diff --git a/README.md b/README.md
index 0c951c6..fe76712 100644
--- a/README.md
+++ b/README.md
@@ -13,13 +13,19 @@ the `archy` (Archipelago) codebase. This repo is intentionally standalone.
 
 ## Status
 
-Pre-design. See `docs/ARCHITECTURE.md` (in progress) for the protocol
-research and bridge design space.
+Architecture phase done — see `docs/ARCHITECTURE.md` for the protocol
+research, hardware constraints (target: Heltec WiFi LoRa 32 V3), and
+phased plan. **Phase 0** (host-side bridge across 3 separate stock-firmware
+boards) is written — see `host-bridge/` — but not yet hardware-tested; no
+LoRa boards have been attached to the dev machine this was written on.
 
 ## Layout
 
 - `docs/` — protocol research notes and architecture/design docs
-- `firmware/` — device firmware (once design lands)
+- `host-bridge/` — Phase 0: Python bridge relaying text between real
+  Meshtastic/MeshCore/RNode-Reticulum boards over each project's official
+  client protocol
+- `firmware/` — Phase 1+ embedded firmware (once Phase 0 is validated on hardware)
 - `hardware/` — reference hardware notes / board selection
 
 ## Non-goals (for now)
diff --git a/host-bridge/README.md b/host-bridge/README.md
new file mode 100644
index 0000000..b617be5
--- /dev/null
+++ b/host-bridge/README.md
@@ -0,0 +1,77 @@
+# host-bridge (Phase 0)
+
+A host-side Python bridge that connects to one radio per network —
+Meshtastic, MeshCore, and Reticulum (via an RNode-flashed board) — over
+each project's **official** client protocol, and relays text messages
+between all three. See `../docs/ARCHITECTURE.md` for why this is Phase 0
+(prove the cross-network translation logic on 3 separate boards, no
+custom firmware) rather than Phase 1 (one time-multiplexed radio on a
+single Heltec V3).
+
+## Status
+
+**Written, not yet hardware-tested.** Every library call has been checked
+against the upstream project's actual source/docs (see comments in each
+`adapters/*.py` file for what was verified and how), and all four
+dependencies (`meshtastic`, `meshcore`, `rns`, `lxmf`) install and import
+cleanly. What's unverified is the actual on-air behavior once real radios
+are attached — that requires the three boards described below.
+
+## What you need to test this for real
+
+- A Meshtastic-flashed board (e.g. Heltec V3) connected via USB serial or reachable over TCP (ESP32 WiFi build)
+- A MeshCore companion-radio-flashed board, serial or TCP
+- An RNode-flashed board (any RNode-compatible LoRa board) reachable via RNS's serial interface — configure this the same way archy's own `core/archipelago/src/mesh/reticulum.rs` KISS interface does, since this bridge uses the standard `rns`/`lxmf` Python packages, not a custom implementation
+- All three radios need actual antennas/RF range to each other's respective real-world networks to see any traffic worth relaying — this is not simulatable without a radio in the loop
+
+## Install
+
+```bash
+python3 -m venv venv
+source venv/bin/activate
+pip install -r requirements.txt
+```
+
+## Run
+
+```bash
+python3 main.py \
+    --meshtastic-port /dev/ttyUSB0 \
+    --meshcore-port /dev/ttyUSB1 \
+    --reticulum-storage ./rns-storage
+```
+
+Use `--meshtastic-host`/`--meshcore-host` instead of the `-port` flags if a
+board is reachable over TCP (e.g. an ESP32 WiFi build) instead of USB
+serial. Run `python3 main.py --help` for the full flag list.
+
+## How relaying works
+
+Each adapter pushes received text onto a shared, thread-safe queue
+(`bridge_core.MessageBus`). A single dispatcher loop in `main.py` pulls
+each message off, tags it with its origin network + sender, and re-sends
+it on the other two networks — never back onto the network it came from.
+
+Content-hash dedup (`MessageBus.is_duplicate`, 5-minute TTL by default)
+stops the obvious relay loop (the bridge re-hearing its own relayed
+copy). This is a known-simple v0 approach — it can't distinguish two
+different messages that happen to have identical text within the TTL
+window, and it doesn't help if there are *multiple* archy-messh bridges
+active near each other. Good enough to prove the concept; revisit once
+Phase 1 needs something more robust.
+
+## Known gaps (by design, for v0)
+
+- **Reticulum has no broadcast-channel primitive.** Meshtastic has channel
+  PSKs, MeshCore has public channel indices — Reticulum/LXMF messaging is
+  point-to-point between Destinations. `ReticulumAdapter` fakes broadcast
+  by tracking a roster of peer delivery-destinations learned from their
+  LXMF announces and fanning out to all of them individually. A shared
+  symmetric-key Reticulum `GROUP` destination would be a closer analog to
+  a real channel — noted as a follow-up, not implemented here.
+- **MeshCore channel messages carry no sender identity at the protocol
+  level** (verified against `meshcore/reader.py` — `CHANNEL_MSG_RECV` has
+  no pubkey/name field). MeshCore apps convey sender identity by
+  convention inside the message text itself; this bridge doesn't attempt
+  to parse that out, so messages relayed *from* MeshCore show `?` as the
+  sender.
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diff --git a/host-bridge/adapters/__init__.py b/host-bridge/adapters/__init__.py
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diff --git a/host-bridge/adapters/__pycache__/reticulum_adapter.cpython-313.pyc b/host-bridge/adapters/__pycache__/reticulum_adapter.cpython-313.pyc
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diff --git a/host-bridge/adapters/meshcore_adapter.py b/host-bridge/adapters/meshcore_adapter.py
new file mode 100644
index 0000000..cc98ebd
--- /dev/null
+++ b/host-bridge/adapters/meshcore_adapter.py
@@ -0,0 +1,83 @@
+"""MeshCore adapter — wraps the official `meshcore` (meshcore_py) async client.
+
+meshcore_py is asyncio-native (MeshCore.create_serial/create_tcp/create_ble,
+event subscription via meshcore.subscribe(EventType.X, coroutine_handler)).
+The rest of this bridge is thread/callback-based (Meshtastic's pubsub,
+Reticulum's RNS transport thread), so this adapter owns a dedicated event
+loop on a background thread and exposes plain synchronous connect()/send()/
+close() methods, matching the shape of the other two adapters.
+"""
+
+import asyncio
+import threading
+from collections.abc import Callable
+
+
+class MeshCoreAdapter:
+    NETWORK = "meshcore"
+
+    def __init__(
+        self,
+        on_message: Callable[[str, str, str], None],
+        port: str | None = None,
+        host: str | None = None,
+        tcp_port: int = 4000,
+        channel_idx: int = 0,
+    ):
+        """port: serial device path. host: TCP hostname/IP (mutually exclusive
+        with port). channel_idx: which MeshCore public channel to bridge —
+        channel 0 is the default public channel on stock firmware.
+        """
+        self._on_message = on_message
+        self._port = port
+        self._host = host
+        self._tcp_port = tcp_port
+        self._channel_idx = channel_idx
+        self._mc = None
+        self._loop: asyncio.AbstractEventLoop | None = None
+        self._thread: threading.Thread | None = None
+
+    def connect(self) -> None:
+        ready = threading.Event()
+        self._thread = threading.Thread(target=self._run_loop, args=(ready,), daemon=True)
+        self._thread.start()
+        ready.wait(timeout=15)
+
+    def _run_loop(self, ready: threading.Event) -> None:
+        self._loop = asyncio.new_event_loop()
+        asyncio.set_event_loop(self._loop)
+        self._loop.run_until_complete(self._connect_async())
+        ready.set()
+        self._loop.run_forever()
+
+    async def _connect_async(self) -> None:
+        from meshcore import EventType, MeshCore
+
+        if self._host:
+            self._mc = await MeshCore.create_tcp(self._host, self._tcp_port)
+        else:
+            self._mc = await MeshCore.create_serial(self._port or "/dev/ttyUSB0")
+
+        self._mc.subscribe(EventType.CHANNEL_MSG_RECV, self._handle_channel_msg)
+
+    async def _handle_channel_msg(self, event) -> None:  # noqa: ANN001
+        data = event.payload
+        if data.get("channel_idx") != self._channel_idx:
+            return
+        text = data.get("text", "")
+        if text:
+            # CHANNEL_MSG_RECV carries no sender identity at the protocol
+            # level (verified against meshcore/reader.py) — MeshCore apps
+            # convey the sender by convention inside the text itself.
+            self._on_message(self.NETWORK, "?", text)
+
+    def send(self, text: str) -> None:
+        if self._mc is None or self._loop is None:
+            raise RuntimeError("MeshCoreAdapter.send() called before connect()")
+        asyncio.run_coroutine_threadsafe(
+            self._mc.commands.send_chan_msg(self._channel_idx, text), self._loop
+        )
+
+    def close(self) -> None:
+        if self._loop is not None:
+            self._loop.call_soon_threadsafe(self._loop.stop)
diff --git a/host-bridge/adapters/meshtastic_adapter.py b/host-bridge/adapters/meshtastic_adapter.py
new file mode 100644
index 0000000..4e63436
--- /dev/null
+++ b/host-bridge/adapters/meshtastic_adapter.py
@@ -0,0 +1,57 @@
+"""Meshtastic adapter — wraps the official `meshtastic` Python client.
+
+Uses the same pubsub pattern as meshtastic/python's own examples
+(examples/replymessage.py, examples/tcp_pubsub_send_and_receive.py):
+subscribe to the "meshtastic.receive" topic, filter for text packets,
+send via MeshInterface.sendText().
+"""
+
+from collections.abc import Callable
+
+from pubsub import pub
+
+
+class MeshtasticAdapter:
+    NETWORK = "meshtastic"
+
+    def __init__(
+        self,
+        on_message: Callable[[str, str, str], None],
+        port: str | None = None,
+        host: str | None = None,
+    ):
+        """port: serial device path (e.g. /dev/ttyUSB0). host: TCP hostname/IP.
+        Exactly one of port/host should be set; if neither is set, the
+        underlying library auto-detects a serial device.
+        """
+        self._on_message = on_message
+        self._port = port
+        self._host = host
+        self._iface = None
+
+    def connect(self) -> None:
+        import meshtastic.serial_interface
+        import meshtastic.tcp_interface
+
+        pub.subscribe(self._handle_receive, "meshtastic.receive")
+
+        if self._host:
+            self._iface = meshtastic.tcp_interface.TCPInterface(hostname=self._host, timeout=10)
+        else:
+            self._iface = meshtastic.serial_interface.SerialInterface(devPath=self._port, timeout=10)
+
+    def _handle_receive(self, packet: dict, interface) -> None:  # noqa: ANN001
+        text = packet.get("decoded", {}).get("text")
+        if not text:
+            return
+        sender = packet.get("fromId") or str(packet.get("from"))
+        self._on_message(self.NETWORK, sender, text)
+
+    def send(self, text: str) -> None:
+        if self._iface is None:
+            raise RuntimeError("MeshtasticAdapter.send() called before connect()")
+        self._iface.sendText(text)
+
+    def close(self) -> None:
+        if self._iface is not None:
+            self._iface.close()
diff --git a/host-bridge/adapters/reticulum_adapter.py b/host-bridge/adapters/reticulum_adapter.py
new file mode 100644
index 0000000..b56366f
--- /dev/null
+++ b/host-bridge/adapters/reticulum_adapter.py
@@ -0,0 +1,96 @@
+"""Reticulum adapter — wraps RNS + LXMF (the standard host-side Reticulum
+messaging stack; see docs/ARCHITECTURE.md for why archy-messh talks to a
+real RNode-flashed radio via RNS rather than reimplementing Reticulum's
+wire format from scratch).
+
+Reticulum has no built-in broadcast-channel concept the way Meshtastic
+("channel" PSK) or MeshCore ("public channel index") do — LXMF messaging is
+addressed point-to-point between Destinations. To bridge broadcast-style
+text, this adapter tracks a roster of peer LXMF delivery destinations
+learned from their announces (any Reticulum/Sideband/NomadNet/MeshChat user
+who has announced is added), and fans outbound bridge messages out to that
+roster individually. This is the simplest correct v0; a dedicated shared
+GROUP destination (symmetric-key, closer to a real "channel") is a known
+follow-up once Phase 0 proves the roster approach works at all.
+"""
+
+import threading
+from collections.abc import Callable
+
+
+class ReticulumAdapter:
+    NETWORK = "reticulum"
+    ASPECT = "lxmf.delivery"
+
+    def __init__(
+        self,
+        on_message: Callable[[str, str, str], None],
+        storage_path: str,
+        display_name: str = "archy-messh-bridge",
+    ):
+        self._on_message = on_message
+        self._storage_path = storage_path
+        self._display_name = display_name
+        self._router = None
+        self._identity = None
+        self._destination = None
+        self._peers: set[bytes] = set()
+        self._lock = threading.Lock()
+
+        # RNS.Transport.register_announce_handler() requires an object with
+        # an `aspect_filter` attribute — set here so `self` can be registered
+        # directly as the announce handler.
+        self.aspect_filter = self.ASPECT
+
+    def connect(self) -> None:
+        import RNS
+        import LXMF
+
+        RNS.Reticulum()
+        self._router = LXMF.LXMRouter(storagepath=self._storage_path)
+        self._identity = RNS.Identity()
+        self._destination = self._router.register_delivery_identity(
+            self._identity, display_name=self._display_name
+        )
+        self._router.register_delivery_callback(self._handle_delivery)
+        RNS.Transport.register_announce_handler(self)
+        self._router.announce(self._destination.hash)
+
+    def received_announce(self, destination_hash, announced_identity, app_data) -> None:  # noqa: ANN001
+        if self._destination is not None and destination_hash == self._destination.hash:
+            return  # ignore our own announce
+        with self._lock:
+            self._peers.add(destination_hash)
+
+    def _handle_delivery(self, message) -> None:  # noqa: ANN001
+        import RNS
+
+        text = message.content_as_string()
+        sender = RNS.prettyhexrep(message.source_hash)
+        if text:
+            self._on_message(self.NETWORK, sender, text)
+
+    def send(self, text: str) -> None:
+        import RNS
+        import LXMF
+
+        if self._router is None or self._destination is None:
+            raise RuntimeError("ReticulumAdapter.send() called before connect()")
+
+        with self._lock:
+            peer_hashes = list(self._peers)
+
+        for peer_hash in peer_hashes:
+            identity = RNS.Identity.recall(peer_hash)
+            if identity is None:
+                continue  # no path/identity known yet for this peer
+            dest = RNS.Destination(
+                identity, RNS.Destination.OUT, RNS.Destination.SINGLE, "lxmf", "delivery"
+            )
+            lxm = LXMF.LXMessage(
+                dest, self._destination, text, desired_method=LXMF.LXMessage.OPPORTUNISTIC
+            )
+            self._router.handle_outbound(lxm)
+
+    def close(self) -> None:
+        pass  # RNS/LXMF manage their own threads; no explicit teardown needed for a v0 prototype
diff --git a/host-bridge/bridge_core.py b/host-bridge/bridge_core.py
new file mode 100644
index 0000000..90e21f0
--- /dev/null
+++ b/host-bridge/bridge_core.py
@@ -0,0 +1,60 @@
+"""Shared message bus + loop-prevention core for the archy-messh Phase 0 bridge.
+
+Each protocol adapter runs on its own thread/event loop (Meshtastic's pubsub
+callbacks fire from its internal reader thread, MeshCore is asyncio-native,
+Reticulum/LXMF invoke callbacks from RNS's internal transport thread). All
+three push into this single thread-safe queue so one dispatcher can fan
+messages out across protocols without each adapter needing to know about
+the others.
+"""
+
+import hashlib
+import queue
+import threading
+import time
+from dataclasses import dataclass
+
+
+@dataclass
+class BridgeMessage:
+    network: str        # "meshtastic" | "meshcore" | "reticulum"
+    sender: str
+    text: str
+    received_at: float
+
+
+class MessageBus:
+    """Thread-safe inbox with content-hash dedup to prevent repeat loops.
+
+    Dedup is content-hash based (not per-network packet-id based), since the
+    whole point of the bridge is that the same text shows up natively on all
+    three networks once relayed. A short TTL window is enough to stop the
+    obvious loop (bridge re-hears its own relayed copy) without needing any
+    cross-protocol message-id scheme, which doesn't exist.
+    """
+
+    def __init__(self, dedup_ttl_seconds: float = 300.0):
+        self._queue: "queue.Queue[BridgeMessage]" = queue.Queue()
+        self._dedup_ttl = dedup_ttl_seconds
+        self._seen: dict[str, float] = {}
+        self._lock = threading.Lock()
+
+    @staticmethod
+    def _content_hash(text: str) -> str:
+        return hashlib.sha256(text.strip().encode("utf-8")).hexdigest()
+
+    def publish(self, message: BridgeMessage) -> None:
+        self._queue.put(message)
+
+    def is_duplicate(self, text: str) -> bool:
+        h = self._content_hash(text)
+        now = time.monotonic()
+        with self._lock:
+            self._seen = {k: v for k, v in self._seen.items() if v > now}
+            if h in self._seen:
+                return True
+            self._seen[h] = now + self._dedup_ttl
+            return False
+
+    def get(self, timeout: float | None = None) -> BridgeMessage:
+        return self._queue.get(timeout=timeout)
diff --git a/host-bridge/main.py b/host-bridge/main.py
new file mode 100644
index 0000000..99f51a1
--- /dev/null
+++ b/host-bridge/main.py
@@ -0,0 +1,103 @@
+#!/usr/bin/env python3
+"""archy-messh Phase 0 host-bridge.
+
+Connects to one radio per network (Meshtastic, MeshCore, Reticulum/RNode),
+each over its official client protocol, and relays text messages between
+all three. See docs/ARCHITECTURE.md for why this is Phase 0 (prove the
+bridging logic on 3 separate boards) rather than Phase 1 (single
+time-multiplexed radio on one Heltec V3).
+
+NOT YET TESTED END-TO-END — written without physical hardware attached to
+the dev machine. Needs Meshtastic + MeshCore + RNode-flashed boards to
+validate; each adapter's wire-level behavior is only as good as its
+upstream library's docs/examples (cited in each adapter's docstring/header).
+
+Usage (see README.md for full option list):
+    python3 main.py \\
+        --meshtastic-port /dev/ttyUSB0 \\
+        --meshcore-port /dev/ttyUSB1 \\
+        --reticulum-storage ./rns-storage
+"""
+
+import argparse
+import sys
+import time
+
+from adapters.meshcore_adapter import MeshCoreAdapter
+from adapters.meshtastic_adapter import MeshtasticAdapter
+from adapters.reticulum_adapter import ReticulumAdapter
+from bridge_core import BridgeMessage, MessageBus
+
+
+def build_arg_parser() -> argparse.ArgumentParser:
+    p = argparse.ArgumentParser(description="archy-messh Phase 0 tri-protocol bridge")
+    p.add_argument("--meshtastic-port", help="Meshtastic serial device (e.g. /dev/ttyUSB0)")
+    p.add_argument("--meshtastic-host", help="Meshtastic TCP host, instead of serial")
+    p.add_argument("--meshcore-port", help="MeshCore serial device (e.g. /dev/ttyUSB1)")
+    p.add_argument("--meshcore-host", help="MeshCore TCP host, instead of serial")
+    p.add_argument("--meshcore-channel", type=int, default=0, help="MeshCore public channel index")
+    p.add_argument(
+        "--reticulum-storage", default="./rns-storage", help="LXMF/RNS storage directory"
+    )
+    p.add_argument(
+        "--dedup-ttl", type=float, default=300.0, help="Seconds to suppress repeat-content loops"
+    )
+    return p
+
+
+def main() -> int:
+    args = build_arg_parser().parse_args()
+
+    bus = MessageBus(dedup_ttl_seconds=args.dedup_ttl)
+
+    def on_message(network: str, sender: str, text: str) -> None:
+        bus.publish(BridgeMessage(network=network, sender=sender, text=text, received_at=time.time()))
+
+    meshtastic = MeshtasticAdapter(on_message, port=args.meshtastic_port, host=args.meshtastic_host)
+    meshcore = MeshCoreAdapter(
+        on_message,
+        port=args.meshcore_port,
+        host=args.meshcore_host,
+        channel_idx=args.meshcore_channel,
+    )
+    reticulum = ReticulumAdapter(on_message, storage_path=args.reticulum_storage)
+
+    adapters = {
+        MeshtasticAdapter.NETWORK: meshtastic,
+        MeshCoreAdapter.NETWORK: meshcore,
+        ReticulumAdapter.NETWORK: reticulum,
+    }
+
+    print("Connecting to Meshtastic...")
+    meshtastic.connect()
+    print("Connecting to MeshCore...")
+    meshcore.connect()
+    print("Connecting to Reticulum...")
+    reticulum.connect()
+    print("All three adapters connected. Bridging...")
+
+    try:
+        while True:
+            message = bus.get()
+            if bus.is_duplicate(message.text):
+                continue
+            print(f"[{message.network}] {message.sender}: {message.text}")
+            for network, adapter in adapters.items():
+                if network == message.network:
+                    continue  # don't echo back onto the network it came from
+                try:
+                    adapter.send(f"[{message.network}/{message.sender}] {message.text}")
+                except Exception as exc:  # noqa: BLE001
+                    print(f"  ! failed to relay onto {network}: {exc}", file=sys.stderr)
+    except KeyboardInterrupt:
+        pass
+    finally:
+        meshtastic.close()
+        meshcore.close()
+        reticulum.close()
+
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/host-bridge/requirements.txt b/host-bridge/requirements.txt
new file mode 100644
index 0000000..b14f6b3
--- /dev/null
+++ b/host-bridge/requirements.txt
@@ -0,0 +1,4 @@
+meshtastic>=2.7.10
+meshcore>=2.3.7
+rns>=1.3.5
+lxmf>=1.0.1