diff --git a/apps/appservice/package.json b/apps/appservice/package.json
new file mode 100644
index 0000000..3298699
--- /dev/null
+++ b/apps/appservice/package.json
@@ -0,0 +1,35 @@
+{
+  "name": "@mosaicstack/mosaic-as",
+  "version": "0.0.1",
+  "type": "module",
+  "private": true,
+  "repository": {
+    "type": "git",
+    "url": "https://git.mosaicstack.dev/mosaicstack/stack.git",
+    "directory": "apps/appservice"
+  },
+  "main": "dist/main.js",
+  "bin": {
+    "mosaic-as": "dist/main.js",
+    "mosaic-as-registration": "dist/registration-main.js"
+  },
+  "scripts": {
+    "build": "tsc",
+    "lint": "eslint src",
+    "typecheck": "tsc --noEmit",
+    "test": "vitest run --passWithNoTests",
+    "dev": "tsx watch src/main.ts"
+  },
+  "dependencies": {
+    "@mosaicstack/appservice": "workspace:*"
+  },
+  "devDependencies": {
+    "@types/node": "^22.0.0",
+    "tsx": "^4.19.0",
+    "typescript": "^5.8.0",
+    "vitest": "^2.0.0"
+  },
+  "files": [
+    "dist"
+  ]
+}
diff --git a/apps/appservice/src/__tests__/server.test.ts b/apps/appservice/src/__tests__/server.test.ts
new file mode 100644
index 0000000..6a2658a
--- /dev/null
+++ b/apps/appservice/src/__tests__/server.test.ts
@@ -0,0 +1,152 @@
+import { describe, expect, it, vi } from 'vitest';
+
+import { AppserviceDaemon } from '../server.js';
+import type { DaemonConfig, DaemonRequest } from '../server.js';
+
+const cfg: DaemonConfig = {
+  homeserverUrl: 'https://hs.example',
+  domain: 'hs.example',
+  asToken: 'as-secret',
+  hsToken: 'hs-secret',
+  bridgeTokens: ['bridge-secret'],
+};
+
+const jsonResponse = (status: number, body: unknown): Response =>
+  new Response(JSON.stringify(body), { status, headers: { 'Content-Type': 'application/json' } });
+
+const request = (overrides: Partial<DaemonRequest>): DaemonRequest => ({
+  method: 'GET',
+  path: '/',
+  searchParams: new URLSearchParams(),
+  body: undefined,
+  ...overrides,
+});
+
+const makeDaemon = () => {
+  const fetchMock = vi.fn(async (_input: URL | string) => jsonResponse(200, { event_id: '$sent' }));
+  const daemon = new AppserviceDaemon(cfg, fetchMock as unknown as typeof fetch, () => {});
+  return { daemon, fetchMock };
+};
+
+describe('AppserviceDaemon routing', () => {
+  it('serves health unauthenticated', async () => {
+    const { daemon } = makeDaemon();
+    expect((await daemon.handle(request({ path: '/health' }))).status).toBe(200);
+  });
+
+  it('404s unknown paths', async () => {
+    const { daemon } = makeDaemon();
+    expect((await daemon.handle(request({ path: '/nope' }))).status).toBe(404);
+  });
+
+  it('transactions require the hs_token', async () => {
+    const { daemon } = makeDaemon();
+    const bad = await daemon.handle(
+      request({
+        method: 'PUT',
+        path: '/_matrix/app/v1/transactions/t1',
+        authorizationHeader: 'Bearer wrong',
+        body: { events: [] },
+      }),
+    );
+    expect(bad.status).toBe(403);
+    const ok = await daemon.handle(
+      request({
+        method: 'PUT',
+        path: '/_matrix/app/v1/transactions/t1',
+        authorizationHeader: 'Bearer hs-secret',
+        body: { events: [{ type: 'm.room.message', event_id: '$e' }] },
+      }),
+    );
+    expect(ok.status).toBe(200);
+  });
+
+  it('bridge requires a bridge token (hs/as tokens do not work)', async () => {
+    const { daemon } = makeDaemon();
+    for (const token of [undefined, 'Bearer hs-secret', 'Bearer as-secret', 'Bearer nope']) {
+      const res = await daemon.handle(
+        request({
+          method: 'POST',
+          path: '/bridge/v1/messages',
+          authorizationHeader: token,
+          body: {},
+        }),
+      );
+      expect(res.status).toBe(403);
+    }
+  });
+
+  it('bridge message sends as the agent and returns the event id', async () => {
+    const { daemon, fetchMock } = makeDaemon();
+    const res = await daemon.handle(
+      request({
+        method: 'POST',
+        path: '/bridge/v1/messages',
+        authorizationHeader: 'Bearer bridge-secret',
+        body: { room_id: '!r:hs.example', agent: 'pi0-web1', body: 'hi', thread_root: '$req' },
+      }),
+    );
+    expect(res.status).toBe(200);
+    expect(res.body.event_id).toBe('$sent');
+    const sendCall = fetchMock.mock.calls
+      .map((c) => new URL(String(c[0])))
+      .find((u) => u.pathname.includes('/send/m.room.message/'));
+    expect(sendCall).toBeDefined();
+    expect(sendCall!.searchParams.get('user_id')).toBe('@agent-pi0-web1:hs.example');
+  });
+
+  it('bridge rejects invalid payloads with 400', async () => {
+    const { daemon } = makeDaemon();
+    const res = await daemon.handle(
+      request({
+        method: 'POST',
+        path: '/bridge/v1/messages',
+        authorizationHeader: 'Bearer bridge-secret',
+        body: { room_id: 'bad', agent: 'pi0', body: 'x' },
+      }),
+    );
+    expect(res.status).toBe(400);
+  });
+
+  it('bridge typing endpoint works', async () => {
+    const { daemon, fetchMock } = makeDaemon();
+    const res = await daemon.handle(
+      request({
+        method: 'POST',
+        path: '/bridge/v1/typing',
+        authorizationHeader: 'Bearer bridge-secret',
+        body: { room_id: '!r:hs.example', agent: 'pi0-web1', typing: true },
+      }),
+    );
+    expect(res.status).toBe(200);
+    const typingCall = fetchMock.mock.calls
+      .map((c) => new URL(String(c[0])))
+      .find((u) => u.pathname.includes('/typing/'));
+    expect(typingCall).toBeDefined();
+  });
+
+  it('authenticated unknown bridge sub-paths return 405, never fall through', async () => {
+    const { daemon } = makeDaemon();
+    const res = await daemon.handle(
+      request({
+        method: 'GET',
+        path: '/bridge/v1/unknown',
+        authorizationHeader: 'Bearer bridge-secret',
+      }),
+    );
+    expect(res.status).toBe(405);
+  });
+
+  it('empty bridge token list denies everything', async () => {
+    const daemon = new AppserviceDaemon({ ...cfg, bridgeTokens: [] }, undefined, () => {});
+    const res = await daemon.handle(
+      request({
+        method: 'POST',
+        path: '/bridge/v1/typing',
+        authorizationHeader: 'Bearer bridge-secret',
+        body: {},
+      }),
+    );
+    expect(res.status).toBe(403);
+  });
+});
diff --git a/apps/appservice/src/config.ts b/apps/appservice/src/config.ts
new file mode 100644
index 0000000..ae65894
--- /dev/null
+++ b/apps/appservice/src/config.ts
@@ -0,0 +1,23 @@
+import type { DaemonConfig } from './server.js';
+
+const required = (name: string): string => {
+  const value = process.env[name];
+  if (!value) throw new Error(`missing required env var ${name}`);
+  return value;
+};
+
+export function configFromEnv(): DaemonConfig & { port: number } {
+  return {
+    homeserverUrl: required('MOSAIC_AS_HOMESERVER_URL'),
+    domain: required('MOSAIC_AS_DOMAIN'),
+    asToken: required('MOSAIC_AS_TOKEN'),
+    hsToken: required('MOSAIC_HS_TOKEN'),
+    userPrefix: process.env.MOSAIC_AS_USER_PREFIX ?? 'agent-',
+    senderLocalpart: process.env.MOSAIC_AS_SENDER_LOCALPART ?? 'mosaic-as',
+    bridgeTokens: (process.env.MOSAIC_AS_BRIDGE_TOKENS ?? '')
+      .split(',')
+      .map((t) => t.trim())
+      .filter(Boolean),
+    port: Number(process.env.MOSAIC_AS_PORT ?? 8008),
+  };
+}
diff --git a/apps/appservice/src/main.ts b/apps/appservice/src/main.ts
new file mode 100644
index 0000000..5258d88
--- /dev/null
+++ b/apps/appservice/src/main.ts
@@ -0,0 +1,67 @@
+import http from 'node:http';
+
+import { configFromEnv } from './config.js';
+import { AppserviceDaemon } from './server.js';
+
+const cfg = configFromEnv();
+const daemon = new AppserviceDaemon(cfg);
+
+const MAX_BODY_BYTES = 1024 * 1024;
+
+const server = http.createServer((req, res) => {
+  const chunks: Buffer[] = [];
+  let received = 0;
+  let rejected = false;
+  req.on('data', (chunk: Buffer) => {
+    received += chunk.length;
+    if (received > MAX_BODY_BYTES) {
+      rejected = true;
+      res.writeHead(413, { 'Content-Type': 'application/json' });
+      res.end(JSON.stringify({ errcode: 'M_TOO_LARGE', error: 'request body too large' }));
+      req.destroy();
+      return;
+    }
+    chunks.push(chunk);
+  });
+  req.on('end', () => {
+    if (rejected) return;
+    void (async () => {
+      const url = new URL(req.url ?? '/', 'http://localhost');
+      let body: unknown;
+      try {
+        const raw = Buffer.concat(chunks).toString();
+        body = raw ? JSON.parse(raw) : undefined;
+      } catch {
+        res.writeHead(400, { 'Content-Type': 'application/json' });
+        res.end(JSON.stringify({ errcode: 'M_NOT_JSON', error: 'invalid json' }));
+        return;
+      }
+      const result = await daemon.handle({
+        method: req.method ?? 'GET',
+        path: url.pathname,
+        searchParams: url.searchParams,
+        authorizationHeader: req.headers.authorization,
+        body,
+      });
+      res.writeHead(result.status, { 'Content-Type': 'application/json' });
+      res.end(JSON.stringify(result.body));
+    })().catch((error: unknown) => {
+      console.error('request failed:', error);
+      if (res.headersSent) {
+        res.destroy();
+        return;
+      }
+      res.writeHead(500, { 'Content-Type': 'application/json' });
+      res.end(JSON.stringify({ error: 'internal error' }));
+    });
+  });
+});
+
+server.listen(cfg.port, () => {
+  console.log(
+    `mosaic-as listening on :${cfg.port} (homeserver ${cfg.homeserverUrl}, domain ${cfg.domain})`,
+  );
+  if (cfg.bridgeTokens.length === 0) {
+    console.warn('WARNING: MOSAIC_AS_BRIDGE_TOKENS is empty — bridge API will deny all requests');
+  }
+});
diff --git a/apps/appservice/src/registration-main.ts b/apps/appservice/src/registration-main.ts
new file mode 100644
index 0000000..bf7ec8c
--- /dev/null
+++ b/apps/appservice/src/registration-main.ts
@@ -0,0 +1,10 @@
+import { buildRegistration, registrationToYaml } from '@mosaicstack/appservice';
+
+import { configFromEnv } from './config.js';
+
+// Prints the Synapse registration YAML (mosaic-as.yaml) for the current env.
+// Usage: MOSAIC_AS_URL=http://mosaic-as:8008 mosaic-as-registration > mosaic-as.yaml
+const cfg = configFromEnv();
+const url = process.env.MOSAIC_AS_URL;
+if (!url) throw new Error('missing required env var MOSAIC_AS_URL');
+process.stdout.write(registrationToYaml(buildRegistration(cfg, { url })));
diff --git a/apps/appservice/src/server.ts b/apps/appservice/src/server.ts
new file mode 100644
index 0000000..cff0e6c
--- /dev/null
+++ b/apps/appservice/src/server.ts
@@ -0,0 +1,124 @@
+import { createHmac, randomBytes, timingSafeEqual } from 'node:crypto';
+
+import {
+  AppserviceIntent,
+  TransactionHandler,
+  validateBridgeMessage,
+  validateBridgeTyping,
+} from '@mosaicstack/appservice';
+import type { AppserviceConfig, MatrixEvent } from '@mosaicstack/appservice';
+
+export interface DaemonConfig extends AppserviceConfig {
+  /** Bearer tokens accepted on /bridge/v1/* (one per agent-comms host daemon). */
+  bridgeTokens: string[];
+}
+
+export interface DaemonRequest {
+  method: string;
+  /** URL path without query string. */
+  path: string;
+  searchParams: URLSearchParams;
+  authorizationHeader?: string;
+  body: unknown;
+}
+
+export interface DaemonResponse {
+  status: number;
+  body: Record<string, unknown>;
+}
+
+// Compare equal-length HMAC digests so neither content nor LENGTH of the
+// stored secret is observable through timing.
+const HMAC_KEY = randomBytes(32);
+const digest = (value: string): Buffer => createHmac('sha256', HMAC_KEY).update(value).digest();
+
+const safeEqual = (a: string, b: string): boolean => timingSafeEqual(digest(a), digest(b));
+
+const TXN_PATH = /^\/_matrix\/app\/v1\/transactions\/([^/]+)$/;
+
+/**
+ * HTTP-framework-agnostic request router for the mosaic-as daemon: the
+ * Application Service transactions endpoint (Synapse-facing) plus the
+ * internal bridge API v1 (agent-comms daemon-facing). main.ts binds this to
+ * node:http; tests drive it directly.
+ */
+export class AppserviceDaemon {
+  readonly intent: AppserviceIntent;
+  private readonly transactions: TransactionHandler;
+
+  constructor(
+    private readonly cfg: DaemonConfig,
+    fetchImpl?: typeof fetch,
+    private readonly log: (line: string) => void = (line) => console.log(line),
+  ) {
+    this.intent = new AppserviceIntent(cfg, fetchImpl);
+    this.transactions = new TransactionHandler({
+      hsToken: cfg.hsToken,
+      onEvent: (event) => this.onEvent(event),
+      onError: (error, txnId) => this.log(`txn ${txnId} handler error: ${String(error)}`),
+    });
+  }
+
+  /** v1: the daemon only observes; room logic lives in the agent-comms daemons. */
+  private onEvent(event: MatrixEvent): void {
+    if (event.type === 'm.room.message') {
+      this.log(
+        `event ${event.event_id ?? '?'} in ${event.room_id ?? '?'} from ${event.sender ?? '?'}`,
+      );
+    }
+  }
+
+  private bridgeAuthorized(authorizationHeader: string | undefined): boolean {
+    if (!authorizationHeader?.startsWith('Bearer ')) return false;
+    const presented = authorizationHeader.slice('Bearer '.length);
+    return this.cfg.bridgeTokens.some((token) => safeEqual(presented, token));
+  }
+
+  async handle(req: DaemonRequest): Promise<DaemonResponse> {
+    if (req.method === 'GET' && req.path === '/health') {
+      return { status: 200, body: { ok: true } };
+    }
+
+    const txnMatch = req.method === 'PUT' ? TXN_PATH.exec(req.path) : null;
+    if (txnMatch?.[1] !== undefined) {
+      return this.transactions.handle(txnMatch[1], req.body, {
+        authorizationHeader: req.authorizationHeader,
+        accessTokenParam: req.searchParams.get('access_token') ?? undefined,
+      });
+    }
+
+    if (req.path.startsWith('/bridge/v1/')) {
+      if (!this.bridgeAuthorized(req.authorizationHeader)) {
+        return { status: 403, body: { errcode: 'M_FORBIDDEN', error: 'bad bridge token' } };
+      }
+      try {
+        if (req.method === 'POST' && req.path === '/bridge/v1/messages') {
+          validateBridgeMessage(req.body);
+          const eventId = await this.intent.sendAsAgent({
+            roomId: req.body.room_id,
+            agent: req.body.agent,
+            body: req.body.body,
+            threadRoot: req.body.thread_root,
+            msgtype: req.body.msgtype,
+            extraContent: req.body.extra_content,
+          });
+          return { status: 200, body: { event_id: eventId ?? null } };
+        }
+        if (req.method === 'POST' && req.path === '/bridge/v1/typing') {
+          validateBridgeTyping(req.body);
+          await this.intent.setTyping(req.body.room_id, req.body.agent, req.body.typing);
+          return { status: 200, body: {} };
+        }
+      } catch (error) {
+        const message = error instanceof Error ? error.message : String(error);
+        this.log(`bridge error ${req.method} ${req.path}: ${message}`);
+        return { status: 400, body: { error: message } };
+      }
+      // Explicit: never fall out of the authenticated bridge block, so future
+      // sub-paths cannot accidentally route around the auth guard above.
+      return { status: 405, body: { error: 'unsupported bridge method/path' } };
+    }
+
+    return { status: 404, body: { error: 'not found' } };
+  }
+}
diff --git a/apps/appservice/tsconfig.json b/apps/appservice/tsconfig.json
new file mode 100644
index 0000000..c973386
--- /dev/null
+++ b/apps/appservice/tsconfig.json
@@ -0,0 +1,9 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "dist",
+    "rootDir": "src"
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist"]
+}
diff --git a/docker/appservice.Dockerfile b/docker/appservice.Dockerfile
new file mode 100644
index 0000000..a92e252
--- /dev/null
+++ b/docker/appservice.Dockerfile
@@ -0,0 +1,28 @@
+FROM node:22-alpine AS base
+ENV PNPM_HOME="/pnpm"
+ENV PATH="$PNPM_HOME:$PATH"
+RUN corepack enable
+
+FROM base AS builder
+WORKDIR /app
+# Copy workspace manifests first for layer-cached install
+COPY pnpm-workspace.yaml pnpm-lock.yaml package.json ./
+COPY apps/appservice/package.json ./apps/appservice/
+COPY packages/ ./packages/
+COPY plugins/ ./plugins/
+RUN pnpm install --frozen-lockfile
+COPY . .
+RUN pnpm turbo run build --filter @mosaicstack/mosaic-as...
+RUN pnpm --filter @mosaicstack/mosaic-as --prod deploy --legacy /deploy
+
+FROM base AS runner
+WORKDIR /app
+ENV NODE_ENV=production
+COPY --from=builder /deploy/node_modules ./node_modules
+COPY --from=builder /deploy/package.json ./package.json
+COPY --from=builder /app/apps/appservice/dist ./dist
+USER node
+EXPOSE 8008
+HEALTHCHECK --interval=30s --timeout=5s --start-period=15s --retries=5 \
+  CMD ["node", "-e", "require('http').get('http://127.0.0.1:8008/health',r=>process.exit(r.statusCode===200?0:1)).on('error',()=>process.exit(1))"]
+CMD ["node", "dist/main.js"]
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index acab223..6132a4d 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -39,6 +39,25 @@ importers:
         specifier: ^2.0.0
         version: 2.1.9(@types/node@24.12.0)(jsdom@29.0.0(@noble/hashes@2.0.1))(lightningcss@1.31.1)
 
+  apps/appservice:
+    dependencies:
+      '@mosaicstack/appservice':
+        specifier: workspace:*
+        version: link:../../packages/appservice
+    devDependencies:
+      '@types/node':
+        specifier: ^22.0.0
+        version: 22.19.15
+      tsx:
+        specifier: ^4.19.0
+        version: 4.21.0
+      typescript:
+        specifier: ^5.8.0
+        version: 5.9.3
+      vitest:
+        specifier: ^2.0.0
+        version: 2.1.9(@types/node@22.19.15)(jsdom@29.0.0(@noble/hashes@2.0.1))(lightningcss@1.31.1)
+
   apps/gateway:
     dependencies:
       '@anthropic-ai/sdk':