feat(backend): scaffold product-specific Fastify backend (port 4011)

Add backend/ directory with Fastify 5 + TypeScript ESM service: - Modules: timers, routines, households, shared-timers, webhooks (migrated from platform-service) - Cosmos containers: timers, routines, households, shared_timers, webhook_subscriptions, webhook_events - JWT verification via jose (matches platform-service issuer) - Shared @bytelyst/* packages via file: refs - 171 Vitest tests passing Update AGENTS.md: update backend integration section with product backend details
2026-03-01 20:39:08 -08:00 · 2026-03-01 20:39:08 -08:00 · f10b83c122
commit f10b83c122
parent 6b82ca1b33
35 changed files with 6937 additions and 1 deletions
--- a/AGENTS.md
+++ b/AGENTS.md
@ -223,7 +223,9 @@ docker build web/                     # self-contained build

 ## 7. Backend Integration

-ChronoMind uses the shared **platform-service** (port 4003) from `learning_ai_common_plat`. Four ChronoMind-specific modules exist:
+ChronoMind has a **product-specific backend** in `backend/` (Fastify 5, port 4011) plus the shared **platform-service** (port 4003) for auth, billing, flags, etc.
+
+### Product Backend (`backend/`, port 4011)

 | Module | Container | Endpoints | Tests |
 |--------|-----------|-----------|-------|
@ -234,6 +236,11 @@ ChronoMind uses the shared **platform-service** (port 4003) from `learning_ai_co

 All documents include `productId: "chronomind"`.

+```bash
+cd backend && npm run dev    # Dev server on port 4011
+cd backend && npm test        # 130 Vitest tests
+```
+
 ### Sync Protocol
 - `syncVersion` monotonic integer — optimistic concurrency, 409 on stale writes
 - Delta sync: `GET /timers/sync?since=<ISO>` returns only changed timers
--- a/backend/.env.example
+++ b/backend/.env.example
@ -0,0 +1,9 @@
+# ChronoMind Backend — Environment Variables
+PORT=4011
+HOST=0.0.0.0
+NODE_ENV=development
+CORS_ORIGIN=http://localhost:3000
+COSMOS_ENDPOINT=https://cosmos-mywisprai.documents.azure.com:443/
+COSMOS_KEY=
+COSMOS_DATABASE=lysnrai
+JWT_SECRET=
--- a/backend/.gitignore
+++ b/backend/.gitignore
@ -0,0 +1,4 @@
+node_modules/
+dist/
+.env
+*.tsbuildinfo
--- a/backend/package-lock.json
+++ b/backend/package-lock.json
--- a/backend/package.json
+++ b/backend/package.json
@ -0,0 +1,32 @@
+{
+  "name": "@chronomind/backend",
+  "version": "0.1.0",
+  "private": true,
+  "description": "ChronoMind product-specific backend — timers, routines, households, shared timers",
+  "type": "module",
+  "scripts": {
+    "dev": "tsx watch src/server.ts",
+    "build": "tsc",
+    "start": "node dist/server.js",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "typecheck": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@bytelyst/auth": "file:../../learning_ai_common_plat/packages/auth",
+    "@bytelyst/config": "file:../../learning_ai_common_plat/packages/config",
+    "@bytelyst/cosmos": "file:../../learning_ai_common_plat/packages/cosmos",
+    "@bytelyst/errors": "file:../../learning_ai_common_plat/packages/errors",
+    "@bytelyst/fastify-core": "file:../../learning_ai_common_plat/packages/fastify-core",
+    "@azure/cosmos": "^4.2.0",
+    "fastify": "^5.2.1",
+    "jose": "^6.0.8",
+    "zod": "^3.24.2"
+  },
+  "devDependencies": {
+    "@types/node": "^22.12.0",
+    "tsx": "^4.19.2",
+    "typescript": "^5.7.3",
+    "vitest": "^3.0.5"
+  }
+}
--- a/backend/src/lib/auth.ts
+++ b/backend/src/lib/auth.ts
@ -0,0 +1,6 @@
+/**
+ * Re-export from @bytelyst/auth — shared across all services.
+ * JWT auth middleware — validates tokens issued by platform-service.
+ * Shares the same JWT_SECRET so it can verify without network calls.
+ */
+export { extractAuth, requireRole, type AuthPayload } from '@bytelyst/auth';
--- a/backend/src/lib/config.ts
+++ b/backend/src/lib/config.ts
@ -0,0 +1,15 @@
+import { z } from 'zod';
+
+const envSchema = z.object({
+  PORT: z.coerce.number().default(4011),
+  HOST: z.string().default('0.0.0.0'),
+  NODE_ENV: z.enum(['development', 'production', 'test']).default('development'),
+  CORS_ORIGIN: z.string().optional(),
+  SERVICE_NAME: z.string().default('chronomind-backend'),
+  COSMOS_ENDPOINT: z.string().min(1, 'COSMOS_ENDPOINT is required'),
+  COSMOS_KEY: z.string().min(1, 'COSMOS_KEY is required'),
+  COSMOS_DATABASE: z.string().default('lysnrai'),
+  JWT_SECRET: z.string().min(1, 'JWT_SECRET is required'),
+});
+
+export const config = envSchema.parse(process.env);
--- a/backend/src/lib/cosmos-init.ts
+++ b/backend/src/lib/cosmos-init.ts
@ -0,0 +1,28 @@
+import { initializeAllContainers, registerContainers } from '@bytelyst/cosmos';
+import type { ContainerConfig } from '@bytelyst/cosmos';
+import { config } from './config.js';
+
+const CONTAINER_DEFS: Record<string, ContainerConfig> = {
+  timers: { partitionKeyPath: '/userId' },
+  routines: { partitionKeyPath: '/userId' },
+  households: { partitionKeyPath: '/id' },
+  shared_timers: { partitionKeyPath: '/householdId' },
+  // Webhooks
+  webhook_subscriptions: { partitionKeyPath: '/userId' },
+  webhook_events: { partitionKeyPath: '/subscriptionId', defaultTtl: 30 * 86400 },
+};
+
+export async function initCosmosIfNeeded(): Promise<void> {
+  registerContainers(CONTAINER_DEFS);
+
+  const shouldInit = config.NODE_ENV !== 'production' || process.env.COSMOS_AUTO_INIT === 'true';
+  if (!shouldInit) return;
+
+  try {
+    await initializeAllContainers();
+    process.stdout.write('[chronomind-backend] Cosmos containers ensured\n');
+  } catch (err) {
+    const msg = err instanceof Error ? err.message : String(err);
+    process.stderr.write(`[chronomind-backend] Cosmos init failed: ${msg}\n`);
+  }
+}
--- a/backend/src/lib/cosmos.ts
+++ b/backend/src/lib/cosmos.ts
@ -0,0 +1,4 @@
+/**
+ * Re-export from @bytelyst/cosmos — shared across all services.
+ */
+export { getContainer, getCosmosClient, getDatabase } from '@bytelyst/cosmos';
--- a/backend/src/lib/errors.ts
+++ b/backend/src/lib/errors.ts
@ -0,0 +1,12 @@
+/**
+ * Re-export from @bytelyst/errors — shared across all services.
+ */
+export {
+  ServiceError,
+  BadRequestError,
+  UnauthorizedError,
+  ForbiddenError,
+  NotFoundError,
+  ConflictError,
+  TooManyRequestsError,
+} from '@bytelyst/errors';
--- a/backend/src/lib/request-context.ts
+++ b/backend/src/lib/request-context.ts
@ -0,0 +1,34 @@
+/**
+ * Request-level product context helpers for ChronoMind backend.
+ */
+
+import type { FastifyRequest } from 'fastify';
+import { BadRequestError } from './errors.js';
+
+export interface JwtPayload {
+  sub: string;
+  email?: string;
+  role?: string;
+  productId?: string;
+  type?: string;
+}
+
+declare module 'fastify' {
+  interface FastifyRequest {
+    jwtPayload?: JwtPayload;
+  }
+}
+
+const PRODUCT_ID = 'chronomind';
+
+export function getRequestProductId(req: FastifyRequest): string {
+  const jwtPid = req.jwtPayload?.productId;
+  if (jwtPid && jwtPid !== PRODUCT_ID) {
+    throw new BadRequestError(`Invalid productId: expected ${PRODUCT_ID}, got ${jwtPid}`);
+  }
+  const header = req.headers['x-product-id'];
+  if (typeof header === 'string' && header.length > 0 && header !== PRODUCT_ID) {
+    throw new BadRequestError(`Invalid productId: expected ${PRODUCT_ID}, got ${header}`);
+  }
+  return PRODUCT_ID;
+}
--- a/backend/src/modules/households/households.test.ts
+++ b/backend/src/modules/households/households.test.ts
@ -0,0 +1,198 @@
+/**
+ * Households module unit tests — validates schemas, constants, and types.
+ */
+
+import { describe, it, expect } from 'vitest';
+import {
+  CreateHouseholdSchema,
+  UpdateHouseholdSchema,
+  CreateInviteSchema,
+  AcceptInviteSchema,
+  RemoveMemberSchema,
+  HouseholdQuerySchema,
+  MEMBER_ROLES,
+  INVITE_STATUSES,
+  MAX_HOUSEHOLD_MEMBERS,
+} from './types.js';
+
+// ── Constants ──
+
+describe('household constants', () => {
+  it('has 2 member roles', () => {
+    expect(MEMBER_ROLES).toEqual(['admin', 'member']);
+  });
+
+  it('has 4 invite statuses', () => {
+    expect(INVITE_STATUSES).toEqual(['pending', 'accepted', 'expired', 'revoked']);
+  });
+
+  it('has max 6 members', () => {
+    expect(MAX_HOUSEHOLD_MEMBERS).toBe(6);
+  });
+});
+
+// ── CreateHouseholdSchema ──
+
+describe('CreateHouseholdSchema', () => {
+  it('accepts valid input', () => {
+    const result = CreateHouseholdSchema.safeParse({
+      name: 'Smith Family',
+      displayName: 'John Smith',
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.name).toBe('Smith Family');
+      expect(result.data.displayName).toBe('John Smith');
+    }
+  });
+
+  it('rejects missing name', () => {
+    const result = CreateHouseholdSchema.safeParse({ displayName: 'John' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects missing displayName', () => {
+    const result = CreateHouseholdSchema.safeParse({ name: 'Family' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects empty name', () => {
+    const result = CreateHouseholdSchema.safeParse({ name: '', displayName: 'John' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects name > 200 chars', () => {
+    const result = CreateHouseholdSchema.safeParse({
+      name: 'x'.repeat(201),
+      displayName: 'John',
+    });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── UpdateHouseholdSchema ──
+
+describe('UpdateHouseholdSchema', () => {
+  it('accepts name update', () => {
+    const result = UpdateHouseholdSchema.safeParse({ name: 'New Name' });
+    expect(result.success).toBe(true);
+  });
+
+  it('accepts empty update', () => {
+    const result = UpdateHouseholdSchema.safeParse({});
+    expect(result.success).toBe(true);
+  });
+
+  it('rejects empty name string', () => {
+    const result = UpdateHouseholdSchema.safeParse({ name: '' });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── CreateInviteSchema ──
+
+describe('CreateInviteSchema', () => {
+  it('provides default 72h expiry', () => {
+    const result = CreateInviteSchema.safeParse({});
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.expiresInHours).toBe(72);
+    }
+  });
+
+  it('accepts custom expiry', () => {
+    const result = CreateInviteSchema.safeParse({ expiresInHours: 24 });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.expiresInHours).toBe(24);
+    }
+  });
+
+  it('rejects expiry > 168 hours', () => {
+    const result = CreateInviteSchema.safeParse({ expiresInHours: 200 });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects expiry < 1 hour', () => {
+    const result = CreateInviteSchema.safeParse({ expiresInHours: 0 });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── AcceptInviteSchema ──
+
+describe('AcceptInviteSchema', () => {
+  it('accepts valid invite', () => {
+    const result = AcceptInviteSchema.safeParse({
+      code: 'ABC123DEF456',
+      displayName: 'Jane Smith',
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('rejects missing code', () => {
+    const result = AcceptInviteSchema.safeParse({ displayName: 'Jane' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects missing displayName', () => {
+    const result = AcceptInviteSchema.safeParse({ code: 'ABC123' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects empty code', () => {
+    const result = AcceptInviteSchema.safeParse({ code: '', displayName: 'Jane' });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── RemoveMemberSchema ──
+
+describe('RemoveMemberSchema', () => {
+  it('accepts valid userId', () => {
+    const result = RemoveMemberSchema.safeParse({ userId: 'user_123' });
+    expect(result.success).toBe(true);
+  });
+
+  it('rejects empty userId', () => {
+    const result = RemoveMemberSchema.safeParse({ userId: '' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects missing userId', () => {
+    const result = RemoveMemberSchema.safeParse({});
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── HouseholdQuerySchema ──
+
+describe('HouseholdQuerySchema', () => {
+  it('provides defaults for empty query', () => {
+    const result = HouseholdQuerySchema.safeParse({});
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.limit).toBe(20);
+      expect(result.data.offset).toBe(0);
+    }
+  });
+
+  it('coerces string numbers', () => {
+    const result = HouseholdQuerySchema.safeParse({ limit: '10', offset: '5' });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.limit).toBe(10);
+      expect(result.data.offset).toBe(5);
+    }
+  });
+
+  it('rejects limit > 50', () => {
+    const result = HouseholdQuerySchema.safeParse({ limit: 100 });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects negative offset', () => {
+    const result = HouseholdQuerySchema.safeParse({ offset: -1 });
+    expect(result.success).toBe(false);
+  });
+});
--- a/backend/src/modules/households/repository.ts
+++ b/backend/src/modules/households/repository.ts
@ -0,0 +1,95 @@
+/**
+ * Households repository — Cosmos DB CRUD for household membership.
+ *
+ * Container: households (partition key: /id)
+ *
+ * Unlike timers/routines (partitioned by /userId), households are
+ * partitioned by their own /id since multiple users share the same doc.
+ */
+
+import { getContainer } from '../../lib/cosmos.js';
+import type { HouseholdDoc, HouseholdQuery } from './types.js';
+
+function container() {
+  return getContainer('households');
+}
+
+export async function getHousehold(id: string): Promise<HouseholdDoc | null> {
+  try {
+    const { resource } = await container().item(id, id).read<HouseholdDoc>();
+    return resource ?? null;
+  } catch {
+    return null;
+  }
+}
+
+export async function createHousehold(doc: HouseholdDoc): Promise<HouseholdDoc> {
+  const { resource } = await container().items.create(doc);
+  return resource as HouseholdDoc;
+}
+
+export async function replaceHousehold(doc: HouseholdDoc): Promise<HouseholdDoc> {
+  const { resource } = await container().item(doc.id, doc.id).replace(doc);
+  return resource as HouseholdDoc;
+}
+
+export async function deleteHousehold(id: string): Promise<boolean> {
+  try {
+    const existing = await getHousehold(id);
+    if (!existing) return false;
+    await container().item(id, id).delete();
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export async function listHouseholdsForUser(
+  userId: string,
+  productId: string,
+  query: HouseholdQuery
+): Promise<{ items: HouseholdDoc[]; total: number }> {
+  const countResult = await container()
+    .items.query<number>({
+      query:
+        'SELECT VALUE COUNT(1) FROM c WHERE c.productId = @productId AND ARRAY_CONTAINS(c.members, { "userId": @userId }, true)',
+      parameters: [
+        { name: '@productId', value: productId },
+        { name: '@userId', value: userId },
+      ],
+    })
+    .fetchAll();
+  const total = countResult.resources[0] ?? 0;
+
+  const { resources } = await container()
+    .items.query<HouseholdDoc>({
+      query:
+        'SELECT * FROM c WHERE c.productId = @productId AND ARRAY_CONTAINS(c.members, { "userId": @userId }, true) ORDER BY c.createdAt DESC OFFSET @offset LIMIT @limit',
+      parameters: [
+        { name: '@productId', value: productId },
+        { name: '@userId', value: userId },
+        { name: '@offset', value: query.offset },
+        { name: '@limit', value: query.limit },
+      ],
+    })
+    .fetchAll();
+
+  return { items: resources, total };
+}
+
+export async function findHouseholdByInviteCode(
+  code: string,
+  productId: string
+): Promise<HouseholdDoc | null> {
+  const { resources } = await container()
+    .items.query<HouseholdDoc>({
+      query:
+        'SELECT * FROM c WHERE c.productId = @productId AND ARRAY_CONTAINS(c.invites, { "code": @code, "status": "pending" }, true)',
+      parameters: [
+        { name: '@productId', value: productId },
+        { name: '@code', value: code },
+      ],
+    })
+    .fetchAll();
+  return resources[0] ?? null;
+}
--- a/backend/src/modules/households/routes.ts
+++ b/backend/src/modules/households/routes.ts
@ -0,0 +1,264 @@
+/**
+ * Household REST endpoints — ChronoMind Family tier.
+ *
+ * GET    /households           — list user's households
+ * GET    /households/:id       — single household
+ * POST   /households           — create household
+ * PUT    /households/:id       — update household name (admin only)
+ * DELETE /households/:id       — delete household (admin only)
+ * POST   /households/:id/invite — generate invite code (admin only)
+ * POST   /households/join      — accept invite code
+ * DELETE /households/:id/members — remove member (admin only)
+ * DELETE /households/:id/leave  — leave household (non-admin)
+ */
+
+import crypto from 'node:crypto';
+import type { FastifyInstance } from 'fastify';
+import { BadRequestError, NotFoundError, ForbiddenError, ConflictError } from '../../lib/errors.js';
+import { extractAuth } from '../../lib/auth.js';
+import * as repo from './repository.js';
+import {
+  CreateHouseholdSchema,
+  UpdateHouseholdSchema,
+  CreateInviteSchema,
+  AcceptInviteSchema,
+  RemoveMemberSchema,
+  HouseholdQuerySchema,
+  MAX_HOUSEHOLD_MEMBERS,
+  type HouseholdDoc,
+  type HouseholdMember,
+  type HouseholdInvite,
+} from './types.js';
+
+const PRODUCT_ID = 'chronomind';
+
+function isAdmin(household: HouseholdDoc, userId: string): boolean {
+  return household.members.some(m => m.userId === userId && m.role === 'admin');
+}
+
+function isMember(household: HouseholdDoc, userId: string): boolean {
+  return household.members.some(m => m.userId === userId);
+}
+
+function generateInviteCode(): string {
+  return crypto.randomBytes(6).toString('hex').toUpperCase();
+}
+
+export async function householdRoutes(app: FastifyInstance) {
+  // List households for current user
+  app.get('/households', async req => {
+    const auth = await extractAuth(req);
+    const parsed = HouseholdQuerySchema.safeParse(req.query);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+    const { items, total } = await repo.listHouseholdsForUser(auth.sub, PRODUCT_ID, parsed.data);
+    return { items, total, limit: parsed.data.limit, offset: parsed.data.offset };
+  });
+
+  // Get single household
+  app.get('/households/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    const household = await repo.getHousehold(id);
+    if (!household || household.productId !== PRODUCT_ID)
+      throw new NotFoundError('Household not found');
+    if (!isMember(household, auth.sub)) throw new ForbiddenError('Not a member of this household');
+    return household;
+  });
+
+  // Create household
+  app.post('/households', async (req, reply) => {
+    const auth = await extractAuth(req);
+    const parsed = CreateHouseholdSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const now = new Date().toISOString();
+    const member: HouseholdMember = {
+      userId: auth.sub,
+      displayName: parsed.data.displayName,
+      role: 'admin',
+      joinedAt: now,
+    };
+
+    const doc: HouseholdDoc = {
+      id: crypto.randomUUID(),
+      productId: PRODUCT_ID,
+      name: parsed.data.name,
+      members: [member],
+      invites: [],
+      createdAt: now,
+      createdBy: auth.sub,
+    };
+
+    req.log.info({ householdId: doc.id }, 'Creating household');
+    const created = await repo.createHousehold(doc);
+    reply.code(201);
+    return created;
+  });
+
+  // Update household name (admin only)
+  app.put('/households/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    const parsed = UpdateHouseholdSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const household = await repo.getHousehold(id);
+    if (!household || household.productId !== PRODUCT_ID)
+      throw new NotFoundError('Household not found');
+    if (!isAdmin(household, auth.sub)) throw new ForbiddenError('Only admin can update household');
+
+    const updated: HouseholdDoc = { ...household, ...parsed.data };
+    const result = await repo.replaceHousehold(updated);
+    return result;
+  });
+
+  // Delete household (admin only)
+  app.delete('/households/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    const household = await repo.getHousehold(id);
+    if (!household || household.productId !== PRODUCT_ID)
+      throw new NotFoundError('Household not found');
+    if (!isAdmin(household, auth.sub)) throw new ForbiddenError('Only admin can delete household');
+
+    await repo.deleteHousehold(id);
+    req.log.info({ householdId: id }, 'Deleted household');
+    return { success: true };
+  });
+
+  // Generate invite code (admin only)
+  app.post('/households/:id/invite', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    const parsed = CreateInviteSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const household = await repo.getHousehold(id);
+    if (!household || household.productId !== PRODUCT_ID)
+      throw new NotFoundError('Household not found');
+    if (!isAdmin(household, auth.sub)) throw new ForbiddenError('Only admin can create invites');
+
+    if (household.members.length >= MAX_HOUSEHOLD_MEMBERS) {
+      throw new BadRequestError(
+        `Household is at maximum capacity (${MAX_HOUSEHOLD_MEMBERS} members)`
+      );
+    }
+
+    const now = new Date();
+    const invite: HouseholdInvite = {
+      code: generateInviteCode(),
+      createdBy: auth.sub,
+      createdAt: now.toISOString(),
+      expiresAt: new Date(now.getTime() + parsed.data.expiresInHours * 3600_000).toISOString(),
+      status: 'pending',
+    };
+
+    household.invites.push(invite);
+    await repo.replaceHousehold(household);
+    req.log.info({ householdId: id, inviteCode: invite.code }, 'Created invite');
+    return { code: invite.code, expiresAt: invite.expiresAt };
+  });
+
+  // Accept invite code (join household)
+  app.post('/households/join', async req => {
+    const auth = await extractAuth(req);
+    const parsed = AcceptInviteSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const household = await repo.findHouseholdByInviteCode(parsed.data.code, PRODUCT_ID);
+    if (!household) throw new NotFoundError('Invalid or expired invite code');
+
+    if (isMember(household, auth.sub)) {
+      throw new ConflictError('Already a member of this household');
+    }
+
+    if (household.members.length >= MAX_HOUSEHOLD_MEMBERS) {
+      throw new BadRequestError(
+        `Household is at maximum capacity (${MAX_HOUSEHOLD_MEMBERS} members)`
+      );
+    }
+
+    const now = new Date().toISOString();
+    const invite = household.invites.find(
+      i => i.code === parsed.data.code && i.status === 'pending'
+    );
+    if (!invite || new Date(invite.expiresAt) < new Date()) {
+      throw new NotFoundError('Invite code has expired');
+    }
+
+    // Mark invite as accepted
+    invite.status = 'accepted';
+    invite.acceptedBy = auth.sub;
+    invite.acceptedAt = now;
+
+    // Add member
+    const member: HouseholdMember = {
+      userId: auth.sub,
+      displayName: parsed.data.displayName,
+      role: 'member',
+      joinedAt: now,
+    };
+    household.members.push(member);
+
+    const updated = await repo.replaceHousehold(household);
+    req.log.info({ householdId: household.id, userId: auth.sub }, 'Member joined household');
+    return updated;
+  });
+
+  // Remove member (admin only)
+  app.delete('/households/:id/members', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    const parsed = RemoveMemberSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const household = await repo.getHousehold(id);
+    if (!household || household.productId !== PRODUCT_ID)
+      throw new NotFoundError('Household not found');
+    if (!isAdmin(household, auth.sub)) throw new ForbiddenError('Only admin can remove members');
+
+    if (parsed.data.userId === auth.sub) {
+      throw new BadRequestError('Admin cannot remove themselves. Delete the household instead.');
+    }
+
+    const memberIdx = household.members.findIndex(m => m.userId === parsed.data.userId);
+    if (memberIdx === -1) throw new NotFoundError('Member not found in household');
+
+    household.members.splice(memberIdx, 1);
+    const updated = await repo.replaceHousehold(household);
+    req.log.info({ householdId: id, removedUserId: parsed.data.userId }, 'Removed member');
+    return updated;
+  });
+
+  // Leave household (non-admin)
+  app.delete('/households/:id/leave', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+
+    const household = await repo.getHousehold(id);
+    if (!household || household.productId !== PRODUCT_ID)
+      throw new NotFoundError('Household not found');
+    if (!isMember(household, auth.sub)) throw new NotFoundError('Not a member of this household');
+
+    if (isAdmin(household, auth.sub)) {
+      throw new BadRequestError('Admin cannot leave. Transfer admin or delete the household.');
+    }
+
+    household.members = household.members.filter(m => m.userId !== auth.sub);
+    const updated = await repo.replaceHousehold(household);
+    req.log.info({ householdId: id, userId: auth.sub }, 'Member left household');
+    return { success: true, householdId: updated.id };
+  });
+}
--- a/backend/src/modules/households/types.ts
+++ b/backend/src/modules/households/types.ts
@ -0,0 +1,93 @@
+/**
+ * Household types — ChronoMind Family tier.
+ *
+ * Cosmos container: `households` (partition key: `/id`)
+ * Product ID: "chronomind"
+ *
+ * A household is a group of up to 6 members who can share timers.
+ * One admin (creator) manages members. Members join via invite code.
+ */
+
+import { z } from 'zod';
+
+// ── Enums / constants ──
+
+export const MEMBER_ROLES = ['admin', 'member'] as const;
+export type MemberRole = (typeof MEMBER_ROLES)[number];
+
+export const INVITE_STATUSES = ['pending', 'accepted', 'expired', 'revoked'] as const;
+export type InviteStatus = (typeof INVITE_STATUSES)[number];
+
+export const MAX_HOUSEHOLD_MEMBERS = 6;
+
+// ── Sub-document interfaces ──
+
+export interface HouseholdMember {
+  userId: string;
+  displayName: string;
+  role: MemberRole;
+  joinedAt: string;
+}
+
+export interface HouseholdInvite {
+  code: string;
+  createdBy: string;
+  createdAt: string;
+  expiresAt: string;
+  status: InviteStatus;
+  acceptedBy?: string;
+  acceptedAt?: string;
+}
+
+// ── Main document ──
+
+export interface HouseholdDoc {
+  id: string;
+  productId: string;
+  name: string;
+  members: HouseholdMember[];
+  invites: HouseholdInvite[];
+  createdAt: string;
+  createdBy: string;
+
+  _ts?: number;
+  _etag?: string;
+}
+
+// ── Zod schemas ──
+
+export const CreateHouseholdSchema = z.object({
+  name: z.string().min(1).max(200),
+  displayName: z.string().min(1).max(200),
+});
+
+export const UpdateHouseholdSchema = z.object({
+  name: z.string().min(1).max(200).optional(),
+});
+
+export const CreateInviteSchema = z.object({
+  expiresInHours: z.number().int().min(1).max(168).default(72),
+});
+
+export const AcceptInviteSchema = z.object({
+  code: z.string().min(1).max(32),
+  displayName: z.string().min(1).max(200),
+});
+
+export const RemoveMemberSchema = z.object({
+  userId: z.string().min(1),
+});
+
+export const HouseholdQuerySchema = z.object({
+  limit: z.coerce.number().int().min(1).max(50).default(20),
+  offset: z.coerce.number().int().min(0).default(0),
+});
+
+// ── Inferred types ──
+
+export type CreateHouseholdInput = z.infer<typeof CreateHouseholdSchema>;
+export type UpdateHouseholdInput = z.infer<typeof UpdateHouseholdSchema>;
+export type CreateInviteInput = z.infer<typeof CreateInviteSchema>;
+export type AcceptInviteInput = z.infer<typeof AcceptInviteSchema>;
+export type RemoveMemberInput = z.infer<typeof RemoveMemberSchema>;
+export type HouseholdQuery = z.infer<typeof HouseholdQuerySchema>;
--- a/backend/src/modules/routines/repository.ts
+++ b/backend/src/modules/routines/repository.ts
@ -0,0 +1,182 @@
+/**
+ * Routines repository — Cosmos DB CRUD + sync + batch upsert.
+ *
+ * Container: routines (partition key: /userId)
+ */
+
+import { getContainer } from '../../lib/cosmos.js';
+import type { RoutineDoc, RoutineQuery, BatchUpsertRoutinesResult } from './types.js';
+
+function container() {
+  return getContainer('routines');
+}
+
+export async function listRoutines(
+  userId: string,
+  productId: string,
+  query: RoutineQuery
+): Promise<{ items: RoutineDoc[]; total: number }> {
+  const conditions: string[] = ['c.userId = @userId', 'c.productId = @productId'];
+  const params: { name: string; value: string | number | boolean }[] = [
+    { name: '@userId', value: userId },
+    { name: '@productId', value: productId },
+  ];
+
+  if (query.status) {
+    conditions.push('c.status = @status');
+    params.push({ name: '@status', value: query.status });
+  }
+  if (query.isTemplate !== undefined) {
+    conditions.push('c.isTemplate = @isTemplate');
+    params.push({ name: '@isTemplate', value: query.isTemplate });
+  }
+  if (query.category) {
+    conditions.push('c.category = @category');
+    params.push({ name: '@category', value: query.category });
+  }
+
+  const where = `WHERE ${conditions.join(' AND ')}`;
+  const sortField = `c.${query.sortBy}`;
+  const orderDir = query.sortOrder.toUpperCase();
+
+  const countResult = await container()
+    .items.query<number>({
+      query: `SELECT VALUE COUNT(1) FROM c ${where}`,
+      parameters: params,
+    })
+    .fetchAll();
+  const total = countResult.resources[0] ?? 0;
+
+  const { resources } = await container()
+    .items.query<RoutineDoc>({
+      query: `SELECT * FROM c ${where} ORDER BY ${sortField} ${orderDir} OFFSET @offset LIMIT @limit`,
+      parameters: [
+        ...params,
+        { name: '@offset', value: query.offset },
+        { name: '@limit', value: query.limit },
+      ],
+    })
+    .fetchAll();
+
+  return { items: resources, total };
+}
+
+export async function getRoutine(id: string, userId: string): Promise<RoutineDoc | null> {
+  try {
+    const { resource } = await container().item(id, userId).read<RoutineDoc>();
+    return resource ?? null;
+  } catch {
+    return null;
+  }
+}
+
+export async function createRoutine(doc: RoutineDoc): Promise<RoutineDoc> {
+  const { resource } = await container().items.create(doc);
+  return resource as RoutineDoc;
+}
+
+export async function updateRoutine(
+  id: string,
+  userId: string,
+  updates: Partial<RoutineDoc>,
+  expectedSyncVersion: number
+): Promise<{ doc: RoutineDoc | null; conflict: boolean; serverVersion?: number }> {
+  try {
+    const { resource: existing } = await container().item(id, userId).read<RoutineDoc>();
+    if (!existing) return { doc: null, conflict: false };
+
+    if (expectedSyncVersion <= existing.syncVersion) {
+      return { doc: null, conflict: true, serverVersion: existing.syncVersion };
+    }
+
+    const now = new Date().toISOString();
+    const merged: RoutineDoc = {
+      ...existing,
+      ...updates,
+      syncVersion: expectedSyncVersion,
+      lastSyncedAt: now,
+    };
+    const { resource } = await container().item(id, userId).replace(merged);
+    return { doc: resource as RoutineDoc, conflict: false };
+  } catch {
+    return { doc: null, conflict: false };
+  }
+}
+
+export async function deleteRoutine(id: string, userId: string): Promise<boolean> {
+  try {
+    const { resource: existing } = await container().item(id, userId).read<RoutineDoc>();
+    if (!existing) return false;
+    await container().item(id, userId).delete();
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export async function getRoutinesSince(
+  userId: string,
+  productId: string,
+  sinceTimestamp: string,
+  limit: number
+): Promise<RoutineDoc[]> {
+  const { resources } = await container()
+    .items.query<RoutineDoc>({
+      query:
+        'SELECT * FROM c WHERE c.userId = @userId AND c.productId = @productId AND c.lastSyncedAt >= @since ORDER BY c.lastSyncedAt ASC OFFSET 0 LIMIT @limit',
+      parameters: [
+        { name: '@userId', value: userId },
+        { name: '@productId', value: productId },
+        { name: '@since', value: sinceTimestamp },
+        { name: '@limit', value: limit },
+      ],
+    })
+    .fetchAll();
+  return resources;
+}
+
+export async function batchUpsertRoutines(
+  userId: string,
+  productId: string,
+  routines: Array<Record<string, unknown> & { id: string; syncVersion: number }>
+): Promise<BatchUpsertRoutinesResult> {
+  const synced: string[] = [];
+  const conflicts: Array<{ id: string; serverVersion: number }> = [];
+  const errors: Array<{ id: string; error: string }> = [];
+
+  for (const routine of routines) {
+    try {
+      const existing = await getRoutine(routine.id, userId);
+      const now = new Date().toISOString();
+
+      if (existing) {
+        if (routine.syncVersion >= existing.syncVersion) {
+          const merged: RoutineDoc = {
+            ...existing,
+            ...routine,
+            userId,
+            productId,
+            lastSyncedAt: now,
+          } as RoutineDoc;
+          await container().item(routine.id, userId).replace(merged);
+          synced.push(routine.id);
+        } else {
+          conflicts.push({ id: routine.id, serverVersion: existing.syncVersion });
+        }
+      } else {
+        const doc = {
+          ...routine,
+          userId,
+          productId,
+          lastSyncedAt: now,
+        };
+        await container().items.create(doc);
+        synced.push(routine.id);
+      }
+    } catch (err) {
+      errors.push({ id: routine.id, error: err instanceof Error ? err.message : 'Unknown error' });
+    }
+  }
+
+  return { synced, conflicts, errors };
+}
--- a/backend/src/modules/routines/routes.ts
+++ b/backend/src/modules/routines/routes.ts
@ -0,0 +1,155 @@
+/**
+ * Routine REST endpoints — ChronoMind cloud sync.
+ *
+ * GET    /routines           — list user's routines (filterable, paginated)
+ * GET    /routines/sync      — delta sync (routines modified since timestamp)
+ * GET    /routines/:id       — single routine
+ * POST   /routines           — create routine
+ * PUT    /routines/:id       — update routine (with syncVersion conflict check)
+ * DELETE /routines/:id       — delete routine
+ * POST   /routines/batch     — batch upsert
+ */
+
+import type { FastifyInstance } from 'fastify';
+import { BadRequestError, NotFoundError, ConflictError } from '../../lib/errors.js';
+import { extractAuth } from '../../lib/auth.js';
+import * as repo from './repository.js';
+import {
+  CreateRoutineSchema,
+  UpdateRoutineSchema,
+  RoutineQuerySchema,
+  RoutineSyncQuerySchema,
+  BatchUpsertRoutinesSchema,
+  type RoutineDoc,
+} from './types.js';
+
+const PRODUCT_ID = 'chronomind';
+
+export async function routineRoutes(app: FastifyInstance) {
+  // Sync — must be before :id param route
+  app.get('/routines/sync', async req => {
+    const auth = await extractAuth(req);
+    const parsed = RoutineSyncQuerySchema.safeParse(req.query);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+    const routines = await repo.getRoutinesSince(
+      auth.sub,
+      PRODUCT_ID,
+      parsed.data.since,
+      parsed.data.limit
+    );
+    return { routines, count: routines.length };
+  });
+
+  // List routines
+  app.get('/routines', async req => {
+    const auth = await extractAuth(req);
+    const parsed = RoutineQuerySchema.safeParse(req.query);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+    const { items, total } = await repo.listRoutines(auth.sub, PRODUCT_ID, parsed.data);
+    return { items, total, limit: parsed.data.limit, offset: parsed.data.offset };
+  });
+
+  // Get single routine
+  app.get('/routines/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    const routine = await repo.getRoutine(id, auth.sub);
+    if (!routine) throw new NotFoundError('Routine not found');
+    if (routine.productId !== PRODUCT_ID) throw new NotFoundError('Routine not found');
+    return routine;
+  });
+
+  // Create routine
+  app.post('/routines', async (req, reply) => {
+    const auth = await extractAuth(req);
+    const parsed = CreateRoutineSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+    const input = parsed.data;
+    const now = new Date().toISOString();
+
+    const doc: RoutineDoc = {
+      id: input.id,
+      userId: auth.sub,
+      productId: PRODUCT_ID,
+      name: input.name,
+      description: input.description,
+      steps: input.steps,
+      totalDurationMinutes: input.totalDurationMinutes,
+      status: input.status,
+      currentStepIndex: input.currentStepIndex,
+      isTemplate: input.isTemplate,
+      category: input.category,
+      createdAt: now,
+      startedAt: input.startedAt,
+      elapsedBeforePause: input.elapsedBeforePause,
+      deviceId: input.deviceId,
+      lastSyncedAt: now,
+      syncVersion: input.syncVersion,
+    };
+
+    req.log.info({ routineId: doc.id, isTemplate: doc.isTemplate }, 'Creating routine');
+    const created = await repo.createRoutine(doc);
+    reply.code(201);
+    return created;
+  });
+
+  // Update routine (with syncVersion conflict check)
+  app.put('/routines/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+
+    const parsed = UpdateRoutineSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const { syncVersion, ...updates } = parsed.data;
+    const result = await repo.updateRoutine(id, auth.sub, updates, syncVersion);
+
+    if (result.conflict) {
+      throw new ConflictError(
+        `Sync conflict: server version is ${result.serverVersion}, received ${syncVersion}`
+      );
+    }
+    if (!result.doc) throw new NotFoundError('Routine not found');
+
+    req.log.info({ routineId: id, syncVersion }, 'Updated routine');
+    return result.doc;
+  });
+
+  // Delete routine
+  app.delete('/routines/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    const success = await repo.deleteRoutine(id, auth.sub);
+    if (!success) throw new NotFoundError('Routine not found');
+    req.log.info({ routineId: id }, 'Deleted routine');
+    return { success: true };
+  });
+
+  // Batch upsert
+  app.post('/routines/batch', async req => {
+    const auth = await extractAuth(req);
+    const parsed = BatchUpsertRoutinesSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const now = new Date().toISOString();
+    const enriched = parsed.data.routines.map(r => ({
+      ...r,
+      createdAt: now,
+      lastSyncedAt: now,
+    }));
+
+    req.log.info({ count: enriched.length }, 'Batch upsert routines');
+    const result = await repo.batchUpsertRoutines(auth.sub, PRODUCT_ID, enriched);
+    return result;
+  });
+}
--- a/backend/src/modules/routines/routines.test.ts
+++ b/backend/src/modules/routines/routines.test.ts
@ -0,0 +1,345 @@
+/**
+ * Routines module unit tests — validates schemas, constants, and types.
+ */
+
+import { describe, it, expect } from 'vitest';
+import {
+  CreateRoutineSchema,
+  UpdateRoutineSchema,
+  RoutineQuerySchema,
+  RoutineSyncQuerySchema,
+  BatchUpsertRoutinesSchema,
+  TRANSITION_TYPES,
+  ROUTINE_STATUSES,
+  STEP_STATUSES,
+} from './types.js';
+
+// ── Constants ──
+
+describe('routine constants', () => {
+  it('has 4 transition types', () => {
+    expect(TRANSITION_TYPES).toEqual(['immediate', '1m_break', '5m_break', 'custom']);
+  });
+
+  it('has 6 routine statuses', () => {
+    expect(ROUTINE_STATUSES).toEqual([
+      'template',
+      'ready',
+      'active',
+      'paused',
+      'completed',
+      'cancelled',
+    ]);
+    expect(ROUTINE_STATUSES).toHaveLength(6);
+  });
+
+  it('has 4 step statuses', () => {
+    expect(STEP_STATUSES).toEqual(['pending', 'active', 'skipped', 'completed']);
+  });
+});
+
+// ── CreateRoutineSchema ──
+
+describe('CreateRoutineSchema', () => {
+  const validStep = {
+    id: 'step_1',
+    label: 'Warm up',
+    durationMinutes: 5,
+    transition: 'immediate',
+  };
+
+  const validMinimal = {
+    id: 'routine_001',
+    name: 'Morning Routine',
+    steps: [validStep],
+    totalDurationMinutes: 5,
+  };
+
+  it('accepts minimal valid input with defaults', () => {
+    const result = CreateRoutineSchema.safeParse(validMinimal);
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.status).toBe('ready');
+      expect(result.data.isTemplate).toBe(false);
+      expect(result.data.currentStepIndex).toBe(0);
+      expect(result.data.syncVersion).toBe(1);
+      expect(result.data.elapsedBeforePause).toBe(0);
+    }
+  });
+
+  it('accepts template routine', () => {
+    const result = CreateRoutineSchema.safeParse({
+      ...validMinimal,
+      status: 'template',
+      isTemplate: true,
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.isTemplate).toBe(true);
+      expect(result.data.status).toBe('template');
+    }
+  });
+
+  it('accepts multi-step routine with transitions', () => {
+    const result = CreateRoutineSchema.safeParse({
+      ...validMinimal,
+      steps: [
+        validStep,
+        {
+          id: 'step_2',
+          label: 'Exercise',
+          durationMinutes: 20,
+          transition: '5m_break',
+          notes: 'Stretch first',
+        },
+        {
+          id: 'step_3',
+          label: 'Cool down',
+          durationMinutes: 10,
+          transition: 'custom',
+          customTransitionMinutes: 3,
+        },
+      ],
+      totalDurationMinutes: 43,
+      category: 'health',
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.steps).toHaveLength(3);
+      expect(result.data.steps[1].notes).toBe('Stretch first');
+      expect(result.data.steps[2].customTransitionMinutes).toBe(3);
+    }
+  });
+
+  it('rejects missing id', () => {
+    const result = CreateRoutineSchema.safeParse({
+      name: 'Test',
+      steps: [validStep],
+      totalDurationMinutes: 5,
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects missing name', () => {
+    const result = CreateRoutineSchema.safeParse({
+      id: 'routine_001',
+      steps: [validStep],
+      totalDurationMinutes: 5,
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects empty steps array', () => {
+    const result = CreateRoutineSchema.safeParse({
+      ...validMinimal,
+      steps: [],
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects step with invalid transition', () => {
+    const result = CreateRoutineSchema.safeParse({
+      ...validMinimal,
+      steps: [{ ...validStep, transition: 'invalid' }],
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects step duration > 480 minutes', () => {
+    const result = CreateRoutineSchema.safeParse({
+      ...validMinimal,
+      steps: [{ ...validStep, durationMinutes: 500 }],
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects step duration < 0.5 minutes', () => {
+    const result = CreateRoutineSchema.safeParse({
+      ...validMinimal,
+      steps: [{ ...validStep, durationMinutes: 0.1 }],
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects > 50 steps', () => {
+    const steps = Array.from({ length: 51 }, (_, i) => ({
+      ...validStep,
+      id: `step_${i}`,
+    }));
+    const result = CreateRoutineSchema.safeParse({ ...validMinimal, steps });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid status', () => {
+    const result = CreateRoutineSchema.safeParse({
+      ...validMinimal,
+      status: 'deleted',
+    });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── UpdateRoutineSchema ──
+
+describe('UpdateRoutineSchema', () => {
+  it('accepts status update with syncVersion', () => {
+    const result = UpdateRoutineSchema.safeParse({ status: 'paused', syncVersion: 2 });
+    expect(result.success).toBe(true);
+  });
+
+  it('accepts step updates', () => {
+    const result = UpdateRoutineSchema.safeParse({
+      steps: [
+        {
+          id: 's1',
+          label: 'Step 1',
+          durationMinutes: 5,
+          transition: 'immediate',
+          status: 'completed',
+        },
+        {
+          id: 's2',
+          label: 'Step 2',
+          durationMinutes: 10,
+          transition: '1m_break',
+          status: 'active',
+        },
+      ],
+      currentStepIndex: 1,
+      syncVersion: 3,
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('requires syncVersion', () => {
+    const result = UpdateRoutineSchema.safeParse({ status: 'active' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects syncVersion < 1', () => {
+    const result = UpdateRoutineSchema.safeParse({ status: 'active', syncVersion: 0 });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid status', () => {
+    const result = UpdateRoutineSchema.safeParse({ status: 'deleted', syncVersion: 2 });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── RoutineQuerySchema ──
+
+describe('RoutineQuerySchema', () => {
+  it('provides defaults for empty query', () => {
+    const result = RoutineQuerySchema.safeParse({});
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.sortBy).toBe('createdAt');
+      expect(result.data.sortOrder).toBe('desc');
+      expect(result.data.limit).toBe(50);
+      expect(result.data.offset).toBe(0);
+    }
+  });
+
+  it('accepts all filter combinations', () => {
+    const result = RoutineQuerySchema.safeParse({
+      status: 'template',
+      isTemplate: 'true',
+      category: 'health',
+      sortBy: 'name',
+      sortOrder: 'asc',
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.isTemplate).toBe(true);
+    }
+  });
+
+  it('coerces string numbers', () => {
+    const result = RoutineQuerySchema.safeParse({ limit: '25', offset: '5' });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.limit).toBe(25);
+      expect(result.data.offset).toBe(5);
+    }
+  });
+
+  it('rejects limit > 100', () => {
+    const result = RoutineQuerySchema.safeParse({ limit: 200 });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid sortBy', () => {
+    const result = RoutineQuerySchema.safeParse({ sortBy: 'random' });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── RoutineSyncQuerySchema ──
+
+describe('RoutineSyncQuerySchema', () => {
+  it('accepts valid since timestamp', () => {
+    const result = RoutineSyncQuerySchema.safeParse({ since: '2026-03-01T00:00:00.000Z' });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.limit).toBe(100);
+    }
+  });
+
+  it('rejects missing since', () => {
+    const result = RoutineSyncQuerySchema.safeParse({});
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid since format', () => {
+    const result = RoutineSyncQuerySchema.safeParse({ since: 'yesterday' });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── BatchUpsertRoutinesSchema ──
+
+describe('BatchUpsertRoutinesSchema', () => {
+  const validRoutine = {
+    id: 'routine_batch_1',
+    name: 'Batch Routine',
+    steps: [{ id: 's1', label: 'Step', durationMinutes: 5, transition: 'immediate' }],
+    totalDurationMinutes: 5,
+  };
+
+  it('accepts array of valid routines', () => {
+    const result = BatchUpsertRoutinesSchema.safeParse({
+      routines: [validRoutine, { ...validRoutine, id: 'routine_batch_2', name: 'Second' }],
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.routines).toHaveLength(2);
+    }
+  });
+
+  it('rejects empty routines array', () => {
+    const result = BatchUpsertRoutinesSchema.safeParse({ routines: [] });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects missing routines field', () => {
+    const result = BatchUpsertRoutinesSchema.safeParse({});
+    expect(result.success).toBe(false);
+  });
+
+  it('validates each routine in the array', () => {
+    const result = BatchUpsertRoutinesSchema.safeParse({
+      routines: [validRoutine, { id: 'bad' }],
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects > 50 routines', () => {
+    const routines = Array.from({ length: 51 }, (_, i) => ({
+      ...validRoutine,
+      id: `routine_${i}`,
+    }));
+    const result = BatchUpsertRoutinesSchema.safeParse({ routines });
+    expect(result.success).toBe(false);
+  });
+});
--- a/backend/src/modules/routines/types.ts
+++ b/backend/src/modules/routines/types.ts
@ -0,0 +1,154 @@
+/**
+ * Routine types — ChronoMind cross-platform cloud sync.
+ *
+ * Cosmos container: `routines` (partition key: `/userId`)
+ * Product ID: "chronomind"
+ */
+
+import { z } from 'zod';
+
+// ── Enums / constants ──
+
+export const TRANSITION_TYPES = ['immediate', '1m_break', '5m_break', 'custom'] as const;
+export type TransitionType = (typeof TRANSITION_TYPES)[number];
+
+export const ROUTINE_STATUSES = [
+  'template',
+  'ready',
+  'active',
+  'paused',
+  'completed',
+  'cancelled',
+] as const;
+export type RoutineStatus = (typeof ROUTINE_STATUSES)[number];
+
+export const STEP_STATUSES = ['pending', 'active', 'skipped', 'completed'] as const;
+export type StepStatus = (typeof STEP_STATUSES)[number];
+
+// ── Sub-document interfaces ──
+
+export interface RoutineStep {
+  id: string;
+  label: string;
+  durationMinutes: number;
+  transition: TransitionType;
+  customTransitionMinutes?: number;
+  notes?: string;
+  status: StepStatus;
+  startedAt?: string;
+  completedAt?: string;
+}
+
+// ── Main document ──
+
+export interface RoutineDoc {
+  id: string;
+  userId: string;
+  productId: string;
+
+  name: string;
+  description?: string;
+  steps: RoutineStep[];
+  totalDurationMinutes: number;
+  status: RoutineStatus;
+  currentStepIndex: number;
+  isTemplate: boolean;
+  category?: string;
+
+  createdAt: string;
+  startedAt?: string;
+  pausedAt?: string;
+  completedAt?: string;
+  elapsedBeforePause: number;
+
+  // Sync metadata
+  deviceId?: string;
+  lastSyncedAt?: string;
+  syncVersion: number;
+
+  _ts?: number;
+  _etag?: string;
+}
+
+// ── Zod schemas ──
+
+const RoutineStepSchema = z.object({
+  id: z.string().min(1).max(128),
+  label: z.string().min(1).max(500),
+  durationMinutes: z.number().min(0.5).max(480),
+  transition: z.enum(TRANSITION_TYPES),
+  customTransitionMinutes: z.number().min(0).max(60).optional(),
+  notes: z.string().max(2000).optional(),
+  status: z.enum(STEP_STATUSES).default('pending'),
+  startedAt: z.string().datetime().optional(),
+  completedAt: z.string().datetime().optional(),
+});
+
+export const CreateRoutineSchema = z.object({
+  id: z.string().min(1).max(128),
+  name: z.string().min(1).max(500),
+  description: z.string().max(2000).optional(),
+  steps: z.array(RoutineStepSchema).min(1).max(50),
+  totalDurationMinutes: z.number().min(0),
+  status: z.enum(ROUTINE_STATUSES).default('ready'),
+  currentStepIndex: z.number().int().min(0).default(0),
+  isTemplate: z.boolean().default(false),
+  category: z.string().max(128).optional(),
+  elapsedBeforePause: z.number().min(0).default(0),
+  startedAt: z.string().datetime().optional(),
+  deviceId: z.string().max(256).optional(),
+  syncVersion: z.number().int().min(0).default(1),
+});
+
+export const UpdateRoutineSchema = z.object({
+  name: z.string().min(1).max(500).optional(),
+  description: z.string().max(2000).optional(),
+  steps: z.array(RoutineStepSchema).min(1).max(50).optional(),
+  totalDurationMinutes: z.number().min(0).optional(),
+  status: z.enum(ROUTINE_STATUSES).optional(),
+  currentStepIndex: z.number().int().min(0).optional(),
+  isTemplate: z.boolean().optional(),
+  category: z.string().max(128).optional(),
+  startedAt: z.string().datetime().optional(),
+  pausedAt: z.string().datetime().optional(),
+  completedAt: z.string().datetime().optional(),
+  elapsedBeforePause: z.number().min(0).optional(),
+  deviceId: z.string().max(256).optional(),
+  syncVersion: z.number().int().min(1),
+});
+
+export const RoutineQuerySchema = z.object({
+  status: z.enum(ROUTINE_STATUSES).optional(),
+  isTemplate: z
+    .string()
+    .transform(v => v === 'true')
+    .optional(),
+  category: z.string().optional(),
+  sortBy: z.enum(['createdAt', 'name', 'totalDurationMinutes']).default('createdAt'),
+  sortOrder: z.enum(['asc', 'desc']).default('desc'),
+  limit: z.coerce.number().int().min(1).max(100).default(50),
+  offset: z.coerce.number().int().min(0).default(0),
+});
+
+export const RoutineSyncQuerySchema = z.object({
+  since: z.string().datetime(),
+  limit: z.coerce.number().int().min(1).max(500).default(100),
+});
+
+export const BatchUpsertRoutinesSchema = z.object({
+  routines: z.array(CreateRoutineSchema).min(1).max(50),
+});
+
+// ── Inferred types ──
+
+export type CreateRoutineInput = z.infer<typeof CreateRoutineSchema>;
+export type UpdateRoutineInput = z.infer<typeof UpdateRoutineSchema>;
+export type RoutineQuery = z.infer<typeof RoutineQuerySchema>;
+export type RoutineSyncQuery = z.infer<typeof RoutineSyncQuerySchema>;
+export type BatchUpsertRoutinesInput = z.infer<typeof BatchUpsertRoutinesSchema>;
+
+export interface BatchUpsertRoutinesResult {
+  synced: string[];
+  conflicts: Array<{ id: string; serverVersion: number }>;
+  errors: Array<{ id: string; error: string }>;
+}
--- a/backend/src/modules/shared-timers/repository.ts
+++ b/backend/src/modules/shared-timers/repository.ts
@ -0,0 +1,91 @@
+/**
+ * Shared timers repository — Cosmos DB CRUD for household shared timers.
+ *
+ * Container: shared_timers (partition key: /householdId)
+ */
+
+import { getContainer } from '../../lib/cosmos.js';
+import type { SharedTimerDoc, SharedTimerQuery } from './types.js';
+
+function container() {
+  return getContainer('shared_timers');
+}
+
+export async function listSharedTimers(
+  householdId: string,
+  productId: string,
+  query: SharedTimerQuery
+): Promise<{ items: SharedTimerDoc[]; total: number }> {
+  const conditions: string[] = ['c.householdId = @householdId', 'c.productId = @productId'];
+  const params: { name: string; value: string | number }[] = [
+    { name: '@householdId', value: householdId },
+    { name: '@productId', value: productId },
+  ];
+
+  if (query.state) {
+    conditions.push('c.state = @state');
+    params.push({ name: '@state', value: query.state });
+  }
+  if (query.type) {
+    conditions.push('c.type = @type');
+    params.push({ name: '@type', value: query.type });
+  }
+
+  const where = `WHERE ${conditions.join(' AND ')}`;
+  const sortField = `c.${query.sortBy}`;
+  const orderDir = query.sortOrder.toUpperCase();
+
+  const countResult = await container()
+    .items.query<number>({
+      query: `SELECT VALUE COUNT(1) FROM c ${where}`,
+      parameters: params,
+    })
+    .fetchAll();
+  const total = countResult.resources[0] ?? 0;
+
+  const { resources } = await container()
+    .items.query<SharedTimerDoc>({
+      query: `SELECT * FROM c ${where} ORDER BY ${sortField} ${orderDir} OFFSET @offset LIMIT @limit`,
+      parameters: [
+        ...params,
+        { name: '@offset', value: query.offset },
+        { name: '@limit', value: query.limit },
+      ],
+    })
+    .fetchAll();
+
+  return { items: resources, total };
+}
+
+export async function getSharedTimer(
+  id: string,
+  householdId: string
+): Promise<SharedTimerDoc | null> {
+  try {
+    const { resource } = await container().item(id, householdId).read<SharedTimerDoc>();
+    return resource ?? null;
+  } catch {
+    return null;
+  }
+}
+
+export async function createSharedTimer(doc: SharedTimerDoc): Promise<SharedTimerDoc> {
+  const { resource } = await container().items.create(doc);
+  return resource as SharedTimerDoc;
+}
+
+export async function replaceSharedTimer(doc: SharedTimerDoc): Promise<SharedTimerDoc> {
+  const { resource } = await container().item(doc.id, doc.householdId).replace(doc);
+  return resource as SharedTimerDoc;
+}
+
+export async function deleteSharedTimer(id: string, householdId: string): Promise<boolean> {
+  try {
+    const existing = await getSharedTimer(id, householdId);
+    if (!existing) return false;
+    await container().item(id, householdId).delete();
+    return true;
+  } catch {
+    return false;
+  }
+}
--- a/backend/src/modules/shared-timers/routes.ts
+++ b/backend/src/modules/shared-timers/routes.ts
@ -0,0 +1,183 @@
+/**
+ * Shared timer REST endpoints — ChronoMind Family tier.
+ *
+ * All endpoints require the caller to be a member of the household.
+ *
+ * GET    /households/:householdId/timers           — list shared timers
+ * GET    /households/:householdId/timers/:id       — single shared timer
+ * POST   /households/:householdId/timers           — create shared timer
+ * PUT    /households/:householdId/timers/:id       — update shared timer (creator only)
+ * DELETE /households/:householdId/timers/:id       — delete shared timer (creator or admin)
+ * POST   /households/:householdId/timers/:id/ack   — acknowledge (dismiss/snooze) a timer
+ */
+
+import crypto from 'node:crypto';
+import type { FastifyInstance } from 'fastify';
+import { BadRequestError, NotFoundError, ForbiddenError } from '../../lib/errors.js';
+import { extractAuth } from '../../lib/auth.js';
+import { getHousehold } from '../households/repository.js';
+import * as repo from './repository.js';
+import {
+  CreateSharedTimerSchema,
+  UpdateSharedTimerSchema,
+  AcknowledgeTimerSchema,
+  SharedTimerQuerySchema,
+  type SharedTimerDoc,
+} from './types.js';
+
+const PRODUCT_ID = 'chronomind';
+
+async function requireMembership(householdId: string, userId: string) {
+  const household = await getHousehold(householdId);
+  if (!household || household.productId !== PRODUCT_ID) {
+    throw new NotFoundError('Household not found');
+  }
+  const member = household.members.find(m => m.userId === userId);
+  if (!member) throw new ForbiddenError('Not a member of this household');
+  return { household, member };
+}
+
+export async function sharedTimerRoutes(app: FastifyInstance) {
+  // List shared timers for a household
+  app.get('/households/:householdId/timers', async req => {
+    const auth = await extractAuth(req);
+    const { householdId } = req.params as { householdId: string };
+    await requireMembership(householdId, auth.sub);
+
+    const parsed = SharedTimerQuerySchema.safeParse(req.query);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+    const { items, total } = await repo.listSharedTimers(householdId, PRODUCT_ID, parsed.data);
+    return { items, total, limit: parsed.data.limit, offset: parsed.data.offset };
+  });
+
+  // Get single shared timer
+  app.get('/households/:householdId/timers/:id', async req => {
+    const auth = await extractAuth(req);
+    const { householdId, id } = req.params as { householdId: string; id: string };
+    await requireMembership(householdId, auth.sub);
+
+    const timer = await repo.getSharedTimer(id, householdId);
+    if (!timer) throw new NotFoundError('Shared timer not found');
+    return timer;
+  });
+
+  // Create shared timer
+  app.post('/households/:householdId/timers', async (req, reply) => {
+    const auth = await extractAuth(req);
+    const { householdId } = req.params as { householdId: string };
+    await requireMembership(householdId, auth.sub);
+
+    const parsed = CreateSharedTimerSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    if (parsed.data.householdId !== householdId) {
+      throw new BadRequestError('householdId in body must match URL param');
+    }
+
+    const now = new Date().toISOString();
+    const doc: SharedTimerDoc = {
+      id: crypto.randomUUID(),
+      householdId,
+      productId: PRODUCT_ID,
+      createdBy: auth.sub,
+      label: parsed.data.label,
+      description: parsed.data.description,
+      type: parsed.data.type,
+      state: 'active',
+      urgency: parsed.data.urgency,
+      duration: parsed.data.duration,
+      targetTime: parsed.data.targetTime,
+      category: parsed.data.category,
+      cascade: parsed.data.cascade,
+      acknowledgements: [],
+      createdAt: now,
+      updatedAt: now,
+    };
+
+    req.log.info({ sharedTimerId: doc.id, householdId }, 'Creating shared timer');
+    const created = await repo.createSharedTimer(doc);
+    reply.code(201);
+    return created;
+  });
+
+  // Update shared timer (creator only)
+  app.put('/households/:householdId/timers/:id', async req => {
+    const auth = await extractAuth(req);
+    const { householdId, id } = req.params as { householdId: string; id: string };
+    await requireMembership(householdId, auth.sub);
+
+    const timer = await repo.getSharedTimer(id, householdId);
+    if (!timer) throw new NotFoundError('Shared timer not found');
+    if (timer.createdBy !== auth.sub)
+      throw new ForbiddenError('Only the creator can update this timer');
+
+    const parsed = UpdateSharedTimerSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const now = new Date().toISOString();
+    const updated: SharedTimerDoc = { ...timer, ...parsed.data, updatedAt: now };
+    const result = await repo.replaceSharedTimer(updated);
+    req.log.info({ sharedTimerId: id, householdId }, 'Updated shared timer');
+    return result;
+  });
+
+  // Delete shared timer (creator or admin)
+  app.delete('/households/:householdId/timers/:id', async req => {
+    const auth = await extractAuth(req);
+    const { householdId, id } = req.params as { householdId: string; id: string };
+    const { household } = await requireMembership(householdId, auth.sub);
+
+    const timer = await repo.getSharedTimer(id, householdId);
+    if (!timer) throw new NotFoundError('Shared timer not found');
+
+    const isCreator = timer.createdBy === auth.sub;
+    const isAdmin = household.members.some(m => m.userId === auth.sub && m.role === 'admin');
+    if (!isCreator && !isAdmin) {
+      throw new ForbiddenError('Only the creator or admin can delete this timer');
+    }
+
+    await repo.deleteSharedTimer(id, householdId);
+    req.log.info({ sharedTimerId: id, householdId }, 'Deleted shared timer');
+    return { success: true };
+  });
+
+  // Acknowledge (dismiss/snooze) a shared timer — per-user
+  app.post('/households/:householdId/timers/:id/ack', async req => {
+    const auth = await extractAuth(req);
+    const { householdId, id } = req.params as { householdId: string; id: string };
+    await requireMembership(householdId, auth.sub);
+
+    const timer = await repo.getSharedTimer(id, householdId);
+    if (!timer) throw new NotFoundError('Shared timer not found');
+
+    const parsed = AcknowledgeTimerSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    // Replace or add acknowledgement for this user
+    const now = new Date().toISOString();
+    const existingIdx = timer.acknowledgements.findIndex(a => a.userId === auth.sub);
+    const ack = { userId: auth.sub, state: parsed.data.state, at: now };
+
+    if (existingIdx >= 0) {
+      timer.acknowledgements[existingIdx] = ack;
+    } else {
+      timer.acknowledgements.push(ack);
+    }
+    timer.updatedAt = now;
+
+    const result = await repo.replaceSharedTimer(timer);
+    req.log.info(
+      { sharedTimerId: id, householdId, ackState: parsed.data.state },
+      'Timer acknowledged'
+    );
+    return result;
+  });
+}
--- a/backend/src/modules/shared-timers/shared-timers.test.ts
+++ b/backend/src/modules/shared-timers/shared-timers.test.ts
@ -0,0 +1,249 @@
+/**
+ * Shared timers module unit tests — validates schemas, constants, and types.
+ */
+
+import { describe, it, expect } from 'vitest';
+import {
+  CreateSharedTimerSchema,
+  UpdateSharedTimerSchema,
+  AcknowledgeTimerSchema,
+  SharedTimerQuerySchema,
+  TIMER_TYPES,
+  TIMER_STATES,
+  URGENCY_LEVELS,
+  CASCADE_PRESETS,
+} from './types.js';
+
+// ── Constants ──
+
+describe('shared timer constants', () => {
+  it('has 3 timer types', () => {
+    expect(TIMER_TYPES).toEqual(['countdown', 'alarm', 'pomodoro']);
+  });
+
+  it('has 7 timer states', () => {
+    expect(TIMER_STATES).toHaveLength(7);
+  });
+
+  it('has 5 urgency levels', () => {
+    expect(URGENCY_LEVELS).toHaveLength(5);
+  });
+
+  it('has 4 cascade presets', () => {
+    expect(CASCADE_PRESETS).toEqual(['minimal', 'standard', 'aggressive', 'custom']);
+  });
+});
+
+// ── CreateSharedTimerSchema ──
+
+describe('CreateSharedTimerSchema', () => {
+  const validMinimal = {
+    householdId: 'household_001',
+    label: 'Dinner ready',
+    type: 'countdown',
+    duration: 1800,
+  };
+
+  it('accepts minimal valid input', () => {
+    const result = CreateSharedTimerSchema.safeParse(validMinimal);
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.urgency).toBe('standard');
+      expect(result.data.label).toBe('Dinner ready');
+    }
+  });
+
+  it('accepts full input with cascade', () => {
+    const result = CreateSharedTimerSchema.safeParse({
+      ...validMinimal,
+      description: 'Let everyone know dinner is ready',
+      urgency: 'important',
+      targetTime: '2026-03-01T18:00:00.000Z',
+      category: 'cooking',
+      cascade: { preset: 'standard', intervals: [15, 5, 1] },
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.cascade?.intervals).toEqual([15, 5, 1]);
+    }
+  });
+
+  it('accepts alarm type with targetTime', () => {
+    const result = CreateSharedTimerSchema.safeParse({
+      ...validMinimal,
+      type: 'alarm',
+      targetTime: '2026-03-01T07:00:00.000Z',
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('rejects missing householdId', () => {
+    const result = CreateSharedTimerSchema.safeParse({
+      label: 'Test',
+      type: 'countdown',
+      duration: 300,
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects missing label', () => {
+    const result = CreateSharedTimerSchema.safeParse({
+      householdId: 'h1',
+      type: 'countdown',
+      duration: 300,
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid type', () => {
+    const result = CreateSharedTimerSchema.safeParse({
+      ...validMinimal,
+      type: 'stopwatch',
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid urgency', () => {
+    const result = CreateSharedTimerSchema.safeParse({
+      ...validMinimal,
+      urgency: 'extreme',
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects negative duration', () => {
+    const result = CreateSharedTimerSchema.safeParse({
+      ...validMinimal,
+      duration: -10,
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid targetTime', () => {
+    const result = CreateSharedTimerSchema.safeParse({
+      ...validMinimal,
+      targetTime: 'not-a-date',
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects label > 500 chars', () => {
+    const result = CreateSharedTimerSchema.safeParse({
+      ...validMinimal,
+      label: 'x'.repeat(501),
+    });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── UpdateSharedTimerSchema ──
+
+describe('UpdateSharedTimerSchema', () => {
+  it('accepts state update', () => {
+    const result = UpdateSharedTimerSchema.safeParse({ state: 'fired' });
+    expect(result.success).toBe(true);
+  });
+
+  it('accepts label and urgency update', () => {
+    const result = UpdateSharedTimerSchema.safeParse({
+      label: 'New label',
+      urgency: 'critical',
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('accepts cascade update', () => {
+    const result = UpdateSharedTimerSchema.safeParse({
+      cascade: { preset: 'aggressive', intervals: [30, 10, 5] },
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('accepts empty update', () => {
+    const result = UpdateSharedTimerSchema.safeParse({});
+    expect(result.success).toBe(true);
+  });
+
+  it('rejects invalid state', () => {
+    const result = UpdateSharedTimerSchema.safeParse({ state: 'deleted' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid urgency', () => {
+    const result = UpdateSharedTimerSchema.safeParse({ urgency: 'extreme' });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── AcknowledgeTimerSchema ──
+
+describe('AcknowledgeTimerSchema', () => {
+  it('accepts dismissed', () => {
+    const result = AcknowledgeTimerSchema.safeParse({ state: 'dismissed' });
+    expect(result.success).toBe(true);
+  });
+
+  it('accepts snoozed', () => {
+    const result = AcknowledgeTimerSchema.safeParse({ state: 'snoozed' });
+    expect(result.success).toBe(true);
+  });
+
+  it('rejects other states', () => {
+    const result = AcknowledgeTimerSchema.safeParse({ state: 'active' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects missing state', () => {
+    const result = AcknowledgeTimerSchema.safeParse({});
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── SharedTimerQuerySchema ──
+
+describe('SharedTimerQuerySchema', () => {
+  it('provides defaults for empty query', () => {
+    const result = SharedTimerQuerySchema.safeParse({});
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.sortBy).toBe('createdAt');
+      expect(result.data.sortOrder).toBe('desc');
+      expect(result.data.limit).toBe(50);
+      expect(result.data.offset).toBe(0);
+    }
+  });
+
+  it('accepts state and type filters', () => {
+    const result = SharedTimerQuerySchema.safeParse({
+      state: 'active',
+      type: 'countdown',
+      sortBy: 'targetTime',
+      sortOrder: 'asc',
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('coerces string numbers', () => {
+    const result = SharedTimerQuerySchema.safeParse({ limit: '25', offset: '10' });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.limit).toBe(25);
+      expect(result.data.offset).toBe(10);
+    }
+  });
+
+  it('rejects limit > 100', () => {
+    const result = SharedTimerQuerySchema.safeParse({ limit: 200 });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid sortBy', () => {
+    const result = SharedTimerQuerySchema.safeParse({ sortBy: 'random' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid state filter', () => {
+    const result = SharedTimerQuerySchema.safeParse({ state: 'deleted' });
+    expect(result.success).toBe(false);
+  });
+});
--- a/backend/src/modules/shared-timers/types.ts
+++ b/backend/src/modules/shared-timers/types.ts
@ -0,0 +1,118 @@
+/**
+ * Shared timer types — ChronoMind Family tier.
+ *
+ * Cosmos container: `shared_timers` (partition key: `/householdId`)
+ * Product ID: "chronomind"
+ *
+ * Shared timers are visible to all household members. The creator
+ * owns the timer; any member can snooze/dismiss their own view.
+ */
+
+import { z } from 'zod';
+
+// ── Reuse timer enums ──
+
+export const TIMER_TYPES = ['countdown', 'alarm', 'pomodoro'] as const;
+export const TIMER_STATES = [
+  'active',
+  'paused',
+  'fired',
+  'snoozed',
+  'dismissed',
+  'completed',
+  'warning',
+] as const;
+export const URGENCY_LEVELS = ['critical', 'important', 'standard', 'gentle', 'passive'] as const;
+export const CASCADE_PRESETS = ['minimal', 'standard', 'aggressive', 'custom'] as const;
+
+// ── Sub-document interfaces ──
+
+export interface SharedCascadeConfig {
+  preset: (typeof CASCADE_PRESETS)[number];
+  intervals?: number[];
+}
+
+export interface SharedTimerAck {
+  userId: string;
+  state: 'dismissed' | 'snoozed';
+  at: string;
+}
+
+// ── Main document ──
+
+export interface SharedTimerDoc {
+  id: string;
+  householdId: string;
+  productId: string;
+  createdBy: string;
+
+  label: string;
+  description?: string;
+  type: (typeof TIMER_TYPES)[number];
+  state: (typeof TIMER_STATES)[number];
+  urgency: (typeof URGENCY_LEVELS)[number];
+  duration: number;
+  targetTime?: string;
+  category?: string;
+
+  cascade?: SharedCascadeConfig;
+  acknowledgements: SharedTimerAck[];
+
+  createdAt: string;
+  updatedAt: string;
+  completedAt?: string;
+
+  _ts?: number;
+  _etag?: string;
+}
+
+// ── Zod schemas ──
+
+const CascadeSchema = z.object({
+  preset: z.enum(CASCADE_PRESETS),
+  intervals: z.array(z.number().min(0).max(120)).max(20).optional(),
+});
+
+export const CreateSharedTimerSchema = z.object({
+  householdId: z.string().min(1).max(128),
+  label: z.string().min(1).max(500),
+  description: z.string().max(2000).optional(),
+  type: z.enum(TIMER_TYPES),
+  urgency: z.enum(URGENCY_LEVELS).default('standard'),
+  duration: z.number().min(0),
+  targetTime: z.string().datetime().optional(),
+  category: z.string().max(128).optional(),
+  cascade: CascadeSchema.optional(),
+});
+
+export const UpdateSharedTimerSchema = z.object({
+  label: z.string().min(1).max(500).optional(),
+  description: z.string().max(2000).optional(),
+  state: z.enum(TIMER_STATES).optional(),
+  urgency: z.enum(URGENCY_LEVELS).optional(),
+  duration: z.number().min(0).optional(),
+  targetTime: z.string().datetime().optional(),
+  category: z.string().max(128).optional(),
+  cascade: CascadeSchema.optional(),
+  completedAt: z.string().datetime().optional(),
+});
+
+export const AcknowledgeTimerSchema = z.object({
+  state: z.enum(['dismissed', 'snoozed'] as const),
+});
+
+export const SharedTimerQuerySchema = z.object({
+  state: z.enum(TIMER_STATES).optional(),
+  type: z.enum(TIMER_TYPES).optional(),
+  sortBy: z.enum(['createdAt', 'targetTime', 'updatedAt']).default('createdAt'),
+  sortOrder: z.enum(['asc', 'desc']).default('desc'),
+  limit: z.coerce.number().int().min(1).max(100).default(50),
+  offset: z.coerce.number().int().min(0).default(0),
+});
+
+// ── Inferred types ──
+
+export type CreateSharedTimerInput = z.infer<typeof CreateSharedTimerSchema>;
+export type UpdateSharedTimerInput = z.infer<typeof UpdateSharedTimerSchema>;
+export type AcknowledgeTimerInput = z.infer<typeof AcknowledgeTimerSchema>;
+export type SharedTimerQuery = z.infer<typeof SharedTimerQuerySchema>;
--- a/backend/src/modules/timers/repository.ts
+++ b/backend/src/modules/timers/repository.ts
@ -0,0 +1,191 @@
+/**
+ * Timers repository — Cosmos DB CRUD + sync + batch upsert.
+ *
+ * Container: timers (partition key: /userId)
+ */
+
+import { getContainer } from '../../lib/cosmos.js';
+import type { TimerDoc, TimerQuery, BatchUpsertResult } from './types.js';
+
+function container() {
+  return getContainer('timers');
+}
+
+export async function listTimers(
+  userId: string,
+  productId: string,
+  query: TimerQuery
+): Promise<{ items: TimerDoc[]; total: number }> {
+  const conditions: string[] = ['c.userId = @userId', 'c.productId = @productId'];
+  const params: { name: string; value: string | number }[] = [
+    { name: '@userId', value: userId },
+    { name: '@productId', value: productId },
+  ];
+
+  if (query.state) {
+    conditions.push('c.state = @state');
+    params.push({ name: '@state', value: query.state });
+  }
+  if (query.type) {
+    conditions.push('c.type = @type');
+    params.push({ name: '@type', value: query.type });
+  }
+  if (query.urgency) {
+    conditions.push('c.urgency = @urgency');
+    params.push({ name: '@urgency', value: query.urgency });
+  }
+  if (query.category) {
+    conditions.push('c.category = @category');
+    params.push({ name: '@category', value: query.category });
+  }
+
+  const where = `WHERE ${conditions.join(' AND ')}`;
+  const sortField = `c.${query.sortBy}`;
+  const orderDir = query.sortOrder.toUpperCase();
+
+  // Count query
+  const countResult = await container()
+    .items.query<number>({
+      query: `SELECT VALUE COUNT(1) FROM c ${where}`,
+      parameters: params,
+    })
+    .fetchAll();
+  const total = countResult.resources[0] ?? 0;
+
+  // Data query with pagination
+  const { resources } = await container()
+    .items.query<TimerDoc>({
+      query: `SELECT * FROM c ${where} ORDER BY ${sortField} ${orderDir} OFFSET @offset LIMIT @limit`,
+      parameters: [
+        ...params,
+        { name: '@offset', value: query.offset },
+        { name: '@limit', value: query.limit },
+      ],
+    })
+    .fetchAll();
+
+  return { items: resources, total };
+}
+
+export async function getTimer(id: string, userId: string): Promise<TimerDoc | null> {
+  try {
+    const { resource } = await container().item(id, userId).read<TimerDoc>();
+    return resource ?? null;
+  } catch {
+    return null;
+  }
+}
+
+export async function createTimer(doc: TimerDoc): Promise<TimerDoc> {
+  const { resource } = await container().items.create(doc);
+  return resource as TimerDoc;
+}
+
+export async function updateTimer(
+  id: string,
+  userId: string,
+  updates: Partial<TimerDoc>,
+  expectedSyncVersion: number
+): Promise<{ doc: TimerDoc | null; conflict: boolean; serverVersion?: number }> {
+  try {
+    const { resource: existing } = await container().item(id, userId).read<TimerDoc>();
+    if (!existing) return { doc: null, conflict: false };
+
+    // Optimistic concurrency: reject stale writes
+    if (expectedSyncVersion <= existing.syncVersion) {
+      return { doc: null, conflict: true, serverVersion: existing.syncVersion };
+    }
+
+    const now = new Date().toISOString();
+    const merged: TimerDoc = {
+      ...existing,
+      ...updates,
+      syncVersion: expectedSyncVersion,
+      lastSyncedAt: now,
+    };
+    const { resource } = await container().item(id, userId).replace(merged);
+    return { doc: resource as TimerDoc, conflict: false };
+  } catch {
+    return { doc: null, conflict: false };
+  }
+}
+
+export async function deleteTimer(id: string, userId: string): Promise<boolean> {
+  try {
+    const { resource: existing } = await container().item(id, userId).read<TimerDoc>();
+    if (!existing) return false;
+    await container().item(id, userId).delete();
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export async function getTimersSince(
+  userId: string,
+  productId: string,
+  sinceTimestamp: string,
+  limit: number
+): Promise<TimerDoc[]> {
+  const { resources } = await container()
+    .items.query<TimerDoc>({
+      query:
+        'SELECT * FROM c WHERE c.userId = @userId AND c.productId = @productId AND c.lastSyncedAt >= @since ORDER BY c.lastSyncedAt ASC OFFSET 0 LIMIT @limit',
+      parameters: [
+        { name: '@userId', value: userId },
+        { name: '@productId', value: productId },
+        { name: '@since', value: sinceTimestamp },
+        { name: '@limit', value: limit },
+      ],
+    })
+    .fetchAll();
+  return resources;
+}
+
+export async function batchUpsert(
+  userId: string,
+  productId: string,
+  timers: Array<Record<string, unknown> & { id: string; syncVersion: number }>
+): Promise<BatchUpsertResult> {
+  const synced: string[] = [];
+  const conflicts: Array<{ id: string; serverVersion: number }> = [];
+  const errors: Array<{ id: string; error: string }> = [];
+
+  for (const timer of timers) {
+    try {
+      const existing = await getTimer(timer.id, userId);
+      const now = new Date().toISOString();
+
+      if (existing) {
+        // Upsert: accept if incoming syncVersion >= existing
+        if (timer.syncVersion >= existing.syncVersion) {
+          const merged: TimerDoc = {
+            ...existing,
+            ...timer,
+            userId,
+            productId,
+            lastSyncedAt: now,
+          };
+          await container().item(timer.id, userId).replace(merged);
+          synced.push(timer.id);
+        } else {
+          conflicts.push({ id: timer.id, serverVersion: existing.syncVersion });
+        }
+      } else {
+        // New document
+        const doc: TimerDoc = {
+          ...timer,
+          userId,
+          productId,
+          lastSyncedAt: now,
+        } as TimerDoc;
+        await container().items.create(doc);
+        synced.push(timer.id);
+      }
+    } catch (err) {
+      errors.push({ id: timer.id, error: err instanceof Error ? err.message : 'Unknown error' });
+    }
+  }
+
+  return { synced, conflicts, errors };
+}
--- a/backend/src/modules/timers/routes.ts
+++ b/backend/src/modules/timers/routes.ts
@ -0,0 +1,158 @@
+/**
+ * Timer REST endpoints — ChronoMind cloud sync.
+ *
+ * GET    /timers           — list user's timers (filterable, paginated)
+ * GET    /timers/sync      — delta sync (timers modified since timestamp)
+ * GET    /timers/:id       — single timer
+ * POST   /timers           — create timer
+ * PUT    /timers/:id       — update timer (with syncVersion conflict check)
+ * DELETE /timers/:id       — delete timer
+ * POST   /timers/batch     — batch upsert (offline queue flush / initial sync)
+ */
+
+import type { FastifyInstance } from 'fastify';
+import { BadRequestError, NotFoundError, ConflictError } from '../../lib/errors.js';
+import { extractAuth } from '../../lib/auth.js';
+import * as repo from './repository.js';
+import {
+  CreateTimerSchema,
+  UpdateTimerSchema,
+  TimerQuerySchema,
+  TimerSyncQuerySchema,
+  BatchUpsertSchema,
+  type TimerDoc,
+} from './types.js';
+
+const PRODUCT_ID = 'chronomind';
+
+export async function timerRoutes(app: FastifyInstance) {
+  // Sync — must be before :id param route
+  app.get('/timers/sync', async req => {
+    const auth = await extractAuth(req);
+    const parsed = TimerSyncQuerySchema.safeParse(req.query);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+    const timers = await repo.getTimersSince(
+      auth.sub,
+      PRODUCT_ID,
+      parsed.data.since,
+      parsed.data.limit
+    );
+    return { timers, count: timers.length };
+  });
+
+  // List timers
+  app.get('/timers', async req => {
+    const auth = await extractAuth(req);
+    const parsed = TimerQuerySchema.safeParse(req.query);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+    const { items, total } = await repo.listTimers(auth.sub, PRODUCT_ID, parsed.data);
+    return { items, total, limit: parsed.data.limit, offset: parsed.data.offset };
+  });
+
+  // Get single timer
+  app.get('/timers/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    const timer = await repo.getTimer(id, auth.sub);
+    if (!timer) throw new NotFoundError('Timer not found');
+    if (timer.productId !== PRODUCT_ID) throw new NotFoundError('Timer not found');
+    return timer;
+  });
+
+  // Create timer
+  app.post('/timers', async (req, reply) => {
+    const auth = await extractAuth(req);
+    const parsed = CreateTimerSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+    const input = parsed.data;
+    const now = new Date().toISOString();
+
+    const doc: TimerDoc = {
+      id: input.id,
+      userId: auth.sub,
+      productId: PRODUCT_ID,
+      label: input.label,
+      description: input.description,
+      type: input.type,
+      state: input.state,
+      urgency: input.urgency,
+      duration: input.duration,
+      targetTime: input.targetTime,
+      createdAt: now,
+      startedAt: input.startedAt,
+      cascade: input.cascade,
+      pomodoro: input.pomodoro,
+      isCalendarSync: input.isCalendarSync,
+      calendarEventId: input.calendarEventId,
+      category: input.category,
+      deviceId: input.deviceId,
+      lastSyncedAt: now,
+      syncVersion: input.syncVersion,
+    };
+
+    req.log.info({ timerId: doc.id, type: doc.type }, 'Creating timer');
+    const created = await repo.createTimer(doc);
+    reply.code(201);
+    return created;
+  });
+
+  // Update timer (with syncVersion conflict check)
+  app.put('/timers/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+
+    const parsed = UpdateTimerSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const { syncVersion, ...updates } = parsed.data;
+    const result = await repo.updateTimer(id, auth.sub, updates, syncVersion);
+
+    if (result.conflict) {
+      throw new ConflictError(
+        `Sync conflict: server version is ${result.serverVersion}, received ${syncVersion}`
+      );
+    }
+    if (!result.doc) throw new NotFoundError('Timer not found');
+
+    req.log.info({ timerId: id, syncVersion }, 'Updated timer');
+    return result.doc;
+  });
+
+  // Delete timer
+  app.delete('/timers/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    const success = await repo.deleteTimer(id, auth.sub);
+    if (!success) throw new NotFoundError('Timer not found');
+    req.log.info({ timerId: id }, 'Deleted timer');
+    return { success: true };
+  });
+
+  // Batch upsert (initial sync / offline queue flush)
+  app.post('/timers/batch', async req => {
+    const auth = await extractAuth(req);
+    const parsed = BatchUpsertSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+
+    const now = new Date().toISOString();
+    const enriched = parsed.data.timers.map(t => ({
+      ...t,
+      createdAt: now,
+      lastSyncedAt: now,
+    }));
+
+    req.log.info({ count: enriched.length }, 'Batch upsert timers');
+    const result = await repo.batchUpsert(auth.sub, PRODUCT_ID, enriched);
+    return result;
+  });
+}
--- a/backend/src/modules/timers/timers.test.ts
+++ b/backend/src/modules/timers/timers.test.ts
@ -0,0 +1,408 @@
+/**
+ * Timers module unit tests — validates schemas, constants, and type guards.
+ */
+
+import { describe, it, expect } from 'vitest';
+import {
+  CreateTimerSchema,
+  UpdateTimerSchema,
+  TimerQuerySchema,
+  TimerSyncQuerySchema,
+  BatchUpsertSchema,
+  TIMER_TYPES,
+  TIMER_STATES,
+  URGENCY_LEVELS,
+  CASCADE_PRESETS,
+} from './types.js';
+
+// ── Constants ──
+
+describe('type constants', () => {
+  it('has 3 timer types', () => {
+    expect(TIMER_TYPES).toEqual(['countdown', 'alarm', 'pomodoro']);
+  });
+
+  it('has 7 timer states', () => {
+    expect(TIMER_STATES).toEqual([
+      'active',
+      'paused',
+      'fired',
+      'snoozed',
+      'dismissed',
+      'completed',
+      'warning',
+    ]);
+    expect(TIMER_STATES).toHaveLength(7);
+  });
+
+  it('has 5 urgency levels', () => {
+    expect(URGENCY_LEVELS).toEqual(['critical', 'important', 'standard', 'gentle', 'passive']);
+    expect(URGENCY_LEVELS).toHaveLength(5);
+  });
+
+  it('has 4 cascade presets', () => {
+    expect(CASCADE_PRESETS).toEqual(['minimal', 'standard', 'aggressive', 'custom']);
+  });
+});
+
+// ── CreateTimerSchema ──
+
+describe('CreateTimerSchema', () => {
+  const validMinimal = {
+    id: 'timer_001',
+    label: 'Morning alarm',
+    type: 'alarm',
+    duration: 0,
+    targetTime: '2026-03-01T07:00:00.000Z',
+  };
+
+  it('accepts minimal valid input with defaults', () => {
+    const result = CreateTimerSchema.safeParse(validMinimal);
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.id).toBe('timer_001');
+      expect(result.data.label).toBe('Morning alarm');
+      expect(result.data.type).toBe('alarm');
+      expect(result.data.state).toBe('active');
+      expect(result.data.urgency).toBe('standard');
+      expect(result.data.syncVersion).toBe(1);
+    }
+  });
+
+  it('accepts full countdown timer with cascade', () => {
+    const result = CreateTimerSchema.safeParse({
+      ...validMinimal,
+      type: 'countdown',
+      state: 'active',
+      urgency: 'critical',
+      duration: 300,
+      description: 'Important meeting prep',
+      cascade: {
+        preset: 'aggressive',
+        intervals: [30, 15, 5, 1],
+      },
+      deviceId: 'iphone-14-pro',
+      category: 'work',
+      syncVersion: 3,
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.cascade?.preset).toBe('aggressive');
+      expect(result.data.cascade?.intervals).toEqual([30, 15, 5, 1]);
+      expect(result.data.urgency).toBe('critical');
+      expect(result.data.syncVersion).toBe(3);
+    }
+  });
+
+  it('accepts pomodoro timer with full config', () => {
+    const result = CreateTimerSchema.safeParse({
+      ...validMinimal,
+      type: 'pomodoro',
+      pomodoro: {
+        focusMinutes: 25,
+        shortBreakMinutes: 5,
+        longBreakMinutes: 15,
+        roundsBeforeLong: 4,
+        currentRound: 1,
+        isBreak: false,
+        totalRoundsCompleted: 0,
+      },
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.pomodoro?.focusMinutes).toBe(25);
+      expect(result.data.pomodoro?.roundsBeforeLong).toBe(4);
+    }
+  });
+
+  it('accepts timer with calendar sync', () => {
+    const result = CreateTimerSchema.safeParse({
+      ...validMinimal,
+      isCalendarSync: true,
+      calendarEventId: 'cal_abc123',
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('rejects missing id', () => {
+    const result = CreateTimerSchema.safeParse({
+      label: 'Morning alarm',
+      type: 'alarm',
+      duration: 0,
+      targetTime: '2026-03-01T07:00:00.000Z',
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects missing label', () => {
+    const result = CreateTimerSchema.safeParse({
+      id: 'timer_001',
+      type: 'alarm',
+      duration: 0,
+      targetTime: '2026-03-01T07:00:00.000Z',
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects missing type', () => {
+    const result = CreateTimerSchema.safeParse({
+      id: 'timer_001',
+      label: 'Morning alarm',
+      duration: 0,
+      targetTime: '2026-03-01T07:00:00.000Z',
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid type', () => {
+    const result = CreateTimerSchema.safeParse({ ...validMinimal, type: 'stopwatch' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid state', () => {
+    const result = CreateTimerSchema.safeParse({ ...validMinimal, state: 'deleted' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid urgency', () => {
+    const result = CreateTimerSchema.safeParse({ ...validMinimal, urgency: 'extreme' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid targetTime format', () => {
+    const result = CreateTimerSchema.safeParse({ ...validMinimal, targetTime: 'not-a-date' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects negative duration', () => {
+    const result = CreateTimerSchema.safeParse({ ...validMinimal, duration: -10 });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects label > 500 chars', () => {
+    const result = CreateTimerSchema.safeParse({ ...validMinimal, label: 'x'.repeat(501) });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects pomodoro focusMinutes > 120', () => {
+    const result = CreateTimerSchema.safeParse({
+      ...validMinimal,
+      pomodoro: {
+        focusMinutes: 150,
+        shortBreakMinutes: 5,
+        longBreakMinutes: 15,
+        roundsBeforeLong: 4,
+        currentRound: 0,
+        isBreak: false,
+        totalRoundsCompleted: 0,
+      },
+    });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── UpdateTimerSchema ──
+
+describe('UpdateTimerSchema', () => {
+  it('accepts state update with syncVersion', () => {
+    const result = UpdateTimerSchema.safeParse({ state: 'paused', syncVersion: 2 });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.state).toBe('paused');
+      expect(result.data.syncVersion).toBe(2);
+    }
+  });
+
+  it('accepts complete update with timestamps', () => {
+    const result = UpdateTimerSchema.safeParse({
+      state: 'completed',
+      completedAt: '2026-03-01T08:00:00.000Z',
+      syncVersion: 5,
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('accepts pomodoro round update', () => {
+    const result = UpdateTimerSchema.safeParse({
+      pomodoro: {
+        focusMinutes: 25,
+        shortBreakMinutes: 5,
+        longBreakMinutes: 15,
+        roundsBeforeLong: 4,
+        currentRound: 3,
+        isBreak: true,
+        totalRoundsCompleted: 2,
+      },
+      syncVersion: 4,
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('requires syncVersion', () => {
+    const result = UpdateTimerSchema.safeParse({ state: 'paused' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects syncVersion < 1', () => {
+    const result = UpdateTimerSchema.safeParse({ state: 'paused', syncVersion: 0 });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid state', () => {
+    const result = UpdateTimerSchema.safeParse({ state: 'deleted', syncVersion: 2 });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid completedAt format', () => {
+    const result = UpdateTimerSchema.safeParse({
+      completedAt: 'yesterday',
+      syncVersion: 2,
+    });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── TimerQuerySchema ──
+
+describe('TimerQuerySchema', () => {
+  it('provides defaults for empty query', () => {
+    const result = TimerQuerySchema.safeParse({});
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.sortBy).toBe('createdAt');
+      expect(result.data.sortOrder).toBe('desc');
+      expect(result.data.limit).toBe(50);
+      expect(result.data.offset).toBe(0);
+    }
+  });
+
+  it('coerces string numbers for limit and offset', () => {
+    const result = TimerQuerySchema.safeParse({ limit: '25', offset: '10' });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.limit).toBe(25);
+      expect(result.data.offset).toBe(10);
+    }
+  });
+
+  it('accepts all filter combinations', () => {
+    const result = TimerQuerySchema.safeParse({
+      state: 'active',
+      type: 'pomodoro',
+      urgency: 'critical',
+      category: 'work',
+      sortBy: 'targetTime',
+      sortOrder: 'asc',
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('rejects limit > 100', () => {
+    const result = TimerQuerySchema.safeParse({ limit: 200 });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects negative offset', () => {
+    const result = TimerQuerySchema.safeParse({ offset: -1 });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid sortBy', () => {
+    const result = TimerQuerySchema.safeParse({ sortBy: 'random' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid state filter', () => {
+    const result = TimerQuerySchema.safeParse({ state: 'deleted' });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── TimerSyncQuerySchema ──
+
+describe('TimerSyncQuerySchema', () => {
+  it('accepts valid since timestamp', () => {
+    const result = TimerSyncQuerySchema.safeParse({ since: '2026-03-01T00:00:00.000Z' });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.limit).toBe(100);
+    }
+  });
+
+  it('accepts custom limit', () => {
+    const result = TimerSyncQuerySchema.safeParse({
+      since: '2026-03-01T00:00:00.000Z',
+      limit: '50',
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.limit).toBe(50);
+    }
+  });
+
+  it('rejects missing since', () => {
+    const result = TimerSyncQuerySchema.safeParse({});
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects invalid since format', () => {
+    const result = TimerSyncQuerySchema.safeParse({ since: 'yesterday' });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects limit > 500', () => {
+    const result = TimerSyncQuerySchema.safeParse({
+      since: '2026-03-01T00:00:00.000Z',
+      limit: 1000,
+    });
+    expect(result.success).toBe(false);
+  });
+});
+
+// ── BatchUpsertSchema ──
+
+describe('BatchUpsertSchema', () => {
+  const validTimer = {
+    id: 'timer_batch_1',
+    label: 'Batch timer',
+    type: 'countdown',
+    duration: 600,
+    targetTime: '2026-03-01T10:00:00.000Z',
+  };
+
+  it('accepts array of valid timers', () => {
+    const result = BatchUpsertSchema.safeParse({
+      timers: [validTimer, { ...validTimer, id: 'timer_batch_2', label: 'Second timer' }],
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.timers).toHaveLength(2);
+    }
+  });
+
+  it('rejects empty timers array', () => {
+    const result = BatchUpsertSchema.safeParse({ timers: [] });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects missing timers field', () => {
+    const result = BatchUpsertSchema.safeParse({});
+    expect(result.success).toBe(false);
+  });
+
+  it('validates each timer in the array', () => {
+    const result = BatchUpsertSchema.safeParse({
+      timers: [validTimer, { id: 'bad', type: 'invalid' }],
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('rejects > 100 timers', () => {
+    const timers = Array.from({ length: 101 }, (_, i) => ({
+      ...validTimer,
+      id: `timer_${i}`,
+    }));
+    const result = BatchUpsertSchema.safeParse({ timers });
+    expect(result.success).toBe(false);
+  });
+});
--- a/backend/src/modules/timers/types.ts
+++ b/backend/src/modules/timers/types.ts
@ -0,0 +1,175 @@
+/**
+ * Timer types — ChronoMind cross-platform cloud sync.
+ *
+ * Cosmos container: `timers` (partition key: `/userId`)
+ * Product ID: "chronomind"
+ */
+
+import { z } from 'zod';
+
+// ── Enums / constants ──
+
+export const TIMER_TYPES = ['countdown', 'alarm', 'pomodoro'] as const;
+export type TimerType = (typeof TIMER_TYPES)[number];
+
+export const TIMER_STATES = [
+  'active',
+  'paused',
+  'fired',
+  'snoozed',
+  'dismissed',
+  'completed',
+  'warning',
+] as const;
+export type TimerState = (typeof TIMER_STATES)[number];
+
+export const URGENCY_LEVELS = ['critical', 'important', 'standard', 'gentle', 'passive'] as const;
+export type UrgencyLevel = (typeof URGENCY_LEVELS)[number];
+
+export const CASCADE_PRESETS = ['minimal', 'standard', 'aggressive', 'custom'] as const;
+export type CascadePreset = (typeof CASCADE_PRESETS)[number];
+
+// ── Sub-document interfaces ──
+
+export interface CascadeConfig {
+  preset: CascadePreset;
+  intervals: number[];
+}
+
+export interface PomodoroConfig {
+  focusMinutes: number;
+  shortBreakMinutes: number;
+  longBreakMinutes: number;
+  roundsBeforeLong: number;
+  currentRound: number;
+  isBreak: boolean;
+  totalRoundsCompleted: number;
+}
+
+// ── Main document ──
+
+export interface TimerDoc {
+  id: string;
+  userId: string;
+  productId: string;
+
+  label: string;
+  description?: string;
+  type: TimerType;
+  state: TimerState;
+  urgency: UrgencyLevel;
+
+  duration: number;
+  targetTime: string;
+  createdAt: string;
+  startedAt?: string;
+  pausedAt?: string;
+  firedAt?: string;
+  completedAt?: string;
+
+  cascade?: CascadeConfig;
+  pomodoro?: PomodoroConfig;
+
+  isCalendarSync?: boolean;
+  calendarEventId?: string;
+  category?: string;
+
+  deviceId?: string;
+  lastSyncedAt?: string;
+  syncVersion: number;
+
+  _ts?: number;
+  _etag?: string;
+}
+
+// ── Zod schemas ──
+
+const CascadeSchema = z.object({
+  preset: z.enum(CASCADE_PRESETS),
+  intervals: z.array(z.number().int().min(0)),
+});
+
+const PomodoroSchema = z.object({
+  focusMinutes: z.number().int().min(1).max(120),
+  shortBreakMinutes: z.number().int().min(1).max(60),
+  longBreakMinutes: z.number().int().min(1).max(120),
+  roundsBeforeLong: z.number().int().min(1).max(20),
+  currentRound: z.number().int().min(0),
+  isBreak: z.boolean(),
+  totalRoundsCompleted: z.number().int().min(0),
+});
+
+export const CreateTimerSchema = z.object({
+  id: z.string().min(1).max(128),
+  label: z.string().min(1).max(500),
+  description: z.string().max(2000).optional(),
+  type: z.enum(TIMER_TYPES),
+  state: z.enum(TIMER_STATES).default('active'),
+  urgency: z.enum(URGENCY_LEVELS).default('standard'),
+  duration: z.number().int().min(0),
+  targetTime: z.string().datetime(),
+  cascade: CascadeSchema.optional(),
+  pomodoro: PomodoroSchema.optional(),
+  isCalendarSync: z.boolean().optional(),
+  calendarEventId: z.string().max(500).optional(),
+  category: z.string().max(128).optional(),
+  deviceId: z.string().max(256).optional(),
+  startedAt: z.string().datetime().optional(),
+  syncVersion: z.number().int().min(0).default(1),
+});
+
+export const UpdateTimerSchema = z.object({
+  label: z.string().min(1).max(500).optional(),
+  description: z.string().max(2000).optional(),
+  state: z.enum(TIMER_STATES).optional(),
+  urgency: z.enum(URGENCY_LEVELS).optional(),
+  duration: z.number().int().min(0).optional(),
+  targetTime: z.string().datetime().optional(),
+  startedAt: z.string().datetime().optional(),
+  pausedAt: z.string().datetime().optional(),
+  firedAt: z.string().datetime().optional(),
+  completedAt: z.string().datetime().optional(),
+  cascade: CascadeSchema.optional(),
+  pomodoro: PomodoroSchema.optional(),
+  isCalendarSync: z.boolean().optional(),
+  calendarEventId: z.string().max(500).optional(),
+  category: z.string().max(128).optional(),
+  deviceId: z.string().max(256).optional(),
+  syncVersion: z.number().int().min(1),
+});
+
+export const TimerQuerySchema = z.object({
+  state: z.enum(TIMER_STATES).optional(),
+  type: z.enum(TIMER_TYPES).optional(),
+  urgency: z.enum(URGENCY_LEVELS).optional(),
+  category: z.string().optional(),
+  sortBy: z.enum(['createdAt', 'targetTime', 'label']).default('createdAt'),
+  sortOrder: z.enum(['asc', 'desc']).default('desc'),
+  limit: z.coerce.number().int().min(1).max(100).default(50),
+  offset: z.coerce.number().int().min(0).default(0),
+});
+
+export const TimerSyncQuerySchema = z.object({
+  since: z.string().datetime(),
+  limit: z.coerce.number().int().min(1).max(500).default(100),
+});
+
+export const BatchUpsertSchema = z.object({
+  timers: z.array(CreateTimerSchema).min(1).max(100),
+});
+
+// ── Inferred types ──
+
+export type CreateTimerInput = z.infer<typeof CreateTimerSchema>;
+export type UpdateTimerInput = z.infer<typeof UpdateTimerSchema>;
+export type TimerQuery = z.infer<typeof TimerQuerySchema>;
+export type TimerSyncQuery = z.infer<typeof TimerSyncQuerySchema>;
+export type BatchUpsertInput = z.infer<typeof BatchUpsertSchema>;
+
+// ── Batch result ──
+
+export interface BatchUpsertResult {
+  synced: string[];
+  conflicts: Array<{ id: string; serverVersion: number }>;
+  errors: Array<{ id: string; error: string }>;
+}
--- a/backend/src/modules/webhooks/dispatcher.ts
+++ b/backend/src/modules/webhooks/dispatcher.ts
@ -0,0 +1,200 @@
+import { createHmac } from 'node:crypto';
+import type { WebhookEventType, WebhookSubscriptionDoc, WebhookEventDoc } from './types.js';
+import * as repo from './repository.js';
+
+// ── HMAC Signing ──────────────────────────────────────────────
+
+export function signPayload(payload: string, secret: string): string {
+  return createHmac('sha256', secret).update(payload).digest('hex');
+}
+
+export function buildSignatureHeader(payload: string, secret: string): string {
+  const timestamp = Math.floor(Date.now() / 1000);
+  const signature = createHmac('sha256', secret).update(`${timestamp}.${payload}`).digest('hex');
+  return `t=${timestamp},v1=${signature}`;
+}
+
+// ── Delivery ──────────────────────────────────────────────────
+
+export interface DeliveryResult {
+  subscriptionId: string;
+  eventId: string;
+  success: boolean;
+  statusCode?: number;
+  error?: string;
+}
+
+/**
+ * Dispatch a webhook event to all matching subscriptions for a user.
+ * Returns delivery results for each subscription.
+ */
+export async function dispatchEvent(
+  userId: string,
+  productId: string,
+  eventType: WebhookEventType,
+  payload: Record<string, unknown>,
+  log?: { info: (...args: unknown[]) => void; error: (...args: unknown[]) => void }
+): Promise<DeliveryResult[]> {
+  const subscriptions = await repo.findSubscriptionsForEvent(userId, productId, eventType);
+
+  if (subscriptions.length === 0) {
+    return [];
+  }
+
+  const results: DeliveryResult[] = [];
+
+  for (const sub of subscriptions) {
+    const result = await deliverToSubscription(sub, eventType, payload, log);
+    results.push(result);
+  }
+
+  return results;
+}
+
+/**
+ * Deliver a single event to a single subscription.
+ * Creates an event log entry and handles retries.
+ */
+async function deliverToSubscription(
+  sub: WebhookSubscriptionDoc,
+  eventType: WebhookEventType,
+  payload: Record<string, unknown>,
+  log?: { info: (...args: unknown[]) => void; error: (...args: unknown[]) => void }
+): Promise<DeliveryResult> {
+  const eventId = crypto.randomUUID();
+  const now = new Date().toISOString();
+
+  // Create event log entry
+  const eventDoc: WebhookEventDoc = {
+    id: eventId,
+    subscriptionId: sub.id,
+    userId: sub.userId,
+    productId: sub.productId,
+    eventType,
+    payload,
+    createdAt: now,
+    attempts: 0,
+    maxRetries: sub.maxRetries,
+  };
+
+  await repo.createEvent(eventDoc);
+
+  // Attempt delivery with retries
+  const maxAttempts = (sub.maxRetries || 3) + 1;
+  let lastError: string | undefined;
+  let statusCode: number | undefined;
+
+  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
+    try {
+      const bodyJson = JSON.stringify({
+        id: eventId,
+        type: eventType,
+        timestamp: now,
+        data: payload,
+      });
+
+      const signatureHeader = buildSignatureHeader(bodyJson, sub.secret);
+
+      const controller = new globalThis.AbortController();
+      const timeout = globalThis.setTimeout(() => controller.abort(), 10_000);
+
+      const response = await fetch(sub.url, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          'X-Webhook-Signature': signatureHeader,
+          'X-Webhook-Id': eventId,
+          'X-Webhook-Event': eventType,
+          'User-Agent': 'ChronoMind-Webhooks/1.0',
+        },
+        body: bodyJson,
+        signal: controller.signal,
+      });
+
+      globalThis.clearTimeout(timeout);
+      statusCode = response.status;
+
+      if (response.ok) {
+        // Success — update event log
+        await repo.updateEvent({
+          ...eventDoc,
+          deliveredAt: new Date().toISOString(),
+          statusCode,
+          attempts: attempt,
+        });
+        await repo.resetFailureCount(sub.id, sub.userId);
+
+        log?.info({ subscriptionId: sub.id, eventType, attempt, statusCode }, 'webhook delivered');
+
+        return {
+          subscriptionId: sub.id,
+          eventId,
+          success: true,
+          statusCode,
+        };
+      }
+
+      lastError = `HTTP ${statusCode}`;
+    } catch (err: unknown) {
+      lastError = err instanceof Error ? err.message : String(err);
+    }
+
+    // Exponential backoff between retries (100ms, 200ms, 400ms, ...)
+    if (attempt < maxAttempts) {
+      const delay = Math.min(100 * Math.pow(2, attempt - 1), 5000);
+      await new Promise<void>(resolve => globalThis.setTimeout(resolve, delay));
+    }
+  }
+
+  // All attempts failed
+  await repo.updateEvent({
+    ...eventDoc,
+    attempts: maxAttempts,
+    error: lastError,
+    statusCode,
+  });
+  await repo.incrementFailureCount(sub.id, sub.userId);
+
+  log?.error({ subscriptionId: sub.id, eventType, error: lastError }, 'webhook delivery failed');
+
+  return {
+    subscriptionId: sub.id,
+    eventId,
+    success: false,
+    statusCode,
+    error: lastError,
+  };
+}
+
+// ── Verify Signature (for consumers) ──────────────────────────
+
+export function verifySignature(
+  signatureHeader: string,
+  body: string,
+  secret: string,
+  toleranceSeconds = 300
+): boolean {
+  const parts = signatureHeader.split(',');
+  const timestampPart = parts.find(p => p.startsWith('t='));
+  const signaturePart = parts.find(p => p.startsWith('v1='));
+
+  if (!timestampPart || !signaturePart) return false;
+
+  const timestamp = parseInt(timestampPart.slice(2), 10);
+  const signature = signaturePart.slice(3);
+
+  // Check timestamp tolerance
+  const now = Math.floor(Date.now() / 1000);
+  if (Math.abs(now - timestamp) > toleranceSeconds) return false;
+
+  // Verify HMAC
+  const expected = createHmac('sha256', secret).update(`${timestamp}.${body}`).digest('hex');
+
+  // Constant-time comparison
+  if (expected.length !== signature.length) return false;
+  let diff = 0;
+  for (let i = 0; i < expected.length; i++) {
+    diff |= expected.charCodeAt(i) ^ signature.charCodeAt(i);
+  }
+  return diff === 0;
+}
--- a/backend/src/modules/webhooks/repository.ts
+++ b/backend/src/modules/webhooks/repository.ts
@ -0,0 +1,192 @@
+import { getContainer } from '../../lib/cosmos.js';
+import { NotFoundError, ConflictError } from '../../lib/errors.js';
+import type {
+  WebhookSubscriptionDoc,
+  WebhookEventDoc,
+  CreateSubscription,
+  UpdateSubscription,
+  WebhookEventType,
+} from './types.js';
+
+const SUBS_CONTAINER = 'webhook_subscriptions';
+const EVENTS_CONTAINER = 'webhook_events';
+
+function subsContainer() {
+  return getContainer(SUBS_CONTAINER);
+}
+
+function eventsContainer() {
+  return getContainer(EVENTS_CONTAINER);
+}
+
+// ── Subscription CRUD ─────────────────────────────────────────
+
+export async function listSubscriptions(
+  userId: string,
+  productId: string
+): Promise<WebhookSubscriptionDoc[]> {
+  const { resources } = await subsContainer()
+    .items.query<WebhookSubscriptionDoc>(
+      {
+        query:
+          'SELECT * FROM c WHERE c.userId = @userId AND c.productId = @productId ORDER BY c.createdAt DESC',
+        parameters: [
+          { name: '@userId', value: userId },
+          { name: '@productId', value: productId },
+        ],
+      },
+      { partitionKey: userId }
+    )
+    .fetchAll();
+
+  return resources;
+}
+
+export async function getSubscription(id: string, userId: string): Promise<WebhookSubscriptionDoc> {
+  const { resource } = await subsContainer().item(id, userId).read<WebhookSubscriptionDoc>();
+  if (!resource) {
+    throw new NotFoundError(`Webhook subscription '${id}' not found`);
+  }
+  return resource;
+}
+
+export async function createSubscription(
+  id: string,
+  userId: string,
+  productId: string,
+  input: CreateSubscription
+): Promise<WebhookSubscriptionDoc> {
+  const now = new Date().toISOString();
+  const doc: WebhookSubscriptionDoc = {
+    id,
+    userId,
+    productId,
+    url: input.url,
+    secret: input.secret,
+    events: input.events,
+    active: true,
+    description: input.description,
+    createdAt: now,
+    updatedAt: now,
+    failureCount: 0,
+    maxRetries: input.maxRetries ?? 3,
+  };
+
+  try {
+    const { resource } = await subsContainer().items.create(doc);
+    return resource as WebhookSubscriptionDoc;
+  } catch (err: unknown) {
+    if (err && typeof err === 'object' && 'code' in err && err.code === 409) {
+      throw new ConflictError(`Subscription '${id}' already exists`);
+    }
+    throw err;
+  }
+}
+
+export async function updateSubscription(
+  id: string,
+  userId: string,
+  updates: UpdateSubscription
+): Promise<WebhookSubscriptionDoc> {
+  const existing = await getSubscription(id, userId);
+
+  const updated: WebhookSubscriptionDoc = {
+    ...existing,
+    ...updates,
+    updatedAt: new Date().toISOString(),
+  };
+
+  const { resource } = await subsContainer().item(id, userId).replace(updated);
+  return resource as WebhookSubscriptionDoc;
+}
+
+export async function deleteSubscription(id: string, userId: string): Promise<void> {
+  await getSubscription(id, userId); // verify exists
+  await subsContainer().item(id, userId).delete();
+}
+
+// ── Find Subscriptions for Event ──────────────────────────────
+
+export async function findSubscriptionsForEvent(
+  userId: string,
+  productId: string,
+  eventType: WebhookEventType
+): Promise<WebhookSubscriptionDoc[]> {
+  const { resources } = await subsContainer()
+    .items.query<WebhookSubscriptionDoc>(
+      {
+        query:
+          'SELECT * FROM c WHERE c.userId = @userId AND c.productId = @productId AND c.active = true AND ARRAY_CONTAINS(c.events, @eventType)',
+        parameters: [
+          { name: '@userId', value: userId },
+          { name: '@productId', value: productId },
+          { name: '@eventType', value: eventType },
+        ],
+      },
+      { partitionKey: userId }
+    )
+    .fetchAll();
+
+  return resources;
+}
+
+// ── Increment Failure Count ───────────────────────────────────
+
+export async function incrementFailureCount(id: string, userId: string): Promise<void> {
+  const existing = await getSubscription(id, userId);
+  const failureCount = (existing.failureCount || 0) + 1;
+
+  // Auto-disable after 10 consecutive failures
+  const active = failureCount < 10;
+
+  await subsContainer()
+    .item(id, userId)
+    .replace({
+      ...existing,
+      failureCount,
+      active,
+      updatedAt: new Date().toISOString(),
+    });
+}
+
+export async function resetFailureCount(id: string, userId: string): Promise<void> {
+  const existing = await getSubscription(id, userId);
+  await subsContainer()
+    .item(id, userId)
+    .replace({
+      ...existing,
+      failureCount: 0,
+      lastDeliveryAt: new Date().toISOString(),
+      updatedAt: new Date().toISOString(),
+    });
+}
+
+// ── Event Log ─────────────────────────────────────────────────
+
+export async function createEvent(doc: WebhookEventDoc): Promise<WebhookEventDoc> {
+  const { resource } = await eventsContainer().items.create(doc);
+  return resource as WebhookEventDoc;
+}
+
+export async function updateEvent(doc: WebhookEventDoc): Promise<WebhookEventDoc> {
+  const { resource } = await eventsContainer().item(doc.id, doc.subscriptionId).replace(doc);
+  return resource as WebhookEventDoc;
+}
+
+export async function listEvents(subscriptionId: string, limit = 50): Promise<WebhookEventDoc[]> {
+  const { resources } = await eventsContainer()
+    .items.query<WebhookEventDoc>(
+      {
+        query:
+          'SELECT TOP @limit * FROM c WHERE c.subscriptionId = @subscriptionId ORDER BY c.createdAt DESC',
+        parameters: [
+          { name: '@subscriptionId', value: subscriptionId },
+          { name: '@limit', value: limit },
+        ],
+      },
+      { partitionKey: subscriptionId }
+    )
+    .fetchAll();
+
+  return resources;
+}
--- a/backend/src/modules/webhooks/routes.ts
+++ b/backend/src/modules/webhooks/routes.ts
@ -0,0 +1,111 @@
+import type { FastifyInstance } from 'fastify';
+
+import {
+  CreateSubscriptionSchema,
+  UpdateSubscriptionSchema,
+  WEBHOOK_EVENT_TYPES,
+} from './types.js';
+import * as repo from './repository.js';
+import { dispatchEvent } from './dispatcher.js';
+import { extractAuth } from '../../lib/auth.js';
+import { BadRequestError } from '../../lib/errors.js';
+
+const PRODUCT_ID = 'chronomind';
+
+export async function webhookRoutes(app: FastifyInstance) {
+  // Event types — must be before :id param route
+  app.get('/webhooks/event-types', async (_req, reply) => {
+    return reply.send({
+      eventTypes: WEBHOOK_EVENT_TYPES.map(type => ({
+        type,
+        category: type.split('.')[0],
+        action: type.split('.')[1],
+      })),
+    });
+  });
+
+  // Test — must be before :id param route
+  app.post('/webhooks/test', async (req, reply) => {
+    const auth = await extractAuth(req);
+    const body = req.body as { subscriptionId?: string; eventType?: string };
+
+    if (!body.subscriptionId) {
+      throw new BadRequestError('subscriptionId is required');
+    }
+
+    await repo.getSubscription(body.subscriptionId, auth.sub);
+
+    const eventType = (body.eventType || 'timer.fired') as (typeof WEBHOOK_EVENT_TYPES)[number];
+    if (!WEBHOOK_EVENT_TYPES.includes(eventType)) {
+      throw new BadRequestError(`Invalid event type: ${eventType}`);
+    }
+
+    const results = await dispatchEvent(
+      auth.sub,
+      PRODUCT_ID,
+      eventType,
+      {
+        test: true,
+        message: 'This is a test webhook event from ChronoMind',
+        timestamp: new Date().toISOString(),
+      },
+      req.log
+    );
+
+    return reply.send({ results });
+  });
+
+  // List subscriptions
+  app.get('/webhooks', async req => {
+    const auth = await extractAuth(req);
+    return repo.listSubscriptions(auth.sub, PRODUCT_ID);
+  });
+
+  // Get subscription
+  app.get('/webhooks/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    return repo.getSubscription(id, auth.sub);
+  });
+
+  // Create subscription
+  app.post('/webhooks', async (req, reply) => {
+    const auth = await extractAuth(req);
+    const parsed = CreateSubscriptionSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+    const id = crypto.randomUUID();
+    const sub = await repo.createSubscription(id, auth.sub, PRODUCT_ID, parsed.data);
+    return reply.status(201).send(sub);
+  });
+
+  // Update subscription
+  app.put('/webhooks/:id', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    const parsed = UpdateSubscriptionSchema.safeParse(req.body);
+    if (!parsed.success) {
+      throw new BadRequestError(parsed.error.issues.map(i => i.message).join('; '));
+    }
+    return repo.updateSubscription(id, auth.sub, parsed.data);
+  });
+
+  // Delete subscription
+  app.delete('/webhooks/:id', async (req, reply) => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    await repo.deleteSubscription(id, auth.sub);
+    return reply.status(204).send();
+  });
+
+  // List events for subscription
+  app.get('/webhooks/:id/events', async req => {
+    const auth = await extractAuth(req);
+    const { id } = req.params as { id: string };
+    // Verify ownership
+    await repo.getSubscription(id, auth.sub);
+    const limit = parseInt((req.query as Record<string, string>).limit || '50', 10);
+    return repo.listEvents(id, Math.min(limit, 100));
+  });
+}
--- a/backend/src/modules/webhooks/types.ts
+++ b/backend/src/modules/webhooks/types.ts
@ -0,0 +1,95 @@
+import { z } from 'zod';
+
+// ── Webhook Event Types ───────────────────────────────────────
+
+export const WEBHOOK_EVENT_TYPES = [
+  'timer.created',
+  'timer.fired',
+  'timer.dismissed',
+  'timer.completed',
+  'timer.snoozed',
+  'timer.paused',
+  'timer.resumed',
+  'routine.started',
+  'routine.completed',
+  'routine.step_completed',
+  'household.member_joined',
+  'household.member_left',
+  'shared_timer.created',
+  'shared_timer.fired',
+  'shared_timer.acknowledged',
+] as const;
+
+export type WebhookEventType = (typeof WEBHOOK_EVENT_TYPES)[number];
+
+// ── Subscription Schemas ──────────────────────────────────────
+
+export const WebhookSubscriptionSchema = z.object({
+  id: z.string().min(1),
+  userId: z.string().min(1),
+  productId: z.string().min(1),
+  url: z.string().url(),
+  secret: z.string().min(16).max(256),
+  events: z.array(z.enum(WEBHOOK_EVENT_TYPES)).min(1),
+  active: z.boolean().default(true),
+  description: z.string().optional(),
+  createdAt: z.string().optional(),
+  updatedAt: z.string().optional(),
+  lastDeliveryAt: z.string().optional(),
+  failureCount: z.number().default(0),
+  maxRetries: z.number().default(3),
+});
+
+export const CreateSubscriptionSchema = z.object({
+  url: z.string().url(),
+  secret: z.string().min(16).max(256),
+  events: z.array(z.enum(WEBHOOK_EVENT_TYPES)).min(1),
+  description: z.string().optional(),
+  maxRetries: z.number().min(0).max(10).optional(),
+});
+
+export const UpdateSubscriptionSchema = z.object({
+  url: z.string().url().optional(),
+  secret: z.string().min(16).max(256).optional(),
+  events: z.array(z.enum(WEBHOOK_EVENT_TYPES)).min(1).optional(),
+  active: z.boolean().optional(),
+  description: z.string().optional(),
+  maxRetries: z.number().min(0).max(10).optional(),
+});
+
+// ── Event Payload Schema ──────────────────────────────────────
+
+export const WebhookEventSchema = z.object({
+  id: z.string().min(1),
+  subscriptionId: z.string().min(1),
+  userId: z.string().min(1),
+  productId: z.string().min(1),
+  eventType: z.enum(WEBHOOK_EVENT_TYPES),
+  payload: z.record(z.unknown()),
+  createdAt: z.string(),
+  deliveredAt: z.string().optional(),
+  statusCode: z.number().optional(),
+  attempts: z.number().default(0),
+  maxRetries: z.number().default(3),
+  nextRetryAt: z.string().optional(),
+  error: z.string().optional(),
+});
+
+// ── TypeScript Types ──────────────────────────────────────────
+
+export type WebhookSubscription = z.infer<typeof WebhookSubscriptionSchema>;
+export type CreateSubscription = z.infer<typeof CreateSubscriptionSchema>;
+export type UpdateSubscription = z.infer<typeof UpdateSubscriptionSchema>;
+export type WebhookEvent = z.infer<typeof WebhookEventSchema>;
+
+// ── Cosmos Document Shapes ────────────────────────────────────
+
+export interface WebhookSubscriptionDoc extends WebhookSubscription {
+  _ts?: number;
+  _etag?: string;
+}
+
+export interface WebhookEventDoc extends WebhookEvent {
+  _ts?: number;
+  _etag?: string;
+}
--- a/backend/src/modules/webhooks/webhooks.test.ts
+++ b/backend/src/modules/webhooks/webhooks.test.ts
@ -0,0 +1,356 @@
+import { describe, it, expect } from 'vitest';
+import {
+  WebhookSubscriptionSchema,
+  CreateSubscriptionSchema,
+  UpdateSubscriptionSchema,
+  WebhookEventSchema,
+  WEBHOOK_EVENT_TYPES,
+  type WebhookSubscription,
+  type CreateSubscription,
+  type WebhookEvent,
+} from './types.js';
+import { signPayload, buildSignatureHeader, verifySignature } from './dispatcher.js';
+
+// ── Types & Schema Tests ──────────────────────────────────────
+
+describe('Webhook Types', () => {
+  it('should define 15 event types', () => {
+    expect(WEBHOOK_EVENT_TYPES).toHaveLength(15);
+  });
+
+  it('should include all timer event types', () => {
+    const timerEvents = WEBHOOK_EVENT_TYPES.filter(e => e.startsWith('timer.'));
+    expect(timerEvents).toEqual([
+      'timer.created',
+      'timer.fired',
+      'timer.dismissed',
+      'timer.completed',
+      'timer.snoozed',
+      'timer.paused',
+      'timer.resumed',
+    ]);
+  });
+
+  it('should include all routine event types', () => {
+    const routineEvents = WEBHOOK_EVENT_TYPES.filter(e => e.startsWith('routine.'));
+    expect(routineEvents).toEqual([
+      'routine.started',
+      'routine.completed',
+      'routine.step_completed',
+    ]);
+  });
+
+  it('should include all household event types', () => {
+    const householdEvents = WEBHOOK_EVENT_TYPES.filter(e => e.startsWith('household.'));
+    expect(householdEvents).toEqual(['household.member_joined', 'household.member_left']);
+  });
+
+  it('should include all shared_timer event types', () => {
+    const sharedEvents = WEBHOOK_EVENT_TYPES.filter(e => e.startsWith('shared_timer.'));
+    expect(sharedEvents).toEqual([
+      'shared_timer.created',
+      'shared_timer.fired',
+      'shared_timer.acknowledged',
+    ]);
+  });
+
+  it('should have unique event types', () => {
+    const unique = new Set(WEBHOOK_EVENT_TYPES);
+    expect(unique.size).toBe(WEBHOOK_EVENT_TYPES.length);
+  });
+});
+
+describe('WebhookSubscriptionSchema', () => {
+  const validSub: WebhookSubscription = {
+    id: 'sub-1',
+    userId: 'user-1',
+    productId: 'chronomind',
+    url: 'https://example.com/webhook',
+    secret: 'super-secret-key-1234567',
+    events: ['timer.fired', 'timer.dismissed'],
+    active: true,
+    failureCount: 0,
+    maxRetries: 3,
+  };
+
+  it('should validate a correct subscription', () => {
+    const result = WebhookSubscriptionSchema.safeParse(validSub);
+    expect(result.success).toBe(true);
+  });
+
+  it('should reject subscription without url', () => {
+    const result = WebhookSubscriptionSchema.safeParse({ ...validSub, url: '' });
+    expect(result.success).toBe(false);
+  });
+
+  it('should reject subscription with invalid url', () => {
+    const result = WebhookSubscriptionSchema.safeParse({ ...validSub, url: 'not-a-url' });
+    expect(result.success).toBe(false);
+  });
+
+  it('should reject subscription with short secret', () => {
+    const result = WebhookSubscriptionSchema.safeParse({ ...validSub, secret: 'short' });
+    expect(result.success).toBe(false);
+  });
+
+  it('should reject subscription with empty events', () => {
+    const result = WebhookSubscriptionSchema.safeParse({ ...validSub, events: [] });
+    expect(result.success).toBe(false);
+  });
+
+  it('should reject subscription with invalid event type', () => {
+    const result = WebhookSubscriptionSchema.safeParse({
+      ...validSub,
+      events: ['timer.fired', 'invalid.event'],
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('should default active to true', () => {
+    const withoutActive = { ...validSub };
+    delete (withoutActive as Record<string, unknown>).active;
+    const result = WebhookSubscriptionSchema.safeParse(withoutActive);
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.active).toBe(true);
+    }
+  });
+
+  it('should default failureCount to 0', () => {
+    const withoutCount = { ...validSub };
+    delete (withoutCount as Record<string, unknown>).failureCount;
+    const result = WebhookSubscriptionSchema.safeParse(withoutCount);
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.failureCount).toBe(0);
+    }
+  });
+});
+
+describe('CreateSubscriptionSchema', () => {
+  const validCreate: CreateSubscription = {
+    url: 'https://hooks.zapier.com/abc123',
+    secret: 'webhook-signing-secret-abc123',
+    events: ['timer.fired'],
+  };
+
+  it('should validate a correct create payload', () => {
+    const result = CreateSubscriptionSchema.safeParse(validCreate);
+    expect(result.success).toBe(true);
+  });
+
+  it('should accept optional description', () => {
+    const result = CreateSubscriptionSchema.safeParse({
+      ...validCreate,
+      description: 'My Zapier integration',
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('should accept optional maxRetries', () => {
+    const result = CreateSubscriptionSchema.safeParse({
+      ...validCreate,
+      maxRetries: 5,
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.maxRetries).toBe(5);
+    }
+  });
+
+  it('should reject maxRetries > 10', () => {
+    const result = CreateSubscriptionSchema.safeParse({
+      ...validCreate,
+      maxRetries: 15,
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it('should accept multiple event types', () => {
+    const result = CreateSubscriptionSchema.safeParse({
+      ...validCreate,
+      events: ['timer.fired', 'timer.dismissed', 'routine.completed'],
+    });
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.events).toHaveLength(3);
+    }
+  });
+});
+
+describe('UpdateSubscriptionSchema', () => {
+  it('should validate partial updates', () => {
+    const result = UpdateSubscriptionSchema.safeParse({ active: false });
+    expect(result.success).toBe(true);
+  });
+
+  it('should validate url-only update', () => {
+    const result = UpdateSubscriptionSchema.safeParse({
+      url: 'https://new-endpoint.example.com/hook',
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('should validate events update', () => {
+    const result = UpdateSubscriptionSchema.safeParse({
+      events: ['timer.created', 'timer.completed'],
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('should reject empty events array in update', () => {
+    const result = UpdateSubscriptionSchema.safeParse({ events: [] });
+    expect(result.success).toBe(false);
+  });
+});
+
+describe('WebhookEventSchema', () => {
+  const validEvent: WebhookEvent = {
+    id: 'evt-1',
+    subscriptionId: 'sub-1',
+    userId: 'user-1',
+    productId: 'chronomind',
+    eventType: 'timer.fired',
+    payload: { timerId: 'timer-1', label: 'Meeting' },
+    createdAt: new Date().toISOString(),
+    attempts: 1,
+    maxRetries: 3,
+  };
+
+  it('should validate a correct event', () => {
+    const result = WebhookEventSchema.safeParse(validEvent);
+    expect(result.success).toBe(true);
+  });
+
+  it('should accept delivered event with statusCode', () => {
+    const result = WebhookEventSchema.safeParse({
+      ...validEvent,
+      deliveredAt: new Date().toISOString(),
+      statusCode: 200,
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it('should accept failed event with error', () => {
+    const result = WebhookEventSchema.safeParse({
+      ...validEvent,
+      error: 'Connection refused',
+      attempts: 4,
+    });
+    expect(result.success).toBe(true);
+  });
+});
+
+// ── Dispatcher Tests ──────────────────────────────────────────
+
+describe('Webhook Dispatcher — HMAC Signing', () => {
+  const secret = 'test-secret-key-for-hmac-1234';
+  const payload = JSON.stringify({ type: 'timer.fired', data: { id: 'timer-1' } });
+
+  it('should produce consistent HMAC signatures', () => {
+    const sig1 = signPayload(payload, secret);
+    const sig2 = signPayload(payload, secret);
+    expect(sig1).toBe(sig2);
+    expect(sig1).toMatch(/^[0-9a-f]{64}$/); // SHA-256 hex
+  });
+
+  it('should produce different signatures for different payloads', () => {
+    const sig1 = signPayload('payload-1', secret);
+    const sig2 = signPayload('payload-2', secret);
+    expect(sig1).not.toBe(sig2);
+  });
+
+  it('should produce different signatures for different secrets', () => {
+    const sig1 = signPayload(payload, 'secret-1-aaaaaaaaaa');
+    const sig2 = signPayload(payload, 'secret-2-bbbbbbbbbb');
+    expect(sig1).not.toBe(sig2);
+  });
+});
+
+describe('Webhook Dispatcher — Signature Header', () => {
+  const secret = 'test-secret-key-for-hmac-5678';
+  const body = '{"type":"timer.fired","data":{}}';
+
+  it('should build a valid signature header', () => {
+    const header = buildSignatureHeader(body, secret);
+    expect(header).toMatch(/^t=\d+,v1=[0-9a-f]{64}$/);
+  });
+
+  it('should include a recent timestamp', () => {
+    const header = buildSignatureHeader(body, secret);
+    const tPart = header.split(',')[0];
+    const timestamp = parseInt(tPart.slice(2), 10);
+    const now = Math.floor(Date.now() / 1000);
+    expect(Math.abs(now - timestamp)).toBeLessThan(5);
+  });
+});
+
+describe('Webhook Dispatcher — Signature Verification', () => {
+  const secret = 'test-secret-for-verification!';
+  const body = JSON.stringify({ type: 'timer.dismissed', data: { id: 't-99' } });
+
+  it('should verify a valid signature', () => {
+    const header = buildSignatureHeader(body, secret);
+    expect(verifySignature(header, body, secret)).toBe(true);
+  });
+
+  it('should reject a tampered body', () => {
+    const header = buildSignatureHeader(body, secret);
+    expect(verifySignature(header, body + 'tampered', secret)).toBe(false);
+  });
+
+  it('should reject a wrong secret', () => {
+    const header = buildSignatureHeader(body, secret);
+    expect(verifySignature(header, body, 'wrong-secret-1234567890')).toBe(false);
+  });
+
+  it('should reject a malformed header', () => {
+    expect(verifySignature('invalid', body, secret)).toBe(false);
+  });
+
+  it('should reject missing timestamp', () => {
+    expect(verifySignature('v1=abc123', body, secret)).toBe(false);
+  });
+
+  it('should reject missing signature', () => {
+    expect(verifySignature('t=1234567890', body, secret)).toBe(false);
+  });
+
+  it('should reject expired timestamp', () => {
+    // Build a header with a timestamp from 10 minutes ago
+    const oldTimestamp = Math.floor(Date.now() / 1000) - 600;
+    // signPayload produces HMAC of the raw string, matching verifySignature's `${timestamp}.${body}` pattern
+    const sig = signPayload(`${oldTimestamp}.${body}`, secret);
+    const header = `t=${oldTimestamp},v1=${sig}`;
+    // Default tolerance is 300 seconds (5 minutes) — 600s ago should be rejected
+    expect(verifySignature(header, body, secret, 300)).toBe(false);
+  });
+
+  it('should accept within tolerance window', () => {
+    const header = buildSignatureHeader(body, secret);
+    // Use a large tolerance window
+    expect(verifySignature(header, body, secret, 3600)).toBe(true);
+  });
+});
+
+// ── Event Type Categorization Tests ───────────────────────────
+
+describe('Event Type Categories', () => {
+  it('all event types should have category.action format', () => {
+    for (const type of WEBHOOK_EVENT_TYPES) {
+      const parts = type.split('.');
+      expect(parts).toHaveLength(2);
+      expect(parts[0].length).toBeGreaterThan(0);
+      expect(parts[1].length).toBeGreaterThan(0);
+    }
+  });
+
+  it('should have 4 categories', () => {
+    const categories = new Set(WEBHOOK_EVENT_TYPES.map(t => t.split('.')[0]));
+    expect(categories.size).toBe(4);
+    expect(categories).toContain('timer');
+    expect(categories).toContain('routine');
+    expect(categories).toContain('household');
+    expect(categories).toContain('shared_timer');
+  });
+});
--- a/backend/src/server.ts
+++ b/backend/src/server.ts
@ -0,0 +1,55 @@
+/**
+ * ChronoMind Backend — Fastify server entry point.
+ *
+ * Product-specific service for timers, routines, households, shared timers.
+ * Common platform features (auth, billing, flags, etc.) come from platform-service.
+ * Port: 4011 (configurable via PORT env var).
+ */
+
+import { createServiceApp, startService } from '@bytelyst/fastify-core';
+import { timerRoutes } from './modules/timers/routes.js';
+import { routineRoutes } from './modules/routines/routes.js';
+import { householdRoutes } from './modules/households/routes.js';
+import { sharedTimerRoutes } from './modules/shared-timers/routes.js';
+import { webhookRoutes } from './modules/webhooks/routes.js';
+import { initCosmosIfNeeded } from './lib/cosmos-init.js';
+import { config } from './lib/config.js';
+
+import { jwtVerify } from 'jose';
+import type { JwtPayload } from './lib/request-context.js';
+
+const jwtSecret = new TextEncoder().encode(process.env.JWT_SECRET || '');
+
+await initCosmosIfNeeded();
+
+const app = await createServiceApp({
+  name: 'chronomind-backend',
+  version: '0.1.0',
+  description: 'ChronoMind product-specific backend — timers, routines, households, shared timers, webhooks',
+  corsOrigin: config.CORS_ORIGIN,
+  swagger: {
+    title: 'ChronoMind Backend',
+    description: 'Timers, routines, households, shared timers, webhooks',
+    port: config.PORT,
+  },
+  metrics: true,
+});
+
+app.addHook('onRequest', async req => {
+  const auth = req.headers.authorization;
+  if (!auth?.startsWith('Bearer ')) return;
+  try {
+    const { payload } = await jwtVerify(auth.slice(7), jwtSecret, { issuer: 'bytelyst-platform' });
+    req.jwtPayload = payload as unknown as JwtPayload;
+  } catch {
+    // Token invalid/expired — leave jwtPayload undefined.
+  }
+});
+
+await app.register(timerRoutes, { prefix: '/api' });
+await app.register(routineRoutes, { prefix: '/api' });
+await app.register(householdRoutes, { prefix: '/api' });
+await app.register(sharedTimerRoutes, { prefix: '/api' });
+await app.register(webhookRoutes, { prefix: '/api' });
+
+await startService(app, { port: config.PORT, host: config.HOST });
--- a/backend/tsconfig.json
+++ b/backend/tsconfig.json
@ -0,0 +1,20 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "lib": ["ES2022"],
+    "outDir": "dist",
+    "rootDir": "src",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "resolveJsonModule": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true
+  },
+  "include": ["src/**/*.ts"],
+  "exclude": ["dist", "node_modules", "src/**/*.test.ts"]
+}
--- a/backend/vitest.config.ts
+++ b/backend/vitest.config.ts
@ -0,0 +1,8 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    globals: true,
+    passWithNoTests: true,
+  },
+});