diff --git a/docs/groupmind-local.md b/docs/groupmind-local.md
new file mode 100644
index 0000000..5617a59
--- /dev/null
+++ b/docs/groupmind-local.md
@@ -0,0 +1,52 @@
+# GroupMind Local — offline coordination relay
+
+The fleet normally coordinates through cloud GroupMind. When the internet is
+down but the machines are still on the same LAN (everyone home, ISP outage),
+there is no hub and the agents go silent. **GroupMind Local** is a small
+always-on service — meant to run on the machine that never sleeps (e.g. a Mac
+mini) — that speaks the subset of the GroupMind message API the fleet uses, so
+any agent can fail over to it and keep talking with **zero internet**.
+
+Local models on each machine (an on-device LLM per box) + GroupMind Local as the
+hub = a fleet that reasons and coordinates fully offline.
+
+## Run it
+
+```bash
+# defaults: :18790, store ~/.iak/local-relay.jsonl, LAN-open
+npm run relay
+
+# or explicitly
+node scripts/local-relay.mjs --port 18790 --store ~/.iak/local-relay.jsonl --token "$TOKEN"
+```
+
+Config via env: `IAK_RELAY_PORT`, `IAK_RELAY_STORE`, `IAK_RELAY_TOKEN`.
+If `IAK_RELAY_TOKEN` is set, every request must present it via `X-API-Key` or
+`Authorization: Bearer`. Unset means LAN-open — fine on a trusted home LAN only.
+
+## API (GroupMind-compatible subset)
+
+| Method | Path | Body / Query | Notes |
+| --- | --- | --- | --- |
+| `GET` | `/health` | — | always open; reports message count |
+| `POST` | `/api/v1/messages` | `{ room, body, from?, metadata? }` | create a message |
+| `POST` | `/api/v1/rooms/:room/messages` | `{ body, from?, metadata? }` | create (room in path) |
+| `GET` | `/api/v1/rooms/:room/messages` | `?limit=&since=` | newest-first, GroupMind shape |
+
+An agent points its room client at `http://<mini-lan-ip>:18790/api/v1` when cloud
+GroupMind is unreachable — same paths, just a different base URL.
+
+## Scope (MVP) and what's next
+
+This is a **LAN message store + serve** — deliberately not all of GroupMind
+(no auth DB, no realtime, no reactions). Every stored message carries a UUID and
+`origin: "local-relay"`.
+
+Not yet built (the deliberate next PRs):
+
+1. **Client failover** — the IAK room client trying cloud first, then the local
+   relay, automatically.
+2. **Sync-on-reconnect** — merging the relay's offline history back into cloud
+   GroupMind when the internet returns, deduped by message id. This is the hard
+   part; the UUID + `origin` on every message exist so it can merge without
+   reordering or duplicates.
diff --git a/package.json b/package.json
index c912f11..2520146 100644
--- a/package.json
+++ b/package.json
@@ -10,7 +10,8 @@
   "scripts": {
     "test": "node --test test/*.test.mjs packages/user-intent-kit/test/*.test.js",
     "start": "node bin/cli.mjs serve",
-    "mcp": "node bin/iak-mcp.mjs"
+    "mcp": "node bin/iak-mcp.mjs",
+    "relay": "node scripts/local-relay.mjs"
   },
   "keywords": [
     "ide",
diff --git a/scripts/local-relay.mjs b/scripts/local-relay.mjs
new file mode 100644
index 0000000..ef73265
--- /dev/null
+++ b/scripts/local-relay.mjs
@@ -0,0 +1,192 @@
+#!/usr/bin/env node
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+// iak-local-relay — IAK's offline coordination hub.
+//
+// The fleet normally coordinates through cloud GroupMind (Vercel). When the
+// internet is down but the machines are still on the same LAN (e.g. everyone
+// home, ISP outage), there is no hub and the agents go silent. This is a small
+// always-on service — meant to run on the Mac mini, the machine that never
+// sleeps — that speaks the SUBSET of GroupMind's message API the fleet uses, so
+// an agent can fail over to `http://<mini-lan-ip>:<port>/api/v1` and keep
+// talking with zero internet.
+//
+// Scope (MVP): a LAN message store + serve. It is NOT the whole of GroupMind
+// (no auth DB, no realtime, no reactions) and it does NOT yet reconcile its
+// offline history back into cloud GroupMind when the internet returns — that
+// sync-on-reconnect step (merge by message id) is the deliberate next PR. Every
+// message it stores carries a UUID + `origin: "local-relay"` so that future
+// sync can dedup and merge without reordering.
+//
+// Zero runtime deps (built-in http/fs/crypto only), matching the rest of IAK.
+//
+// Routes:
+//   GET  /health
+//   POST /api/v1/messages                      { room, body, from?, metadata? }
+//   POST /api/v1/rooms/:room/messages          { body, from?, metadata? }
+//   GET  /api/v1/rooms/:room/messages?limit=&since=
+//
+// Auth: if IAK_RELAY_TOKEN is set, every request must present it via X-API-Key
+// or `Authorization: Bearer`. If unset, the relay is LAN-open (it logs one
+// warning) — acceptable on a trusted home LAN, not on an untrusted network.
+//
+// Config (env or startRelay() args): IAK_RELAY_PORT (default 18790),
+// IAK_RELAY_STORE (default ~/.iak/local-relay.jsonl), IAK_RELAY_TOKEN.
+
+import http from 'node:http';
+import { appendFileSync, mkdirSync, readFileSync, existsSync } from 'node:fs';
+import { randomUUID } from 'node:crypto';
+import { homedir } from 'node:os';
+import { dirname, join } from 'node:path';
+
+const DEFAULT_PORT = 18790;
+const DEFAULT_STORE = join(homedir(), '.iak', 'local-relay.jsonl');
+const MAX_LIMIT = 200;
+const DEFAULT_LIMIT = 50;
+const MAX_BODY_BYTES = 256 * 1024; // reject absurd payloads
+
+function readMessages(storePath) {
+  if (!existsSync(storePath)) return [];
+  const out = [];
+  for (const line of readFileSync(storePath, 'utf8').split('\n')) {
+    if (!line.trim()) continue;
+    try { out.push(JSON.parse(line)); } catch { /* skip a corrupt line, never crash a read */ }
+  }
+  return out;
+}
+
+function appendMessage(storePath, msg) {
+  mkdirSync(dirname(storePath), { recursive: true });
+  appendFileSync(storePath, JSON.stringify(msg) + '\n');
+}
+
+function send(res, status, obj) {
+  const payload = JSON.stringify(obj);
+  res.writeHead(status, { 'Content-Type': 'application/json', 'Content-Length': Buffer.byteLength(payload) });
+  res.end(payload);
+}
+
+function readJsonBody(req) {
+  return new Promise((resolve, reject) => {
+    let size = 0;
+    const chunks = [];
+    req.on('data', (c) => {
+      size += c.length;
+      if (size > MAX_BODY_BYTES) { reject(new Error('payload too large')); req.destroy(); return; }
+      chunks.push(c);
+    });
+    req.on('end', () => {
+      const raw = Buffer.concat(chunks).toString('utf8');
+      if (!raw.trim()) return resolve({});
+      try { resolve(JSON.parse(raw)); } catch { reject(new Error('invalid JSON')); }
+    });
+    req.on('error', reject);
+  });
+}
+
+// Build a stored message from an incoming create request. Returns { msg } or
+// { error } for a validation failure.
+function buildMessage({ room, body, from, metadata }) {
+  if (!room || typeof room !== 'string') return { error: 'room is required' };
+  if (!body || typeof body !== 'string') return { error: 'body is required' };
+  return {
+    msg: {
+      id: randomUUID(),
+      room,
+      from: typeof from === 'string' && from ? from : 'unknown',
+      body,
+      metadata: metadata ?? null,
+      created_at: new Date().toISOString(),
+      origin: 'local-relay',
+    },
+  };
+}
+
+/**
+ * Start the relay. Returns the http.Server (already listening).
+ * @param {{port?:number, storePath?:string, token?:string, logger?:(m:string)=>void}} opts
+ */
+export function startRelay(opts = {}) {
+  const envPort = Number(process.env.IAK_RELAY_PORT);
+  const port = opts.port ?? (Number.isFinite(envPort) ? envPort : DEFAULT_PORT);
+  const storePath = opts.storePath ?? process.env.IAK_RELAY_STORE ?? DEFAULT_STORE;
+  const token = opts.token ?? process.env.IAK_RELAY_TOKEN ?? '';
+  const log = opts.logger ?? ((m) => process.stderr.write(`[iak-local-relay] ${m}\n`));
+
+  if (!token) log('WARNING: no IAK_RELAY_TOKEN set — relay is LAN-open (fine on a trusted home LAN only).');
+
+  function authorized(req) {
+    if (!token) return true;
+    const bearer = (req.headers['authorization'] || '').replace(/^Bearer\s+/i, '');
+    return req.headers['x-api-key'] === token || bearer === token;
+  }
+
+  const server = http.createServer(async (req, res) => {
+    try {
+      const url = new URL(req.url, `http://localhost:${port}`);
+      const path = url.pathname.replace(/\/+$/, '') || '/';
+
+      if (req.method === 'GET' && path === '/health') {
+        return send(res, 200, { ok: true, service: 'iak-local-relay', messages: readMessages(storePath).length });
+      }
+
+      if (!authorized(req)) return send(res, 401, { error: 'unauthorized' });
+
+      // GET /api/v1/rooms/:room/messages
+      const getMatch = path.match(/^\/api\/v1\/rooms\/([^/]+)\/messages$/);
+      if (req.method === 'GET' && getMatch) {
+        const room = decodeURIComponent(getMatch[1]);
+        const limit = Math.min(Math.max(1, Number(url.searchParams.get('limit')) || DEFAULT_LIMIT), MAX_LIMIT);
+        const since = url.searchParams.get('since');
+        let msgs = readMessages(storePath).filter((m) => m.room === room);
+        if (since) msgs = msgs.filter((m) => m.created_at > since);
+        // JSONL append order IS chronological, so it orders even messages that
+        // share a millisecond timestamp. Take the last `limit` (newest) and
+        // reverse to newest-first, matching GroupMind's shape.
+        const messages = msgs.slice(-limit).reverse();
+        return send(res, 200, { messages, count: messages.length });
+      }
+
+      // POST /api/v1/messages  { room, body, ... }
+      if (req.method === 'POST' && path === '/api/v1/messages') {
+        const b = await readJsonBody(req);
+        const { msg, error } = buildMessage({ room: b.room, body: b.body, from: b.from, metadata: b.metadata });
+        if (error) return send(res, 400, { error });
+        appendMessage(storePath, msg);
+        return send(res, 201, msg);
+      }
+
+      // POST /api/v1/rooms/:room/messages  { body, ... }
+      const postMatch = path.match(/^\/api\/v1\/rooms\/([^/]+)\/messages$/);
+      if (req.method === 'POST' && postMatch) {
+        const room = decodeURIComponent(postMatch[1]);
+        const b = await readJsonBody(req);
+        const { msg, error } = buildMessage({ room, body: b.body, from: b.from, metadata: b.metadata });
+        if (error) return send(res, 400, { error });
+        appendMessage(storePath, msg);
+        return send(res, 201, msg);
+      }
+
+      return send(res, 404, { error: 'not found' });
+    } catch (err) {
+      const status = /payload too large/.test(err?.message) ? 413 : /invalid JSON/.test(err?.message) ? 400 : 500;
+      return send(res, status, { error: err?.message || 'internal error' });
+    }
+  });
+
+  server.listen(port, () => log(`listening on :${port}  store=${storePath}`));
+  return server;
+}
+
+// CLI entry
+if (import.meta.url === `file://${process.argv[1]}`) {
+  const arg = (name) => {
+    const i = process.argv.indexOf(name);
+    return i !== -1 ? process.argv[i + 1] : undefined;
+  };
+  startRelay({
+    port: Number(arg('--port')) || undefined,
+    storePath: arg('--store'),
+    token: arg('--token'),
+  });
+}
diff --git a/test/local-relay.test.mjs b/test/local-relay.test.mjs
new file mode 100644
index 0000000..9dc29ea
--- /dev/null
+++ b/test/local-relay.test.mjs
@@ -0,0 +1,128 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { once } from 'node:events';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { rmSync } from 'node:fs';
+import { randomUUID } from 'node:crypto';
+import { startRelay } from '../scripts/local-relay.mjs';
+
+// Start a relay on an ephemeral port with an isolated store, run fn, tear down.
+async function withRelay(opts, fn) {
+  const storePath = join(tmpdir(), `iak-relay-test-${randomUUID()}.jsonl`);
+  const server = startRelay({ port: 0, storePath, logger: () => {}, ...opts });
+  await once(server, 'listening');
+  const port = server.address().port;
+  const base = `http://127.0.0.1:${port}`;
+  try {
+    return await fn({ base, storePath, headers: opts.token ? { 'X-API-Key': opts.token } : {} });
+  } finally {
+    server.close();
+    await once(server, 'close');
+    try { rmSync(storePath, { force: true }); } catch { /* ignore */ }
+  }
+}
+
+const j = (h = {}) => ({ 'Content-Type': 'application/json', ...h });
+
+test('health reports ok and message count', async () => {
+  await withRelay({}, async ({ base }) => {
+    const r = await fetch(`${base}/health`);
+    assert.equal(r.status, 200);
+    const d = await r.json();
+    assert.equal(d.ok, true);
+    assert.equal(d.service, 'iak-local-relay');
+    assert.equal(d.messages, 0);
+  });
+});
+
+test('POST /api/v1/messages stores and GET returns it (round trip)', async () => {
+  await withRelay({}, async ({ base, headers }) => {
+    const post = await fetch(`${base}/api/v1/messages`, {
+      method: 'POST', headers: j(headers),
+      body: JSON.stringify({ room: 'r1', body: 'hello', from: '@mm' }),
+    });
+    assert.equal(post.status, 201);
+    const msg = await post.json();
+    assert.ok(msg.id, 'has id');
+    assert.equal(msg.room, 'r1');
+    assert.equal(msg.from, '@mm');
+    assert.equal(msg.body, 'hello');
+    assert.equal(msg.origin, 'local-relay');
+    assert.ok(msg.created_at, 'has created_at');
+
+    const get = await fetch(`${base}/api/v1/rooms/r1/messages`, { headers });
+    assert.equal(get.status, 200);
+    const { messages, count } = await get.json();
+    assert.equal(count, 1);
+    assert.equal(messages[0].body, 'hello');
+    assert.equal(messages[0].id, msg.id);
+  });
+});
+
+test('POST /api/v1/rooms/:room/messages (path form) works and room filters', async () => {
+  await withRelay({}, async ({ base, headers }) => {
+    await fetch(`${base}/api/v1/rooms/alpha/messages`, {
+      method: 'POST', headers: j(headers), body: JSON.stringify({ body: 'in-alpha' }),
+    });
+    await fetch(`${base}/api/v1/messages`, {
+      method: 'POST', headers: j(headers), body: JSON.stringify({ room: 'beta', body: 'in-beta' }),
+    });
+    const alpha = await (await fetch(`${base}/api/v1/rooms/alpha/messages`, { headers })).json();
+    assert.equal(alpha.count, 1);
+    assert.equal(alpha.messages[0].body, 'in-alpha');
+    const beta = await (await fetch(`${base}/api/v1/rooms/beta/messages`, { headers })).json();
+    assert.equal(beta.count, 1);
+    assert.equal(beta.messages[0].body, 'in-beta');
+  });
+});
+
+test('GET honors limit and returns newest-first', async () => {
+  await withRelay({}, async ({ base, headers }) => {
+    for (const n of [1, 2, 3]) {
+      await fetch(`${base}/api/v1/messages`, {
+        method: 'POST', headers: j(headers), body: JSON.stringify({ room: 'r', body: `m${n}` }),
+      });
+    }
+    const { messages, count } = await (await fetch(`${base}/api/v1/rooms/r/messages?limit=2`, { headers })).json();
+    assert.equal(count, 2);
+    assert.equal(messages[0].body, 'm3', 'newest first');
+  });
+});
+
+test('POST without body is rejected 400', async () => {
+  await withRelay({}, async ({ base, headers }) => {
+    const r = await fetch(`${base}/api/v1/messages`, {
+      method: 'POST', headers: j(headers), body: JSON.stringify({ room: 'r' }),
+    });
+    assert.equal(r.status, 400);
+  });
+});
+
+test('malformed JSON body is rejected 400 (never crashes)', async () => {
+  await withRelay({}, async ({ base, headers }) => {
+    const r = await fetch(`${base}/api/v1/messages`, { method: 'POST', headers: j(headers), body: 'not json' });
+    assert.equal(r.status, 400);
+  });
+});
+
+test('token auth: rejects missing/wrong key, accepts correct', async () => {
+  await withRelay({ token: 'secret123' }, async ({ base }) => {
+    const noKey = await fetch(`${base}/api/v1/rooms/r/messages`);
+    assert.equal(noKey.status, 401);
+    const wrong = await fetch(`${base}/api/v1/rooms/r/messages`, { headers: { 'X-API-Key': 'nope' } });
+    assert.equal(wrong.status, 401);
+    const right = await fetch(`${base}/api/v1/rooms/r/messages`, { headers: { 'X-API-Key': 'secret123' } });
+    assert.equal(right.status, 200);
+    // health stays open even with a token configured
+    const health = await fetch(`${base}/health`);
+    assert.equal(health.status, 200);
+  });
+});
+
+test('unknown route is 404', async () => {
+  await withRelay({}, async ({ base, headers }) => {
+    const r = await fetch(`${base}/api/v1/nope`, { headers });
+    assert.equal(r.status, 404);
+  });
+});