;
+        assert!(!configs_match(&base, &c));
+    }
+
+    #[test]
+    fn is_timeout_would_block() {
+        let e = anyhow::Error::from(std::io::Error::new(std::io::ErrorKind::WouldBlock, "test"));
+        assert!(is_timeout_error(&e));
+    }
+
+    #[test]
+    fn is_timeout_timed_out() {
+        let e = anyhow::Error::from(std::io::Error::new(std::io::ErrorKind::TimedOut, "test"));
+        assert!(is_timeout_error(&e));
+    }
+
+    #[test]
+    fn is_timeout_false_for_other() {
+        let e = anyhow::Error::from(std::io::Error::new(std::io::ErrorKind::ConnectionReset, "test"));
+        assert!(!is_timeout_error(&e));
+    }
+
+    #[test]
+    fn shorten_path_extracts_filename() {
+        assert_eq!(shorten_path("/dev/ttyACM0"), "ttyACM0");
+        assert_eq!(shorten_path("ttyACM0"), "ttyACM0");
+    }
+
+    #[test]
+    fn format_bandwidth_all_variants() {
+        assert_eq!(format_bandwidth(donglora_client::Bandwidth::Khz7), "7.8 kHz");
+        assert_eq!(format_bandwidth(donglora_client::Bandwidth::Khz125), "125 kHz");
+        assert_eq!(format_bandwidth(donglora_client::Bandwidth::Khz500), "500 kHz");
+    }
+
+    #[test]
+    fn format_radio_config_typical() {
+        let cfg = default_config();
+        let s = format_radio_config(&cfg);
+        assert!(s.contains("910.525MHz"));
+        assert!(s.contains("SF7"));
+        assert!(s.contains("CR4/5"));
+        assert!(s.contains("0x3444"));
+        assert!(s.contains("CAD:on"), "cad=1 should show CAD:on: {s}");
+    }
+
+    #[test]
+    fn format_radio_config_cad_off() {
+        let mut cfg = default_config();
+        cfg.cad = 0;
+        let s = format_radio_config(&cfg);
+        assert!(s.contains("CAD:off"), "cad=0 should show CAD:off: {s}");
+    }
+
+    #[test]
+    fn format_radio_config_max_power() {
+        let mut cfg = default_config();
+        cfg.tx_power_dbm = donglora_client::TX_POWER_MAX;
+        let s = format_radio_config(&cfg);
+        assert!(s.contains("TX:max"));
+        assert!(!s.contains("dBm"), "max power should not contain 'dBm': {s}");
+    }
+
+    #[test]
+    fn format_radio_config_non_max_power() {
+        let mut cfg = default_config();
+        cfg.tx_power_dbm = 22;
+        assert_ne!(cfg.tx_power_dbm, donglora_client::TX_POWER_MAX);
+        let s = format_radio_config(&cfg);
+        assert!(s.contains("22 dBm"), "non-max power should contain '22 dBm': {s}");
+        assert!(!s.contains("max"), "non-max power should not contain 'max': {s}");
+    }
+
+    #[test]
+    fn format_radio_config_zero_preamble() {
+        let mut cfg = default_config();
+        cfg.preamble_len = 0;
+        let s = format_radio_config(&cfg);
+        assert!(s.contains("Pre:16"));
+    }
+}

src/rate_limit.rs

@@ -0,0 +1,343 @@
+//! `LoRa` air-time-aware token bucket rate limiter.
+//!
+//! Calculates transmit rate from the Semtech `LoRa` air time formula and
+//! enforces it with a configurable burst allowance.
+
+use std::time::{Duration, Instant};
+
+use donglora_client::Bandwidth;
+
+/// Token-bucket rate limiter for radio transmissions.
+///
+/// Calculates a safe transmit rate from the `LoRa` radio configuration (spreading factor,
+/// bandwidth, coding rate) and enforces it with a token bucket that allows short bursts.
+pub struct RateLimiter {
+    tokens: f64,
+    max_tokens: f64,
+    refill_rate: f64, // tokens per second
+    last_refill: Instant,
+}
+
+/// Default burst size (max tokens). Allows short bursts of 3 back-to-back packets
+/// to handle bursty mesh traffic without triggering rate limiting on every packet.
+const DEFAULT_BURST: f64 = 3.0;
+
+/// Reference payload size (bytes) used to estimate air time for rate calculation.
+/// 50 bytes is a representative `MeshCore` packet size (header + small payload).
+const REFERENCE_PAYLOAD_BYTES: usize = 50;
+
+/// Target duty cycle fraction. 50% leaves headroom for other radio traffic sharing
+/// the channel while still forwarding bridge traffic aggressively.
+const TARGET_DUTY_CYCLE: f64 = 0.5;
+
+impl RateLimiter {
+    /// Create a rate limiter derived from radio config.
+    ///
+    /// If `override_pps` is `Some`, use that rate directly instead of calculating.
+    #[must_use]
+    pub fn from_radio_config(sf: u8, bw: Bandwidth, cr: u8, preamble: u16, override_pps: Option<f64>) -> Self {
+        let refill_rate = override_pps.map_or_else(
+            || {
+                let air_time = lora_air_time(REFERENCE_PAYLOAD_BYTES, sf, bw, cr, preamble);
+                let secs = air_time.as_secs_f64();
+                if secs > 0.0 { TARGET_DUTY_CYCLE / secs } else { 10.0 }
+            },
+            |pps| pps.max(0.01),
+        );
+        Self { tokens: DEFAULT_BURST, max_tokens: DEFAULT_BURST, refill_rate, last_refill: Instant::now() }
+    }
+
+    /// Try to consume one token. Returns `true` if the transmission is allowed.
+    pub fn try_acquire(&mut self) -> bool {
+        self.refill();
+        if self.tokens >= 1.0 {
+            self.tokens -= 1.0;
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Current rate in packets per second.
+    #[must_use]
+    pub const fn rate_pps(&self) -> f64 {
+        self.refill_rate
+    }
+
+    fn refill(&mut self) {
+        let now = Instant::now();
+        let elapsed = now.duration_since(self.last_refill).as_secs_f64();
+        self.tokens = elapsed.mul_add(self.refill_rate, self.tokens).min(self.max_tokens);
+        self.last_refill = now;
+    }
+}
+
+/// Estimate `LoRa` packet air time using the Semtech `LoRa` time-on-air formula.
+///
+/// Parameters:
+/// - `payload_bytes`: payload size in bytes
+/// - `sf`: spreading factor (7–12)
+/// - `bw`: bandwidth
+/// - `cr`: coding rate denominator (5–8, meaning 4/5 to 4/8)
+/// - `preamble`: preamble length in symbols (0 = firmware default of 16)
+#[must_use]
+pub fn lora_air_time(payload_bytes: usize, sf: u8, bw: Bandwidth, cr: u8, preamble: u16) -> Duration {
+    let sf_f = f64::from(sf);
+    let bw_hz = bandwidth_hz(bw);
+    let preamble_symbols = if preamble == 0 { 16.0 } else { f64::from(preamble) };
+
+    // Symbol time in seconds.
+    let t_sym = sf_f.exp2() / bw_hz;
+
+    // Preamble time.
+    let t_preamble = (preamble_symbols + 4.25) * t_sym;
+
+    // Low data rate optimize: enabled when SF >= 11 and BW <= 125 kHz.
+    let de: f64 = if sf >= 11 && bw_hz <= 125_000.0 { 1.0 } else { 0.0 };
+
+    // Payload symbol count (Semtech formula with CRC enabled, explicit header).
+    #[allow(clippy::cast_precision_loss)] // payload_bytes is always < 256
+    let payload_f = payload_bytes as f64;
+    let numerator = 8.0f64.mul_add(payload_f, (-4.0f64).mul_add(sf_f, 44.0));
+    let denominator = 4.0f64.mul_add(sf_f, -8.0 * de);
+    let n_payload = (numerator / denominator).ceil().max(0.0).mul_add(f64::from(cr), 8.0);
+
+    let t_payload = n_payload * t_sym;
+    let total = t_preamble + t_payload;
+
+    Duration::from_secs_f64(total)
+}
+
+const fn bandwidth_hz(bw: Bandwidth) -> f64 {
+    match bw {
+        Bandwidth::Khz7 => 7_800.0,
+        Bandwidth::Khz10 => 10_400.0,
+        Bandwidth::Khz15 => 15_600.0,
+        Bandwidth::Khz20 => 20_800.0,
+        Bandwidth::Khz31 => 31_250.0,
+        Bandwidth::Khz41 => 41_700.0,
+        Bandwidth::Khz62 => 62_500.0,
+        Bandwidth::Khz125 => 125_000.0,
+        Bandwidth::Khz250 => 250_000.0,
+        Bandwidth::Khz500 => 500_000.0,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn air_time_sf7_bw125() {
+        let t = lora_air_time(50, 7, Bandwidth::Khz125, 5, 16);
+        // SF7/125kHz/CR4/5/16-preamble/50 bytes: ~100ms range
+        assert!(t.as_millis() > 50, "air time too short: {t:?}");
+        assert!(t.as_millis() < 300, "air time too long: {t:?}");
+    }
+
+    #[test]
+    fn air_time_sf12_bw125() {
+        let t = lora_air_time(50, 12, Bandwidth::Khz125, 5, 16);
+        // SF12/125kHz: should be multiple seconds
+        assert!(t.as_secs() >= 1, "air time too short: {t:?}");
+        assert!(t.as_secs() < 10, "air time too long: {t:?}");
+    }
+
+    #[test]
+    fn rate_limiter_allows_burst() {
+        let mut rl = RateLimiter::from_radio_config(7, Bandwidth::Khz125, 5, 16, None);
+        // Should allow burst of 3
+        assert!(rl.try_acquire());
+        assert!(rl.try_acquire());
+        assert!(rl.try_acquire());
+        // 4th should fail (no time for refill)
+        assert!(!rl.try_acquire());
+    }
+
+    #[test]
+    fn rate_limiter_override() {
+        let rl = RateLimiter::from_radio_config(7, Bandwidth::Khz125, 5, 16, Some(42.0));
+        assert!((rl.rate_pps() - 42.0).abs() < f64::EPSILON);
+    }
+
+    #[test]
+    fn air_time_zero_preamble_uses_default() {
+        let t_default = lora_air_time(50, 7, Bandwidth::Khz125, 5, 0);
+        let t_explicit = lora_air_time(50, 7, Bandwidth::Khz125, 5, 16);
+        assert_eq!(t_default, t_explicit);
+    }
+
+    // ── Mutant-killing tests for from_radio_config (items 1-5) ────────
+
+    #[test]
+    fn from_radio_config_calculates_reasonable_rate() {
+        // SF7/BW125/CR5/preamble16 with 50-byte reference payload:
+        // air time ~105.7ms, so rate = 0.5 / 0.1057 ~= 4.73 pps.
+        let rl = RateLimiter::from_radio_config(7, Bandwidth::Khz125, 5, 16, None);
+        let rate = rl.rate_pps();
+        // Must be between 0.1 and 100 (rules out fallback of 10.0 indirectly,
+        // and catches if secs<=0 path is taken or division is wrong).
+        assert!(rate > 0.1, "rate too low: {rate}");
+        assert!(rate < 100.0, "rate too high: {rate}");
+        // Specifically verify it is NOT the 10.0 fallback, proving secs > 0.0 was true.
+        assert!((rate - 10.0).abs() > 0.5, "rate should not be the 10.0 fallback: {rate}");
+        // Tight check around the expected ~4.73 pps.
+        assert!(rate > 4.0, "rate should be near 4.73: {rate}");
+        assert!(rate < 5.5, "rate should be near 4.73: {rate}");
+    }
+
+    #[test]
+    fn from_radio_config_sf12_rate_much_slower() {
+        // SF12/BW125: air time ~2564ms, rate = 0.5 / 2.564 ~= 0.195 pps.
+        let rl = RateLimiter::from_radio_config(12, Bandwidth::Khz125, 5, 16, None);
+        let rate = rl.rate_pps();
+        assert!(rate > 0.1, "rate too low: {rate}");
+        assert!(rate < 0.5, "rate too high: {rate}");
+        // Definitely not 10.0 fallback.
+        assert!((rate - 10.0).abs() > 1.0, "rate should not be the fallback: {rate}");
+    }
+
+    // ── Mutant-killing tests for refill (item 6) ───────────────────
+
+    #[test]
+    fn rate_limiter_refills_after_waiting() {
+        // Use override_pps for predictable timing: 10 pps = 1 token per 100ms.
+        let mut rl = RateLimiter::from_radio_config(7, Bandwidth::Khz125, 5, 16, Some(10.0));
+        // Exhaust all burst tokens.
+        assert!(rl.try_acquire());
+        assert!(rl.try_acquire());
+        assert!(rl.try_acquire());
+        assert!(!rl.try_acquire(), "burst should be exhausted");
+
+        // Sleep enough for at least 1 token to refill (10 pps -> 100ms per token).
+        std::thread::sleep(Duration::from_millis(200));
+
+        // After sleeping, refill should have added tokens, so acquire succeeds.
+        assert!(rl.try_acquire(), "should succeed after refill");
+    }
+
+    // ── Mutant-killing tests for lora_air_time (items 7-14) ────────
+
+    #[test]
+    fn air_time_exact_sf7_bw125() {
+        // SF7, BW125kHz, CR4/5, preamble=16, payload=50 bytes.
+        // Expected: 105.728 ms (computed from Semtech formula).
+        let t = lora_air_time(50, 7, Bandwidth::Khz125, 5, 16);
+        let ms = t.as_secs_f64() * 1000.0;
+        assert!((ms - 105.728).abs() < 0.01, "SF7/BW125 air time should be ~105.728ms, got {ms:.3}ms");
+    }
+
+    #[test]
+    fn air_time_exact_sf12_bw125() {
+        // SF12, BW125kHz, CR4/5, preamble=16, payload=50 bytes.
+        // Expected: 2564.096 ms.
+        let t = lora_air_time(50, 12, Bandwidth::Khz125, 5, 16);
+        let ms = t.as_secs_f64() * 1000.0;
+        assert!((ms - 2564.096).abs() < 0.01, "SF12/BW125 air time should be ~2564.096ms, got {ms:.3}ms");
+    }
+
+    #[test]
+    fn air_time_ldro_sf11_bw125_vs_sf10_bw125() {
+        // SF>=11 && BW<=125kHz triggers LDRO. SF10 does not.
+        // SF11/BW125: 1445.888 ms (de=1), SF10/BW125: 681.984 ms (de=0).
+        let t11 = lora_air_time(50, 11, Bandwidth::Khz125, 5, 16);
+        let t10 = lora_air_time(50, 10, Bandwidth::Khz125, 5, 16);
+
+        let ms11 = t11.as_secs_f64() * 1000.0;
+        let ms10 = t10.as_secs_f64() * 1000.0;
+
+        // Verify exact values.
+        assert!((ms11 - 1445.888).abs() < 0.01, "SF11/BW125 should be ~1445.888ms, got {ms11:.3}ms");
+        assert!((ms10 - 681.984).abs() < 0.01, "SF10/BW125 should be ~681.984ms, got {ms10:.3}ms");
+
+        // SF11 must be more than double SF10 due to LDRO + SF increase.
+        // (Kills mutant: replace >= with < in sf >= 11 check.)
+        assert!(t11 > t10 * 2, "SF11 with LDRO should be >2x SF10");
+    }
+
+    #[test]
+    fn air_time_ldro_not_triggered_high_bw() {
+        // SF11/BW250: LDRO should NOT be active (BW > 125kHz).
+        // Expected: 641.024 ms (de=0).
+        let t11_250 = lora_air_time(50, 11, Bandwidth::Khz250, 5, 16);
+        let ms = t11_250.as_secs_f64() * 1000.0;
+        assert!((ms - 641.024).abs() < 0.01, "SF11/BW250 should be ~641.024ms (no LDRO), got {ms:.3}ms");
+
+        // Compare with SF11/BW125 which HAS LDRO.
+        let t11_125 = lora_air_time(50, 11, Bandwidth::Khz125, 5, 16);
+        // Even accounting for halved BW doubling the base time, the LDRO effect
+        // on SF11/BW125 makes it much longer than simply 2x SF11/BW250.
+        assert!(t11_125 > t11_250 * 2, "SF11/BW125 (LDRO on) should be >2x SF11/BW250 (LDRO off)");
+    }
+
+    #[test]
+    fn air_time_preamble_scaling() {
+        // Changing preamble by N symbols changes air time by N * t_sym.
+        // t_sym for SF7/BW125 = 2^7 / 125000 = 1.024 ms.
+        let t8 = lora_air_time(50, 7, Bandwidth::Khz125, 5, 8);
+        let t16 = lora_air_time(50, 7, Bandwidth::Khz125, 5, 16);
+        let t32 = lora_air_time(50, 7, Bandwidth::Khz125, 5, 32);
+
+        let diff_8_to_16 = t16.as_secs_f64() - t8.as_secs_f64();
+        let diff_16_to_32 = t32.as_secs_f64() - t16.as_secs_f64();
+
+        let t_sym = 128.0 / 125_000.0; // 1.024 ms
+
+        // 8 -> 16: 8 symbols difference.
+        let expected_8 = 8.0f64.mul_add(t_sym, -diff_8_to_16).abs();
+        assert!(expected_8 < 1e-9, "preamble 8->16 should add 8*t_sym, got {diff_8_to_16:.6}s");
+
+        // 16 -> 32: 16 symbols difference.
+        let expected_16 = 16.0f64.mul_add(t_sym, -diff_16_to_32).abs();
+        assert!(expected_16 < 1e-9, "preamble 16->32 should add 16*t_sym, got {diff_16_to_32:.6}s");
+    }
+
+    #[test]
+    fn air_time_sensible_range_all_sf_bw() {
+        // Verify reasonable bounds for all SF/BW combos with 50-byte payload.
+        // This catches gross formula errors (e.g. division replaced with modulo).
+        let bandwidths = [
+            Bandwidth::Khz7,
+            Bandwidth::Khz10,
+            Bandwidth::Khz15,
+            Bandwidth::Khz20,
+            Bandwidth::Khz31,
+            Bandwidth::Khz41,
+            Bandwidth::Khz62,
+            Bandwidth::Khz125,
+            Bandwidth::Khz250,
+            Bandwidth::Khz500,
+        ];
+        for sf in 7..=12u8 {
+            for &bw in &bandwidths {
+                let t = lora_air_time(50, sf, bw, 5, 16);
+                let ms = t.as_secs_f64() * 1000.0;
+                // Fastest: SF7/BW500 ~26ms. Slowest: SF12/BW7.8kHz ~many seconds.
+                // All should be > 1ms and < 300s.
+                assert!(ms > 1.0, "SF{sf}/BW{bw:?}: air time too short: {ms:.3}ms");
+                assert!(ms < 300_000.0, "SF{sf}/BW{bw:?}: air time too long: {ms:.3}ms");
+            }
+        }
+    }
+
+    mod proptests {
+        use super::*;
+        use proptest::prelude::*;
+
+        proptest! {
+            #[test]
+            fn air_time_always_positive(
+                payload in 0usize..256,
+                sf in 7u8..=12u8,
+                cr in 5u8..=8u8,
+                preamble in 0u16..=64u16,
+            ) {
+                for bw in [Bandwidth::Khz7, Bandwidth::Khz62, Bandwidth::Khz125, Bandwidth::Khz500] {
+                    let t = lora_air_time(payload, sf, bw, cr, preamble);
+                    prop_assert!(t > Duration::ZERO, "air time must be positive");
+                    prop_assert!(t < Duration::from_secs(600), "air time should be < 600s");
+                }
+            }
+        }
+    }
+}

src/router.rs

@@ -1,3 +1,8 @@
+//! Central packet bus bridging radio and gossip swarm.
+//!
+//! Applies blake3 content-hash deduplication, token bucket rate limiting,
+//! and TX queue management.
+
 use std::collections::{HashMap, VecDeque};
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::time::{Duration, Instant};
@@ -6,61 +11,62 @@ use iroh::PublicKey;
 use tokio::sync::mpsc;
 use tracing::{debug, warn};
 
-use crate::network::NetworkEvent;
+use crate::gossip::GossipEvent;
-use crate::packet::{Envelope, RadioPacket, content_hash};
+use crate::packet::{GossipFrame, content_hash};
-use crate::radio::{ConfigSource, RadioEvent, format_radio_config};
+use crate::radio::{ConfigSource, RadioEvent};
+use crate::rate_limit::RateLimiter;
 
 /// Active radio config info, sent to the TUI via watch channel.
 #[derive(Debug, Clone)]
 pub struct RadioConfigInfo {
-    pub config_str: String,
+    pub active: donglora_client::RadioConfig,
+    pub requested: donglora_client::RadioConfig,
     pub source: ConfigSource,
+    pub device: String,
+    pub connected: bool,
 }
 
 /// Packet event for the TUI log.
 #[derive(Debug, Clone)]
 pub struct PacketLogEntry {
     pub timestamp: Instant,
+    pub hash: [u8; 32],
     pub direction: PacketDirection,
     pub size: usize,
     pub snr: Option<i16>,
     pub rssi: Option<i16>,
-    pub peer_name: Option<String>,
     pub action: PacketAction,
 }
 
+/// Which side the packet arrived from.
 #[derive(Debug, Clone, Copy)]
 pub enum PacketDirection {
-    RadioRx,
+    /// Heard on local radio → forwarded to gossip swarm.
-    RadioTx,
+    RadioIn,
-    NetRx,
+    /// Received from gossip swarm → queued for radio TX.
+    GossipIn,
 }
 
+/// What happened to the packet.
 #[derive(Debug, Clone, Copy)]
 pub enum PacketAction {
-    Forwarded,
+    /// Successfully bridged (radio→gossip or gossip→radio).
-    Transmitted,
+    Bridged,
+    /// Dropped: duplicate payload.
     DroppedDedup,
+    /// Dropped: TX queue full.
     DroppedQueueFull,
-}
+    /// Dropped: rate limiter.
-
+    DroppedRateLimit,
-impl std::fmt::Display for PacketDirection {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Self::RadioRx => write!(f, "RX "),
-            Self::RadioTx => write!(f, "TX "),
-            Self::NetRx => write!(f, "NET"),
-        }
-    }
 }
 
 impl std::fmt::Display for PacketAction {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            Self::Forwarded => write!(f, "FWD"),
+            Self::Bridged => write!(f, ""),
-            Self::Transmitted => write!(f, "TX"),
             Self::DroppedDedup => write!(f, "DUP"),
             Self::DroppedQueueFull => write!(f, "FULL"),
+            Self::DroppedRateLimit => write!(f, "RATE"),
         }
     }
 }
@@ -70,146 +76,230 @@ impl std::fmt::Display for PacketAction {
 pub struct Stats {
     pub radio_rx: AtomicU64,
     pub radio_tx: AtomicU64,
-    pub forwarded: AtomicU64,
+    pub gossip_rx: AtomicU64,
-    pub dropped_snr: AtomicU64,
+    pub gossip_tx: AtomicU64,
-    pub dropped_dedup: AtomicU64,
+    pub dedup_hits: AtomicU64,
+    pub rate_limit_drops: AtomicU64,
     pub dropped_queue: AtomicU64,
+    pub neighbor_count: AtomicU64,
     pub radio_connected: AtomicU64, // 0 = disconnected, 1 = connected
 }
 
 impl Stats {
+    #[must_use]
     pub fn snapshot(&self) -> StatsSnapshot {
         StatsSnapshot {
             radio_rx: self.radio_rx.load(Ordering::Relaxed),
             radio_tx: self.radio_tx.load(Ordering::Relaxed),
-            forwarded: self.forwarded.load(Ordering::Relaxed),
+            gossip_rx: self.gossip_rx.load(Ordering::Relaxed),
-            dropped_snr: self.dropped_snr.load(Ordering::Relaxed),
+            gossip_tx: self.gossip_tx.load(Ordering::Relaxed),
-            dropped_dedup: self.dropped_dedup.load(Ordering::Relaxed),
+            dedup_hits: self.dedup_hits.load(Ordering::Relaxed),
+            rate_limit_drops: self.rate_limit_drops.load(Ordering::Relaxed),
             dropped_queue: self.dropped_queue.load(Ordering::Relaxed),
+            neighbor_count: self.neighbor_count.load(Ordering::Relaxed),
             radio_connected: self.radio_connected.load(Ordering::Relaxed) != 0,
         }
     }
 }
 
+/// Point-in-time snapshot of bridge statistics, cloned from atomic counters.
 #[derive(Debug, Clone)]
 pub struct StatsSnapshot {
     pub radio_rx: u64,
     pub radio_tx: u64,
-    pub forwarded: u64,
+    pub gossip_rx: u64,
-    pub dropped_snr: u64,
+    pub gossip_tx: u64,
-    pub dropped_dedup: u64,
+    pub dedup_hits: u64,
+    pub rate_limit_drops: u64,
     pub dropped_queue: u64,
+    pub neighbor_count: u64,
     pub radio_connected: bool,
 }
 
 /// Time-bounded dedup cache.
-struct DedupCache<K: std::hash::Hash + Eq> {
+struct DedupCache {
-    entries: HashMap<K, Instant>,
+    entries: HashMap<[u8; 32], Instant>,
     ttl: Duration,
 }
 
-impl<K: std::hash::Hash + Eq> DedupCache<K> {
+impl DedupCache {
     fn new(ttl: Duration) -> Self {
-        Self {
+        Self { entries: HashMap::new(), ttl }
-            entries: HashMap::new(),
-            ttl,
-        }
     }
 
     /// Returns true if the key was already present (i.e., duplicate).
-    fn check_and_insert(&mut self, key: K) -> bool {
+    fn check_and_insert(&mut self, key: [u8; 32]) -> bool {
         let now = Instant::now();
-        self.prune(now);
+        if let Some(ts) = self.entries.get(&key)
-        if self.entries.contains_key(&key) {
+            && now.duration_since(*ts) < self.ttl
+        {
             return true;
         }
         self.entries.insert(key, now);
         false
     }
 
-    fn insert(&mut self, key: K) {
+    fn prune(&mut self) {
-        self.entries.insert(key, Instant::now());
+        let now = Instant::now();
-    }
-
-    fn prune(&mut self, now: Instant) {
         self.entries.retain(|_, ts| now.duration_since(*ts) < self.ttl);
     }
 }
 
-/// Peer name lookup for log entries.
-struct PeerNames {
-    names: HashMap<PublicKey, String>,
-}
-
-impl PeerNames {
-    fn get(&self, pk: &PublicKey) -> Option<String> {
-        self.names.get(pk).cloned()
-    }
-}
-
 /// Run the router — the central packet bus.
 ///
-/// This is an async task that mediates between the radio thread, the iroh
+/// Bridges radio packets to/from the gossip swarm with deduplication and rate limiting.
-/// network layer, and the TUI.
+#[allow(clippy::too_many_arguments, clippy::too_many_lines)]
-#[allow(clippy::too_many_arguments)]
 pub async fn run(
     our_id: PublicKey,
     dedup_window: Duration,
     tx_queue_size: usize,
-    peer_names: HashMap<PublicKey, String>,
+    requested_radio_config: donglora_client::RadioConfig,
+    mut rate_limiter: RateLimiter,
     mut radio_rx: mpsc::Receiver<RadioEvent>,
     radio_tx: mpsc::Sender<Vec<u8>>,
-    mut net_rx: mpsc::Receiver<NetworkEvent>,
+    mut gossip_rx: mpsc::Receiver<GossipEvent>,
-    net_tx: mpsc::Sender<(Envelope, Option<PublicKey>)>,
+    gossip_tx: mpsc::Sender<GossipFrame>,
     stats: &Stats,
     log_tx: mpsc::Sender<PacketLogEntry>,
     config_tx: tokio::sync::watch::Sender<RadioConfigInfo>,
 ) {
-    let names = PeerNames { names: peer_names };
+    let mut dedup = DedupCache::new(dedup_window);
-    let mut seq: u64 = 0;
-    let mut iroh_dedup: DedupCache<(PublicKey, u64)> = DedupCache::new(dedup_window);
-    let mut echo_dedup: DedupCache<[u8; 16]> = DedupCache::new(dedup_window);
     let mut tx_queue: VecDeque<Vec<u8>> = VecDeque::with_capacity(tx_queue_size);
+    let mut last_cleanup = Instant::now();
+    let cleanup_interval = Duration::from_secs(30);
 
     loop {
+        // Periodic dedup cleanup.
+        if last_cleanup.elapsed() >= cleanup_interval {
+            dedup.prune();
+            last_cleanup = Instant::now();
+        }
+
         tokio::select! {
             // Radio events.
             event = radio_rx.recv() => {
                 let Some(event) = event else { break };
                 match event {
                     RadioEvent::Packet(pkt) => {
-                        handle_radio_packet(
+                        stats.radio_rx.fetch_add(1, Ordering::Relaxed);
-                            &our_id, &mut seq, &pkt,
+
-                            &mut echo_dedup, &net_tx,
+                        let hash = content_hash(&pkt.payload);
-                            stats, &log_tx, &names,
+                        if dedup.check_and_insert(hash) {
-                        ).await;
+                            stats.dedup_hits.fetch_add(1, Ordering::Relaxed);
+                            debug!("radio RX dedup suppressed ({} bytes)", pkt.payload.len());
+                            let _ = log_tx.send(PacketLogEntry {
+                                timestamp: Instant::now(),
+                                hash,
+                                direction: PacketDirection::RadioIn,
+                                size: pkt.payload.len(),
+                                snr: Some(pkt.snr),
+                                rssi: Some(pkt.rssi),
+                                action: PacketAction::DroppedDedup,
+                            }).await;
+                            continue;
                         }
-                    RadioEvent::Connected(active_config, source) => {
+
+                        // Wrap and broadcast to gossip.
+                        let frame = GossipFrame::new(&our_id, pkt.rssi, pkt.snr, pkt.payload.clone());
+                        stats.gossip_tx.fetch_add(1, Ordering::Relaxed);
+                        let _ = gossip_tx.send(frame).await;
+
+                        let _ = log_tx.send(PacketLogEntry {
+                            timestamp: Instant::now(),
+                            hash,
+                            direction: PacketDirection::RadioIn,
+                            size: pkt.payload.len(),
+                            snr: Some(pkt.snr),
+                            rssi: Some(pkt.rssi),
+                            action: PacketAction::Bridged,
+                        }).await;
+                    }
+                    RadioEvent::Connected(active_config, source, device) => {
                         stats.radio_connected.store(1, Ordering::Relaxed);
                         let _ = config_tx.send(RadioConfigInfo {
-                            config_str: format_radio_config(&active_config),
+                            active: active_config,
+                            requested: requested_radio_config,
                             source,
+                            device,
+                            connected: true,
                         });
                     }
                     RadioEvent::Disconnected => {
                         stats.radio_connected.store(0, Ordering::Relaxed);
+                        config_tx.send_modify(|info| info.connected = false);
                     }
                 }
             }
 
-            // Network events.
+            // Gossip events.
-            event = net_rx.recv() => {
+            event = gossip_rx.recv() => {
                 let Some(event) = event else { break };
                 match event {
-                    NetworkEvent::Packet { from, envelope } => {
+                    GossipEvent::Frame(frame) => {
-                        handle_net_packet(
+                        stats.gossip_rx.fetch_add(1, Ordering::Relaxed);
-                            &from, envelope, &mut iroh_dedup, &mut echo_dedup,
+
-                            &mut tx_queue, tx_queue_size,
+                        let hash = content_hash(&frame.payload);
-                            stats, &log_tx, &names,
+                        if dedup.check_and_insert(hash) {
-                        ).await;
+                            stats.dedup_hits.fetch_add(1, Ordering::Relaxed);
+                            debug!("gossip RX dedup suppressed ({} bytes)", frame.payload.len());
+                            let _ = log_tx.send(PacketLogEntry {
+                                timestamp: Instant::now(),
+                                hash,
+                                direction: PacketDirection::GossipIn,
+                                size: frame.payload.len(),
+                                snr: Some(frame.snr),
+                                rssi: Some(frame.rssi),
+                                action: PacketAction::DroppedDedup,
+                            }).await;
+                            continue;
                         }
-                    NetworkEvent::PeerConnected(_) | NetworkEvent::PeerDisconnected(_) => {
+
-                        // State tracked in network layer; TUI reads from there.
+                        // Rate limit check.
+                        if !rate_limiter.try_acquire() {
+                            stats.rate_limit_drops.fetch_add(1, Ordering::Relaxed);
+                            debug!("rate limited ({} bytes)", frame.payload.len());
+                            let _ = log_tx.send(PacketLogEntry {
+                                timestamp: Instant::now(),
+                                hash,
+                                direction: PacketDirection::GossipIn,
+                                size: frame.payload.len(),
+                                snr: Some(frame.snr),
+                                rssi: Some(frame.rssi),
+                                action: PacketAction::DroppedRateLimit,
+                            }).await;
+                            continue;
+                        }
+
+                        // Enqueue for radio TX.
+                        if tx_queue.len() >= tx_queue_size {
+                            stats.dropped_queue.fetch_add(1, Ordering::Relaxed);
+                            warn!("TX queue full, dropping packet ({} bytes)", frame.payload.len());
+                            let _ = log_tx.send(PacketLogEntry {
+                                timestamp: Instant::now(),
+                                hash,
+                                direction: PacketDirection::GossipIn,
+                                size: frame.payload.len(),
+                                snr: Some(frame.snr),
+                                rssi: Some(frame.rssi),
+                                action: PacketAction::DroppedQueueFull,
+                            }).await;
+                            continue;
+                        }
+
+                        tx_queue.push_back(frame.payload.clone());
+                        let _ = log_tx.send(PacketLogEntry {
+                            timestamp: Instant::now(),
+                            hash,
+                            direction: PacketDirection::GossipIn,
+                            size: frame.payload.len(),
+                            snr: Some(frame.snr),
+                            rssi: Some(frame.rssi),
+                            action: PacketAction::Bridged,
+                        }).await;
+                    }
+                    GossipEvent::NeighborChanged(count) => {
+                        #[allow(clippy::cast_possible_truncation)]
+                        stats.neighbor_count.store(count as u64, Ordering::Relaxed);
                     }
                 }
             }
@@ -217,19 +307,7 @@ pub async fn run(
 
         // Drain TX queue to radio.
         while let Some(payload) = tx_queue.pop_front() {
-            let size = payload.len();
             stats.radio_tx.fetch_add(1, Ordering::Relaxed);
-            let _ = log_tx
-                .send(PacketLogEntry {
-                    timestamp: Instant::now(),
-                    direction: PacketDirection::RadioTx,
-                    size,
-                    snr: None,
-                    rssi: None,
-                    peer_name: None,
-                    action: PacketAction::Transmitted,
-                })
-                .await;
             if radio_tx.send(payload).await.is_err() {
                 break;
             }
@@ -237,134 +315,110 @@ pub async fn run(
     }
 }
 
-#[allow(clippy::too_many_arguments)]
+#[cfg(test)]
-async fn handle_radio_packet(
+#[allow(clippy::unwrap_used, clippy::expect_used)]
-    our_id: &PublicKey,
+mod tests {
-    seq: &mut u64,
+    use super::*;
-    pkt: &RadioPacket,
-    echo_dedup: &mut DedupCache<[u8; 16]>,
-    net_tx: &mpsc::Sender<(Envelope, Option<PublicKey>)>,
-    stats: &Stats,
-    log_tx: &mpsc::Sender<PacketLogEntry>,
-    names: &PeerNames,
-) {
-    stats.radio_rx.fetch_add(1, Ordering::Relaxed);
 
-    // Check echo suppression.
+    #[test]
-    let hash = content_hash(&pkt.payload);
+    fn dedup_cache_new_key_not_duplicate() {
-    if echo_dedup.check_and_insert(hash) {
+        let mut cache = DedupCache::new(Duration::from_secs(10));
-        stats.dropped_dedup.fetch_add(1, Ordering::Relaxed);
+        assert!(!cache.check_and_insert([0u8; 32]));
-        debug!("radio RX echo suppressed ({} bytes)", pkt.payload.len());
-        let _ = log_tx
-            .send(PacketLogEntry {
-                timestamp: Instant::now(),
-                direction: PacketDirection::RadioRx,
-                size: pkt.payload.len(),
-                snr: Some(pkt.snr),
-                rssi: Some(pkt.rssi),
-                peer_name: None,
-                action: PacketAction::DroppedDedup,
-            })
-            .await;
-        return;
     }
 
-    // Wrap and forward to all peers.
+    #[test]
-    *seq += 1;
+    fn dedup_cache_duplicate_detected() {
-    let envelope = Envelope {
+        let mut cache = DedupCache::new(Duration::from_secs(10));
-        origin: *our_id,
+        cache.check_and_insert([1u8; 32]);
-        seq: *seq,
+        assert!(cache.check_and_insert([1u8; 32]));
-        rssi: pkt.rssi,
-        snr: pkt.snr,
-        payload: pkt.payload.clone(),
-    };
-
-    stats.forwarded.fetch_add(1, Ordering::Relaxed);
-    let _ = net_tx.send((envelope, None)).await;
-    let _ = log_tx
-        .send(PacketLogEntry {
-            timestamp: Instant::now(),
-            direction: PacketDirection::RadioRx,
-            size: pkt.payload.len(),
-            snr: Some(pkt.snr),
-            rssi: Some(pkt.rssi),
-            peer_name: names.get(our_id),
-            action: PacketAction::Forwarded,
-        })
-        .await;
     }
 
-#[allow(clippy::too_many_arguments)]
+    #[test]
-async fn handle_net_packet(
+    fn dedup_cache_different_keys_independent() {
-    from: &PublicKey,
+        let mut cache = DedupCache::new(Duration::from_secs(10));
-    envelope: Envelope,
+        cache.check_and_insert([1u8; 32]);
-    iroh_dedup: &mut DedupCache<(PublicKey, u64)>,
+        assert!(!cache.check_and_insert([2u8; 32]));
-    echo_dedup: &mut DedupCache<[u8; 16]>,
-    tx_queue: &mut VecDeque<Vec<u8>>,
-    tx_queue_size: usize,
-    stats: &Stats,
-    log_tx: &mpsc::Sender<PacketLogEntry>,
-    names: &PeerNames,
-) {
-    // Check iroh-level dedup.
-    if iroh_dedup.check_and_insert((envelope.origin, envelope.seq)) {
-        stats.dropped_dedup.fetch_add(1, Ordering::Relaxed);
-        debug!("net dedup ({} bytes from {})", envelope.payload.len(), fmt_key(from));
-        let _ = log_tx
-            .send(PacketLogEntry {
-                timestamp: Instant::now(),
-                direction: PacketDirection::NetRx,
-                size: envelope.payload.len(),
-                snr: Some(envelope.snr),
-                rssi: Some(envelope.rssi),
-                peer_name: names.get(from),
-                action: PacketAction::DroppedDedup,
-            })
-            .await;
-        return;
     }
 
-    // Insert content hash for radio echo suppression.
+    #[test]
-    let hash = content_hash(&envelope.payload);
+    fn dedup_cache_expired_entry_not_duplicate() {
-    echo_dedup.insert(hash);
+        let mut cache = DedupCache::new(Duration::from_millis(1));
-
+        cache.check_and_insert([1u8; 32]);
-    // Enqueue for radio TX.
+        std::thread::sleep(Duration::from_millis(5));
-    if tx_queue.len() >= tx_queue_size {
+        assert!(!cache.check_and_insert([1u8; 32]));
-        stats.dropped_queue.fetch_add(1, Ordering::Relaxed);
-        warn!("TX queue full, dropping packet ({} bytes)", envelope.payload.len());
-        let _ = log_tx
-            .send(PacketLogEntry {
-                timestamp: Instant::now(),
-                direction: PacketDirection::NetRx,
-                size: envelope.payload.len(),
-                snr: Some(envelope.snr),
-                rssi: Some(envelope.rssi),
-                peer_name: names.get(from),
-                action: PacketAction::DroppedQueueFull,
-            })
-            .await;
-        return;
     }
 
-    tx_queue.push_back(envelope.payload);
+    #[test]
-    let _ = log_tx
+    fn dedup_cache_prune_removes_expired() {
-        .send(PacketLogEntry {
+        let mut cache = DedupCache::new(Duration::from_millis(1));
-            timestamp: Instant::now(),
+        cache.check_and_insert([1u8; 32]);
-            direction: PacketDirection::NetRx,
+        cache.check_and_insert([2u8; 32]);
-            size: tx_queue.back().map(Vec::len).unwrap_or(0),
+        std::thread::sleep(Duration::from_millis(5));
-            snr: Some(envelope.snr),
+        cache.prune();
-            rssi: Some(envelope.rssi),
+        assert!(cache.entries.is_empty());
-            peer_name: names.get(from),
-            action: PacketAction::Transmitted,
-        })
-        .await;
     }
 
-fn fmt_key(pk: &PublicKey) -> String {
+    #[test]
-    let s = pk.to_string();
+    fn dedup_cache_prune_keeps_fresh() {
-    if s.len() > 12 {
+        let mut cache = DedupCache::new(Duration::from_secs(10));
-        format!("{}...", &s[..12])
+        cache.check_and_insert([1u8; 32]);
-    } else {
+        cache.prune();
-        s
+        assert_eq!(cache.entries.len(), 1);
+    }
+
+    #[test]
+    fn stats_snapshot_reflects_increments() {
+        let stats = Stats::default();
+        stats.radio_rx.fetch_add(5, Ordering::Relaxed);
+        stats.gossip_tx.fetch_add(3, Ordering::Relaxed);
+        stats.radio_connected.store(1, Ordering::Relaxed);
+        let snap = stats.snapshot();
+        assert_eq!(snap.radio_rx, 5);
+        assert_eq!(snap.gossip_tx, 3);
+        assert!(snap.radio_connected);
+    }
+
+    #[test]
+    fn stats_default_is_zeroed() {
+        let snap = Stats::default().snapshot();
+        assert_eq!(snap.radio_rx, 0);
+        assert_eq!(snap.gossip_rx, 0);
+        assert!(!snap.radio_connected);
+    }
+
+    #[test]
+    fn packet_action_display() {
+        assert_eq!(format!("{}", PacketAction::Bridged), "");
+        assert_eq!(format!("{}", PacketAction::DroppedDedup), "DUP");
+        assert_eq!(format!("{}", PacketAction::DroppedQueueFull), "FULL");
+        assert_eq!(format!("{}", PacketAction::DroppedRateLimit), "RATE");
+    }
+
+    #[test]
+    fn dedup_cache_ttl_boundary_check_and_insert() {
+        // Force an entry's timestamp to be exactly TTL ago. With `< ttl`, the entry
+        // at exactly TTL is NOT a duplicate. With `<= ttl` (the mutant), it would
+        // wrongly be treated as still live.
+        let ttl = Duration::from_secs(10);
+        let mut cache = DedupCache::new(ttl);
+        cache.check_and_insert([9u8; 32]);
+        // Backdate the entry to exactly TTL ago.
+        let exactly_ttl_ago = Instant::now().checked_sub(ttl).unwrap();
+        cache.entries.insert([9u8; 32], exactly_ttl_ago);
+        // duration_since(exactly_ttl_ago) == ttl, so `< ttl` is false → not duplicate.
+        // The mutant `<= ttl` would say true → duplicate. This catches it.
+        assert!(!cache.check_and_insert([9u8; 32]), "entry at exact TTL must be treated as expired");
+    }
+
+    #[test]
+    fn dedup_cache_ttl_boundary_prune() {
+        let ttl = Duration::from_secs(10);
+        let mut cache = DedupCache::new(ttl);
+        cache.check_and_insert([8u8; 32]);
+        // Backdate to exactly TTL ago.
+        let exactly_ttl_ago = Instant::now().checked_sub(ttl).unwrap();
+        cache.entries.insert([8u8; 32], exactly_ttl_ago);
+        cache.prune();
+        assert!(cache.entries.is_empty(), "entry at exact TTL must be pruned");
     }
 }

src/setup.rs

@@ -0,0 +1,194 @@
+//! Interactive console setup wizard for bridge configuration.
+
+use std::io::{self, Write};
+use std::path::Path;
+
+use anyhow::{Context, Result};
+
+use crate::config::{BridgeSection, Config, RadioSection};
+
+/// ANSI escape helpers.
+const BOLD: &str = "\x1b[1m";
+const DIM: &str = "\x1b[2m";
+const CYAN: &str = "\x1b[36m";
+const GREEN: &str = "\x1b[32m";
+const YELLOW: &str = "\x1b[33m";
+const RESET: &str = "\x1b[0m";
+
+/// Run the interactive setup wizard. If `existing` is Some, use those values as defaults.
+pub fn run_wizard(config_path: &Path, existing: Option<&Config>) -> Result<()> {
+    let defaults = existing
+        .map_or_else(|| (RadioSection::default(), BridgeSection::default()), |c| (c.radio.clone(), c.bridge.clone()));
+    let (radio, bridge) = defaults;
+
+    println!();
+    println!("  {BOLD}donglora-bridge setup{RESET}");
+    println!("  {DIM}Configure your LoRa gossip bridge.{RESET}");
+    println!();
+
+    // ── Passphrase ───────────────────────────────────────────────
+
+    let default_pass = if bridge.passphrase.is_empty() || bridge.passphrase == "change-me" {
+        None
+    } else {
+        Some(bridge.passphrase.as_str())
+    };
+    let passphrase = prompt_required("Passphrase", default_pass)?;
+
+    println!();
+    println!("  {BOLD}Radio Settings{RESET} {DIM}(Enter to keep default){RESET}");
+    println!("  {DIM}────────────────────────────────────{RESET}");
+
+    // ── Radio ────────────────────────────────────────────────────
+
+    let freq_default = format!("{:.3}", f64::from(radio.frequency) / 1_000_000.0);
+    let freq_mhz: f64 = prompt_parse("Frequency (MHz)", &freq_default)?;
+    #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)] // validated by prompt_parse
+    let frequency = (freq_mhz * 1_000_000.0) as u32;
+
+    let bandwidth = prompt_default("Bandwidth", &radio.bandwidth)?;
+
+    let sf_default = format!("{}", radio.spreading_factor);
+    let spreading_factor: u8 = prompt_parse("Spreading Factor", &sf_default)?;
+
+    let cr_default = format!("{}", radio.coding_rate);
+    let coding_rate: u8 = prompt_parse("Coding Rate", &cr_default)?;
+
+    let sw_default = format!("0x{:04X}", radio.sync_word);
+    let sync_word_str = prompt_default("Sync Word", &sw_default)?;
+    let sync_word = parse_sync_word(&sync_word_str)?;
+
+    let tx_power = prompt_default("TX Power (dBm or 'max')", &radio.tx_power)?;
+
+    let pre_default = format!("{}", radio.preamble);
+    let preamble: u16 = prompt_parse("Preamble", &pre_default)?;
+
+    let cad_default = if radio.cad { "on" } else { "off" };
+    let cad_str = prompt_default("CAD", cad_default)?;
+    let cad = matches!(cad_str.to_lowercase().as_str(), "on" | "true" | "yes" | "1");
+
+    let port_default = radio.port.as_deref().unwrap_or("auto");
+    let port_str = prompt_default("Serial Port", port_default)?;
+    let port = if port_str == "auto" || port_str.is_empty() { None } else { Some(port_str) };
+
+    // ── Build and save ───────────────────────────────────────────
+
+    let cfg = Config {
+        radio: RadioSection {
+            port,
+            frequency,
+            bandwidth,
+            spreading_factor,
+            coding_rate,
+            sync_word,
+            tx_power,
+            preamble,
+            cad,
+        },
+        bridge: BridgeSection {
+            passphrase,
+            dedup_window_secs: bridge.dedup_window_secs,
+            tx_queue_size: bridge.tx_queue_size,
+            rate_limit_pps: bridge.rate_limit_pps,
+            log_file: bridge.log_file,
+        },
+    };
+
+    write_config(config_path, &cfg)?;
+
+    println!();
+    println!("  {GREEN}Config saved to {}{RESET}", config_path.display());
+    println!("  Run {CYAN}donglora-bridge{RESET} to start!");
+    println!();
+
+    Ok(())
+}
+
+fn write_config(path: &Path, cfg: &Config) -> Result<()> {
+    if let Some(parent) = path.parent() {
+        std::fs::create_dir_all(parent).with_context(|| format!("creating directory: {}", parent.display()))?;
+    }
+    let content = toml::to_string_pretty(cfg).context("serializing config")?;
+    std::fs::write(path, content).with_context(|| format!("writing config: {}", path.display()))?;
+    Ok(())
+}
+
+// ── Prompt helpers ───────────────────────────────────────────────
+
+fn prompt_default(label: &str, default: &str) -> Result<String> {
+    print!("  {label} {DIM}[{default}]{RESET}: ");
+    io::stdout().flush()?;
+    let mut input = String::new();
+    io::stdin().read_line(&mut input)?;
+    let trimmed = input.trim();
+    if trimmed.is_empty() { Ok(default.to_string()) } else { Ok(trimmed.to_string()) }
+}
+
+fn prompt_required(label: &str, default: Option<&str>) -> Result<String> {
+    loop {
+        let prompt = default.map_or_else(|| format!("  {label}: "), |d| format!("  {label} {DIM}[{d}]{RESET}: "));
+        print!("{prompt}");
+        io::stdout().flush()?;
+        let mut input = String::new();
+        io::stdin().read_line(&mut input)?;
+        let trimmed = input.trim();
+        if !trimmed.is_empty() {
+            return Ok(trimmed.to_string());
+        }
+        if let Some(d) = default {
+            return Ok(d.to_string());
+        }
+        println!("  {YELLOW}This field is required.{RESET}");
+    }
+}
+
+fn prompt_parse<T: std::str::FromStr>(label: &str, default: &str) -> Result<T>
+where
+    T::Err: std::fmt::Display,
+{
+    loop {
+        let input = prompt_default(label, default)?;
+        match input.parse::<T>() {
+            Ok(v) => return Ok(v),
+            Err(e) => println!("  {YELLOW}Invalid input: {e}{RESET}"),
+        }
+    }
+}
+
+fn parse_sync_word(s: &str) -> Result<u16> {
+    let s = s.trim().to_lowercase();
+    let s = s.strip_prefix("0x").unwrap_or(&s);
+    u16::from_str_radix(s, 16).with_context(|| format!("invalid sync word: {s}"))
+}
+
+#[cfg(test)]
+#[allow(clippy::unwrap_used, clippy::expect_used)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parse_sync_word_hex_prefix() {
+        assert_eq!(parse_sync_word("0x3444").unwrap(), 0x3444);
+    }
+
+    #[test]
+    fn parse_sync_word_no_prefix() {
+        assert_eq!(parse_sync_word("3444").unwrap(), 0x3444);
+    }
+
+    #[test]
+    fn parse_sync_word_case_insensitive() {
+        assert_eq!(parse_sync_word("0xABCD").unwrap(), 0xABCD);
+    }
+
+    #[test]
+    fn parse_sync_word_whitespace() {
+        assert_eq!(parse_sync_word("  0x3444  ").unwrap(), 0x3444);
+    }
+
+    #[test]
+    fn parse_sync_word_invalid() {
+        assert!(parse_sync_word("ZZZZ").is_err());
+        assert!(parse_sync_word("").is_err());
+    }
+}