From 9ed80cd0bc56a011ba9b95f0b0f5dcba5f949088 Mon Sep 17 00:00:00 2001
From: hailin <hailin.zhao@gdzx.xyz>
Date: Tue, 3 Mar 2026 21:09:17 -0800
Subject: [PATCH] feat: implement complete commercial monetization loop (Phases
 1-4)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

## Phase 1 - Token Metering + Quota Enforcement

### Usage Tracking
- agent-service: add UsageRecord entity (per-tenant schema) tracking
  inputTokens/outputTokens/costUsd per AI task
- Modify all 3 AI engines (claude-api, claude-code-cli, claude-agent-sdk)
  to emit separate input/output token counts in the `completed` event
- claude-api-engine: costUsd = (input*3 + output*15) / 1,000,000
  (claude-sonnet-4-5 pricing: $3/MTok in, $15/MTok out)
- agent.controller: persist UsageRecord and publish `usage.recorded`
  event to Redis Streams on every task completion (non-blocking)
- shared/events: new events UsageRecordedEvent, SubscriptionChangedEvent,
  QuotaExceededEvent, PaymentReceivedEvent

### Quota Enforcement
- TenantInfo: add maxServers, maxUsers, maxStandingOrders,
  maxAgentTokensPerMonth fields
- TenantContextMiddleware: rewritten to query public.tenants table for
  real quota values; 5-min in-memory cache; plan-based fallback on error
- TenantContextService: getTenant() returns null instead of throwing;
  added getTenantOrThrow() for strict callers
- inventory-service/server.controller: 429 when maxServers exceeded
- ops-service/standing-order.controller: 429 when maxStandingOrders exceeded
- auth-service/auth.service: 429 when maxUsers exceeded
- 002-create-tenant-schema-template.sql: add usage_records table

## Phase 2 - billing-service (New Microservice, port 3010)

### Domain Layer (public schema, all UUIDs)
Entities: Plan, Subscription, Invoice, InvoiceItem, Payment, PaymentMethod,
UsageAggregate

Domain services:
- SubscriptionLifecycleService: full state machine (trialing -> active ->
  past_due -> cancelled/expired); upgrades immediate, downgrades at period end
- InvoiceGeneratorService: monthly invoice = base fee + overage charges;
  proration item for mid-cycle upgrades
- OverageCalculatorService: (totalTokens - includedTokens) * overageRate

### Infrastructure (all repos use DataSource directly, NOT TenantAwareRepository)
- PlanRepository, SubscriptionRepository, InvoiceRepository (atomic
  transaction for invoice+items), PaymentRepository (payments + methods),
  UsageAggregateRepository (UPSERT via ON CONFLICT for atomic accumulation)

### Application Use Cases
- CreateSubscriptionUseCase: called on tenant registration
- ChangePlanUseCase: upgrade (immediate + proration) or downgrade (scheduled)
- CancelSubscriptionUseCase: immediate or at-period-end
- GenerateMonthlyInvoiceUseCase: cron target (1st of month 00:05 UTC);
  generates invoices, renews periods, applies scheduled downgrades
- AggregateUsageUseCase: Redis Streams consumer group billing-service,
  upserts monthly usage aggregates from usage.recorded events
- CheckTokenQuotaUseCase: hard limit enforcement per plan
- CreatePaymentSessionUseCase + HandlePaymentWebhookUseCase

### REST API
- GET  /api/v1/billing/plans
- GET/POST /api/v1/billing/subscription (+ /upgrade, /cancel)
- GET  /api/v1/billing/invoices (paginated)
- GET  /api/v1/billing/invoices/:id
- POST /api/v1/billing/invoices/:id/pay
- GET  /api/v1/billing/usage/current + /history
- CRUD /api/v1/billing/payment-methods
- POST /api/v1/billing/webhooks/{stripe,alipay,wechat,crypto}

### Plan Seed (auto on startup via PlanSeedService)
- free:       $0/mo,    100K tokens,  no overage,  hard limit 100%
- pro:        $49.99/mo, 1M tokens,  $8/MTok,  hard limit 150%
- enterprise: $199.99/mo, 10M tokens, $5/MTok, no hard limit

## Phase 3 - Payment Provider Integration

### PaymentProviderRegistry (Strategy Pattern, mirrors EngineRegistry)
All providers use @Optional() injection; unconfigured providers omitted

- StripeProvider: PaymentIntent API; webhook via stripe.webhooks.constructEvent
- AlipayProvider: alipay-sdk; Native QR (precreate); RSA2 signature verify
- WeChatPayProvider: v3 REST; Native Pay code_url; AES-256-GCM decrypt;
  HMAC-SHA256 request signing and webhook verification
- CryptoProvider: Coinbase Commerce; hosted checkout; HMAC-SHA256 verify

### WebhookController
All 4 webhook endpoints are public (no JWT) for payment provider callbacks.
rawBody: true enabled in main.ts for signature verification.

## Infrastructure Changes
- docker-compose.yml: billing-service container (port 13010);
  added as dependency of api-gateway
- kong.yml: /api/v1/billing routes (JWT); /api/v1/billing/webhooks (public)
- 005-create-billing-tables.sql: 7 billing tables + invoice sequence +
  ALTER tenants to add quota columns
- run-migrations.ts: 005 runs as part of shared schema step

## Phase 4 - Frontend

### Web Admin (Next.js)
New pages:
- /billing: subscription card + token usage bar + warning banner + invoices
- /billing/plans: comparison grid with USD/CNY toggle + upgrade/downgrade flow
- /billing/invoices: paginated table with Pay Now button
Sidebar: Billing group (CreditCard icon, 3 sub-items)
i18n: billing keys added to en + zh sidebar translations

### Flutter App
New feature module it0_app/lib/features/billing/:
- BillingOverviewPage: plan card + token LinearProgressIndicator +
  latest invoice + upgrade button
- BillingProvider (FutureProvider): parallel fetch subscription/quota/invoice
Settings page: "订阅与用量" entry card
Router: /settings/billing sub-route

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 deploy/docker/docker-compose.yml              |  44 +++
 .../src/app/(admin)/billing/invoices/page.tsx | 146 ++++++++
 .../src/app/(admin)/billing/page.tsx          | 228 +++++++++++++
 .../src/app/(admin)/billing/plans/page.tsx    | 214 ++++++++++++
 .../src/i18n/locales/en/sidebar.json          |   4 +
 .../src/i18n/locales/zh/sidebar.json          |   4 +
 .../components/layout/sidebar.tsx             |  12 +
 it0_app/lib/core/router/app_router.dart       |   7 +
 .../pages/billing_overview_page.dart          | 311 ++++++++++++++++++
 .../providers/billing_provider.dart           |  87 +++++
 .../presentation/pages/settings_page.dart     |  14 +
 packages/gateway/config/kong.yml              |  19 ++
 .../agent-service/src/agent.module.ts         |   7 +-
 .../use-cases/execute-task.use-case.ts        |  57 +++-
 .../domain/entities/usage-record.entity.ts    |  37 +++
 .../ports/outbound/agent-engine.port.ts       |  10 +-
 .../claude-agent-sdk-engine.ts                |  14 +-
 .../engines/claude-api/claude-api-engine.ts   |  28 +-
 .../claude-code-cli/claude-code-engine.ts     |  15 +-
 .../repositories/usage-record.repository.ts   |  24 ++
 .../rest/controllers/agent.controller.ts      |  53 ++-
 .../src/application/services/auth.service.ts  |  17 +
 .../services/billing-service/package.json     |  34 ++
 .../use-cases/aggregate-usage.use-case.ts     | 103 ++++++
 .../use-cases/cancel-subscription.use-case.ts |  30 ++
 .../use-cases/change-plan.use-case.ts         |  86 +++++
 .../use-cases/check-token-quota.use-case.ts   |  82 +++++
 .../create-payment-session.use-case.ts        |  66 ++++
 .../use-cases/create-subscription.use-case.ts |  34 ++
 .../generate-monthly-invoice.use-case.ts      | 122 +++++++
 .../handle-payment-webhook.use-case.ts        | 101 ++++++
 .../billing-service/src/billing.module.ts     | 108 ++++++
 .../domain/entities/invoice-item.entity.ts    |  25 ++
 .../src/domain/entities/invoice.entity.ts     |  48 +++
 .../domain/entities/payment-method.entity.ts  |  28 ++
 .../src/domain/entities/payment.entity.ts     |  39 +++
 .../src/domain/entities/plan.entity.ts        |  55 ++++
 .../domain/entities/subscription.entity.ts    |  42 +++
 .../domain/entities/usage-aggregate.entity.ts |  34 ++
 .../src/domain/ports/payment-provider.port.ts |  44 +++
 .../services/invoice-generator.service.ts     | 134 ++++++++
 .../services/overage-calculator.service.ts    |  23 ++
 .../subscription-lifecycle.service.ts         |  92 ++++++
 .../alipay/alipay.provider.ts                 | 101 ++++++
 .../crypto/crypto.provider.ts                 | 101 ++++++
 .../payment-provider.registry.ts              |  31 ++
 .../stripe/stripe.provider.ts                 |  82 +++++
 .../wechat/wechat-pay.provider.ts             | 156 +++++++++
 .../repositories/invoice.repository.ts        |  78 +++++
 .../repositories/payment.repository.ts        |  59 ++++
 .../repositories/plan.repository.ts           |  37 +++
 .../repositories/subscription.repository.ts   |  41 +++
 .../usage-aggregate.repository.ts             |  68 ++++
 .../scheduler/billing.scheduler.ts            |  26 ++
 .../infrastructure/seed/plan-seed.service.ts  |  63 ++++
 .../rest/controllers/invoice.controller.ts    | 109 ++++++
 .../controllers/payment-method.controller.ts  |  67 ++++
 .../rest/controllers/plan.controller.ts       |  26 ++
 .../controllers/subscription.controller.ts    |  70 ++++
 .../rest/controllers/webhook.controller.ts    |  58 ++++
 packages/services/billing-service/src/main.ts |  33 ++
 .../services/billing-service/tsconfig.json    |  21 ++
 .../rest/controllers/server.controller.ts     |  14 +-
 .../controllers/standing-order.controller.ts  |  16 +-
 .../common/src/constants/event-patterns.ts    |   6 +
 .../src/interfaces/tenant-info.interface.ts   |   4 +
 .../src/utils/tenant-context.service.ts       |  10 +-
 .../002-create-tenant-schema-template.sql     |  18 +
 .../migrations/005-create-billing-tables.sql  | 141 ++++++++
 .../shared/database/src/run-migrations.ts     |   4 +
 .../database/src/tenant-context.middleware.ts |  97 +++++-
 packages/shared/events/src/event-types.ts     |  50 ++-
 72 files changed, 4241 insertions(+), 28 deletions(-)
 create mode 100644 it0-web-admin/src/app/(admin)/billing/invoices/page.tsx
 create mode 100644 it0-web-admin/src/app/(admin)/billing/page.tsx
 create mode 100644 it0-web-admin/src/app/(admin)/billing/plans/page.tsx
 create mode 100644 it0_app/lib/features/billing/presentation/pages/billing_overview_page.dart
 create mode 100644 it0_app/lib/features/billing/presentation/providers/billing_provider.dart
 create mode 100644 packages/services/agent-service/src/domain/entities/usage-record.entity.ts
 create mode 100644 packages/services/agent-service/src/infrastructure/repositories/usage-record.repository.ts
 create mode 100644 packages/services/billing-service/package.json
 create mode 100644 packages/services/billing-service/src/application/use-cases/aggregate-usage.use-case.ts
 create mode 100644 packages/services/billing-service/src/application/use-cases/cancel-subscription.use-case.ts
 create mode 100644 packages/services/billing-service/src/application/use-cases/change-plan.use-case.ts
 create mode 100644 packages/services/billing-service/src/application/use-cases/check-token-quota.use-case.ts
 create mode 100644 packages/services/billing-service/src/application/use-cases/create-payment-session.use-case.ts
 create mode 100644 packages/services/billing-service/src/application/use-cases/create-subscription.use-case.ts
 create mode 100644 packages/services/billing-service/src/application/use-cases/generate-monthly-invoice.use-case.ts
 create mode 100644 packages/services/billing-service/src/application/use-cases/handle-payment-webhook.use-case.ts
 create mode 100644 packages/services/billing-service/src/billing.module.ts
 create mode 100644 packages/services/billing-service/src/domain/entities/invoice-item.entity.ts
 create mode 100644 packages/services/billing-service/src/domain/entities/invoice.entity.ts
 create mode 100644 packages/services/billing-service/src/domain/entities/payment-method.entity.ts
 create mode 100644 packages/services/billing-service/src/domain/entities/payment.entity.ts
 create mode 100644 packages/services/billing-service/src/domain/entities/plan.entity.ts
 create mode 100644 packages/services/billing-service/src/domain/entities/subscription.entity.ts
 create mode 100644 packages/services/billing-service/src/domain/entities/usage-aggregate.entity.ts
 create mode 100644 packages/services/billing-service/src/domain/ports/payment-provider.port.ts
 create mode 100644 packages/services/billing-service/src/domain/services/invoice-generator.service.ts
 create mode 100644 packages/services/billing-service/src/domain/services/overage-calculator.service.ts
 create mode 100644 packages/services/billing-service/src/domain/services/subscription-lifecycle.service.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/payment-providers/alipay/alipay.provider.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/payment-providers/crypto/crypto.provider.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/payment-providers/payment-provider.registry.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/payment-providers/stripe/stripe.provider.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/payment-providers/wechat/wechat-pay.provider.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/repositories/invoice.repository.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/repositories/payment.repository.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/repositories/plan.repository.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/repositories/subscription.repository.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/repositories/usage-aggregate.repository.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/scheduler/billing.scheduler.ts
 create mode 100644 packages/services/billing-service/src/infrastructure/seed/plan-seed.service.ts
 create mode 100644 packages/services/billing-service/src/interfaces/rest/controllers/invoice.controller.ts
 create mode 100644 packages/services/billing-service/src/interfaces/rest/controllers/payment-method.controller.ts
 create mode 100644 packages/services/billing-service/src/interfaces/rest/controllers/plan.controller.ts
 create mode 100644 packages/services/billing-service/src/interfaces/rest/controllers/subscription.controller.ts
 create mode 100644 packages/services/billing-service/src/interfaces/rest/controllers/webhook.controller.ts
 create mode 100644 packages/services/billing-service/src/main.ts
 create mode 100644 packages/services/billing-service/tsconfig.json
 create mode 100644 packages/shared/database/src/migrations/005-create-billing-tables.sql

diff --git a/deploy/docker/docker-compose.yml b/deploy/docker/docker-compose.yml
index c174923..fa3cf63 100644
--- a/deploy/docker/docker-compose.yml
+++ b/deploy/docker/docker-compose.yml
@@ -63,6 +63,8 @@ services:
         condition: service_healthy
       audit-service:
         condition: service_healthy
+      billing-service:
+        condition: service_healthy
       version-service:
         condition: service_healthy
     healthcheck:
@@ -313,6 +315,48 @@ services:
     networks:
       - it0-network
 
+  billing-service:
+    build:
+      context: ../..
+      dockerfile: Dockerfile.service
+      args:
+        SERVICE_NAME: billing-service
+        SERVICE_PORT: 3010
+    container_name: it0-billing-service
+    restart: unless-stopped
+    ports:
+      - "13010:3010"
+    environment:
+      - DB_HOST=postgres
+      - DB_PORT=5432
+      - DB_USERNAME=${POSTGRES_USER:-it0}
+      - DB_PASSWORD=${POSTGRES_PASSWORD:-it0_dev}
+      - DB_DATABASE=${POSTGRES_DB:-it0}
+      - REDIS_URL=redis://redis:6379
+      - BILLING_SERVICE_PORT=3010
+      - STRIPE_SECRET_KEY=${STRIPE_SECRET_KEY}
+      - STRIPE_WEBHOOK_SECRET=${STRIPE_WEBHOOK_SECRET}
+      - ALIPAY_APP_ID=${ALIPAY_APP_ID}
+      - ALIPAY_PRIVATE_KEY=${ALIPAY_PRIVATE_KEY}
+      - WECHAT_MCH_ID=${WECHAT_MCH_ID}
+      - WECHAT_API_KEY_V3=${WECHAT_API_KEY_V3}
+      - WECHAT_APP_ID=${WECHAT_APP_ID}
+      - COINBASE_COMMERCE_API_KEY=${COINBASE_COMMERCE_API_KEY}
+      - COINBASE_COMMERCE_WEBHOOK_SECRET=${COINBASE_COMMERCE_WEBHOOK_SECRET}
+    healthcheck:
+      test: ["CMD-SHELL", "node -e \"require('http').get('http://localhost:3010/',r=>{process.exit(r.statusCode<500?0:1)}).on('error',()=>process.exit(1))\""]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 15s
+    depends_on:
+      postgres:
+        condition: service_healthy
+      redis:
+        condition: service_healthy
+    networks:
+      - it0-network
+
   version-service:
     build:
       context: ../..
diff --git a/it0-web-admin/src/app/(admin)/billing/invoices/page.tsx b/it0-web-admin/src/app/(admin)/billing/invoices/page.tsx
new file mode 100644
index 0000000..b3c315a
--- /dev/null
+++ b/it0-web-admin/src/app/(admin)/billing/invoices/page.tsx
@@ -0,0 +1,146 @@
+'use client';
+
+import { useState } from 'react';
+import { useQuery } from '@tanstack/react-query';
+import Link from 'next/link';
+import { apiClient } from '@/infrastructure/api/api-client';
+import { FileText, Download } from 'lucide-react';
+
+interface Invoice {
+  id: string;
+  invoiceNumber: string;
+  status: string;
+  currency: string;
+  totalAmount: number;
+  amountDue: number;
+  periodStart: string;
+  periodEnd: string;
+  dueDate: string;
+  paidAt: string | null;
+  createdAt: string;
+}
+
+function StatusBadge({ status }: { status: string }) {
+  const colors: Record<string, string> = {
+    paid: 'bg-green-100 text-green-800 dark:bg-green-900/30 dark:text-green-400',
+    open: 'bg-yellow-100 text-yellow-800 dark:bg-yellow-900/30 dark:text-yellow-400',
+    past_due: 'bg-red-100 text-red-800 dark:bg-red-900/30 dark:text-red-400',
+    void: 'bg-gray-100 text-gray-600',
+  };
+  return (
+    <span className={`px-2 py-0.5 rounded text-xs font-medium ${colors[status] ?? 'bg-muted text-muted-foreground'}`}>
+      {status}
+    </span>
+  );
+}
+
+const PAGE_SIZE = 20;
+
+export default function InvoicesPage() {
+  const [page, setPage] = useState(0);
+
+  const { data, isLoading } = useQuery<{ data: Invoice[]; total: number }>({
+    queryKey: ['billing', 'invoices', page],
+    queryFn: () => apiClient(`/api/v1/billing/invoices?limit=${PAGE_SIZE}&offset=${page * PAGE_SIZE}`),
+  });
+
+  const invoices = data?.data ?? [];
+  const total = data?.total ?? 0;
+  const totalPages = Math.ceil(total / PAGE_SIZE);
+
+  return (
+    <div className="space-y-6">
+      <h1 className="text-2xl font-bold flex items-center gap-2">
+        <FileText className="h-6 w-6" /> Invoices
+      </h1>
+
+      <div className="rounded-lg border bg-card overflow-hidden">
+        <div className="overflow-x-auto">
+          <table className="w-full text-sm">
+            <thead className="bg-muted/50 text-muted-foreground">
+              <tr>
+                <th className="text-left p-4 font-medium">Invoice #</th>
+                <th className="text-left p-4 font-medium">Period</th>
+                <th className="text-left p-4 font-medium">Amount</th>
+                <th className="text-left p-4 font-medium">Due Date</th>
+                <th className="text-left p-4 font-medium">Status</th>
+                <th className="p-4" />
+              </tr>
+            </thead>
+            <tbody className="divide-y">
+              {isLoading ? (
+                <tr>
+                  <td colSpan={6} className="p-8 text-center text-muted-foreground">Loading...</td>
+                </tr>
+              ) : invoices.length === 0 ? (
+                <tr>
+                  <td colSpan={6} className="p-8 text-center text-muted-foreground">No invoices found</td>
+                </tr>
+              ) : (
+                invoices.map((inv) => (
+                  <tr key={inv.id} className="hover:bg-muted/30 transition-colors">
+                    <td className="p-4">
+                      <Link href={`/billing/invoices/${inv.id}`} className="text-primary hover:underline font-medium">
+                        {inv.invoiceNumber}
+                      </Link>
+                    </td>
+                    <td className="p-4 text-muted-foreground">
+                      {new Date(inv.periodStart).toLocaleDateString()} – {new Date(inv.periodEnd).toLocaleDateString()}
+                    </td>
+                    <td className="p-4 font-medium">
+                      {inv.currency} {inv.totalAmount.toFixed(2)}
+                    </td>
+                    <td className="p-4 text-muted-foreground">
+                      {new Date(inv.dueDate).toLocaleDateString()}
+                    </td>
+                    <td className="p-4">
+                      <StatusBadge status={inv.status} />
+                    </td>
+                    <td className="p-4 text-right">
+                      {inv.status === 'open' ? (
+                        <Link
+                          href={`/billing/invoices/${inv.id}?pay=1`}
+                          className="text-xs bg-primary text-primary-foreground px-3 py-1.5 rounded-md hover:bg-primary/90"
+                        >
+                          Pay Now
+                        </Link>
+                      ) : (
+                        <button className="p-1.5 rounded hover:bg-muted transition-colors" title="Download">
+                          <Download className="h-4 w-4 text-muted-foreground" />
+                        </button>
+                      )}
+                    </td>
+                  </tr>
+                ))
+              )}
+            </tbody>
+          </table>
+        </div>
+
+        {totalPages > 1 && (
+          <div className="flex items-center justify-between p-4 border-t">
+            <span className="text-sm text-muted-foreground">
+              Page {page + 1} of {totalPages} ({total} total)
+            </span>
+            <div className="flex gap-2">
+              <button
+                onClick={() => setPage((p) => p - 1)}
+                disabled={page === 0}
+                className="px-3 py-1.5 rounded border text-sm disabled:opacity-50"
+              >
+                Previous
+              </button>
+              <button
+                onClick={() => setPage((p) => p + 1)}
+                disabled={page >= totalPages - 1}
+                className="px-3 py-1.5 rounded border text-sm disabled:opacity-50"
+              >
+                Next
+              </button>
+            </div>
+          </div>
+        )}
+      </div>
+    </div>
+  );
+}
diff --git a/it0-web-admin/src/app/(admin)/billing/page.tsx b/it0-web-admin/src/app/(admin)/billing/page.tsx
new file mode 100644
index 0000000..17cdf3a
--- /dev/null
+++ b/it0-web-admin/src/app/(admin)/billing/page.tsx
@@ -0,0 +1,228 @@
+'use client';
+
+import { useQuery } from '@tanstack/react-query';
+import { useTranslation } from 'react-i18next';
+import Link from 'next/link';
+import { apiClient } from '@/infrastructure/api/api-client';
+import { CreditCard, Zap, TrendingUp, AlertCircle, ChevronRight } from 'lucide-react';
+
+interface Subscription {
+  id: string;
+  status: string;
+  plan: { name: string; displayName: string } | null;
+  nextPlan: { name: string; displayName: string } | null;
+  currentPeriodStart: string;
+  currentPeriodEnd: string;
+  trialEndsAt: string | null;
+  cancelAtPeriodEnd: boolean;
+}
+
+interface QuotaStatus {
+  allowed: boolean;
+  remaining: number;
+  usedTokens: number;
+  limitTokens: number;
+  isHardLimit: boolean;
+  overageAllowed: boolean;
+}
+
+interface Invoice {
+  id: string;
+  invoiceNumber: string;
+  status: string;
+  currency: string;
+  totalAmount: number;
+  amountDue: number;
+  periodStart: string;
+  periodEnd: string;
+  dueDate: string;
+  paidAt: string | null;
+  createdAt: string;
+}
+
+function StatusBadge({ status }: { status: string }) {
+  const colors: Record<string, string> = {
+    active: 'bg-green-100 text-green-800 dark:bg-green-900/30 dark:text-green-400',
+    trialing: 'bg-blue-100 text-blue-800 dark:bg-blue-900/30 dark:text-blue-400',
+    past_due: 'bg-yellow-100 text-yellow-800 dark:bg-yellow-900/30 dark:text-yellow-400',
+    cancelled: 'bg-gray-100 text-gray-600 dark:bg-gray-800 dark:text-gray-400',
+    expired: 'bg-red-100 text-red-800 dark:bg-red-900/30 dark:text-red-400',
+    paid: 'bg-green-100 text-green-800 dark:bg-green-900/30 dark:text-green-400',
+    open: 'bg-yellow-100 text-yellow-800 dark:bg-yellow-900/30 dark:text-yellow-400',
+  };
+  return (
+    <span className={`inline-block px-2 py-0.5 rounded text-xs font-medium ${colors[status] ?? 'bg-muted text-muted-foreground'}`}>
+      {status}
+    </span>
+  );
+}
+
+function UsageBar({ used, limit }: { used: number; limit: number }) {
+  const pct = limit <= 0 ? 0 : Math.min(100, (used / limit) * 100);
+  const color = pct >= 90 ? 'bg-red-500' : pct >= 70 ? 'bg-yellow-500' : 'bg-green-500';
+  return (
+    <div className="w-full bg-muted rounded-full h-2">
+      <div className={`${color} h-2 rounded-full transition-all`} style={{ width: `${pct}%` }} />
+    </div>
+  );
+}
+
+function formatTokens(n: number) {
+  if (n >= 1_000_000) return `${(n / 1_000_000).toFixed(2)}M`;
+  if (n >= 1_000) return `${(n / 1_000).toFixed(0)}K`;
+  return `${n}`;
+}
+
+export default function BillingPage() {
+  const { t } = useTranslation();
+
+  const { data: sub } = useQuery<Subscription>({
+    queryKey: ['billing', 'subscription'],
+    queryFn: () => apiClient('/api/v1/billing/subscription'),
+    retry: false,
+  });
+
+  const { data: quota } = useQuery<QuotaStatus>({
+    queryKey: ['billing', 'quota'],
+    queryFn: () => apiClient('/api/v1/billing/usage/current'),
+    refetchInterval: 60_000,
+  });
+
+  const { data: invoicesData } = useQuery<{ data: Invoice[]; total: number }>({
+    queryKey: ['billing', 'invoices'],
+    queryFn: () => apiClient('/api/v1/billing/invoices?limit=5'),
+  });
+
+  const recentInvoices = invoicesData?.data ?? [];
+  const usedPct = quota && quota.limitTokens > 0
+    ? Math.min(100, (quota.usedTokens / quota.limitTokens) * 100)
+    : 0;
+
+  return (
+    <div className="space-y-6">
+      <h1 className="text-2xl font-bold">Billing &amp; Subscription</h1>
+
+      {/* Usage Warning Banner */}
+      {usedPct >= 80 && (
+        <div className="flex items-center gap-3 p-4 rounded-lg bg-yellow-50 border border-yellow-200 dark:bg-yellow-900/20 dark:border-yellow-800">
+          <AlertCircle className="h-5 w-5 text-yellow-600 flex-shrink-0" />
+          <span className="text-sm text-yellow-800 dark:text-yellow-300">
+            You have used {usedPct.toFixed(0)}% of your monthly token quota.{' '}
+            {usedPct >= 100 ? 'Limit reached — agent tasks are blocked.' : 'Consider upgrading your plan.'}
+          </span>
+          <Link href="/billing/plans" className="ml-auto text-sm font-medium text-yellow-800 dark:text-yellow-300 underline whitespace-nowrap">
+            Upgrade
+          </Link>
+        </div>
+      )}
+
+      <div className="grid grid-cols-1 md:grid-cols-2 gap-6">
+        {/* Subscription Card */}
+        <div className="rounded-lg border bg-card p-6 space-y-4">
+          <div className="flex items-center justify-between">
+            <div className="flex items-center gap-2">
+              <CreditCard className="h-5 w-5 text-muted-foreground" />
+              <h2 className="font-semibold">Current Plan</h2>
+            </div>
+            <Link href="/billing/plans" className="text-sm text-primary flex items-center gap-1 hover:underline">
+              Change <ChevronRight className="h-4 w-4" />
+            </Link>
+          </div>
+
+          {sub ? (
+            <div className="space-y-2">
+              <div className="flex items-center gap-3">
+                <span className="text-2xl font-bold capitalize">{sub.plan?.displayName ?? 'Unknown'}</span>
+                <StatusBadge status={sub.status} />
+              </div>
+              {sub.trialEndsAt && sub.status === 'trialing' && (
+                <p className="text-sm text-muted-foreground">
+                  Trial ends {new Date(sub.trialEndsAt).toLocaleDateString()}
+                </p>
+              )}
+              {sub.cancelAtPeriodEnd && (
+                <p className="text-sm text-yellow-600 dark:text-yellow-400">
+                  Cancels on {new Date(sub.currentPeriodEnd).toLocaleDateString()}
+                </p>
+              )}
+              {sub.nextPlan && (
+                <p className="text-sm text-muted-foreground">
+                  Downgrade to <strong>{sub.nextPlan.displayName}</strong> on {new Date(sub.currentPeriodEnd).toLocaleDateString()}
+                </p>
+              )}
+              <p className="text-xs text-muted-foreground">
+                Period: {new Date(sub.currentPeriodStart).toLocaleDateString()} – {new Date(sub.currentPeriodEnd).toLocaleDateString()}
+              </p>
+            </div>
+          ) : (
+            <p className="text-muted-foreground text-sm">No active subscription</p>
+          )}
+        </div>
+
+        {/* Token Usage Card */}
+        <div className="rounded-lg border bg-card p-6 space-y-4">
+          <div className="flex items-center gap-2">
+            <Zap className="h-5 w-5 text-muted-foreground" />
+            <h2 className="font-semibold">This Month&apos;s Token Usage</h2>
+          </div>
+
+          {quota ? (
+            <div className="space-y-3">
+              <div className="flex justify-between text-sm">
+                <span className="font-medium">{formatTokens(quota.usedTokens)} used</span>
+                <span className="text-muted-foreground">
+                  {quota.limitTokens === -1 ? 'Unlimited' : `${formatTokens(quota.limitTokens)} limit`}
+                </span>
+              </div>
+              {quota.limitTokens !== -1 && (
+                <UsageBar used={quota.usedTokens} limit={quota.limitTokens} />
+              )}
+              <div className="flex justify-between text-xs text-muted-foreground">
+                <span>{usedPct.toFixed(1)}%</span>
+                {quota.overageAllowed && usedPct > 100 && (
+                  <span className="text-yellow-600">Overage charges apply</span>
+                )}
+              </div>
+            </div>
+          ) : (
+            <p className="text-muted-foreground text-sm">Loading usage data...</p>
+          )}
+        </div>
+      </div>
+
+      {/* Recent Invoices */}
+      <div className="rounded-lg border bg-card">
+        <div className="flex items-center justify-between p-6 border-b">
+          <div className="flex items-center gap-2">
+            <TrendingUp className="h-5 w-5 text-muted-foreground" />
+            <h2 className="font-semibold">Recent Invoices</h2>
+          </div>
+          <Link href="/billing/invoices" className="text-sm text-primary hover:underline flex items-center gap-1">
+            View all <ChevronRight className="h-4 w-4" />
+          </Link>
+        </div>
+
+        {recentInvoices.length === 0 ? (
+          <div className="p-6 text-center text-muted-foreground text-sm">No invoices yet</div>
+        ) : (
+          <div className="divide-y">
+            {recentInvoices.map((inv) => (
+              <Link key={inv.id} href={`/billing/invoices/${inv.id}`} className="flex items-center justify-between p-4 hover:bg-muted/50 transition-colors">
+                <div>
+                  <p className="text-sm font-medium">{inv.invoiceNumber}</p>
+                  <p className="text-xs text-muted-foreground">
+                    {new Date(inv.periodStart).toLocaleDateString()} – {new Date(inv.periodEnd).toLocaleDateString()}
+                  </p>
+                </div>
+                <div className="flex items-center gap-3">
+                  <span className="text-sm font-medium">{inv.currency} {inv.totalAmount.toFixed(2)}</span>
+                  <StatusBadge status={inv.status} />
+                </div>
+              </Link>
+            ))}
+          </div>
+        )}
+      </div>
+    </div>
+  );
+}
diff --git a/it0-web-admin/src/app/(admin)/billing/plans/page.tsx b/it0-web-admin/src/app/(admin)/billing/plans/page.tsx
new file mode 100644
index 0000000..b02a9b4
--- /dev/null
+++ b/it0-web-admin/src/app/(admin)/billing/plans/page.tsx
@@ -0,0 +1,214 @@
+'use client';
+
+import { useState } from 'react';
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
+import { useRouter } from 'next/navigation';
+import { apiClient } from '@/infrastructure/api/api-client';
+import { Check, Zap } from 'lucide-react';
+
+interface Plan {
+  id: string;
+  name: string;
+  displayName: string;
+  monthlyPriceUsd: number;
+  monthlyPriceCny: number;
+  includedTokensPerMonth: number;
+  overageRateUsdPerMToken: number;
+  maxServers: number;
+  maxUsers: number;
+  maxStandingOrders: number;
+  hardLimitPercent: number;
+  trialDays: number;
+}
+
+interface Subscription {
+  plan: { name: string } | null;
+  status: string;
+}
+
+function formatLimit(n: number) {
+  return n === -1 ? 'Unlimited' : n.toLocaleString();
+}
+
+function formatTokens(n: number) {
+  if (n >= 1_000_000) return `${(n / 1_000_000).toFixed(0)}M`;
+  if (n >= 1_000) return `${(n / 1_000).toFixed(0)}K`;
+  return `${n}`;
+}
+
+const PLAN_FEATURES: Record<string, string[]> = {
+  free: ['100K tokens/month', 'Up to 5 servers', 'Up to 3 users', 'Up to 10 standing orders', 'Hard limit at 100%'],
+  pro: ['1M tokens/month', 'Up to 50 servers', 'Up to 20 users', 'Up to 100 standing orders', 'Soft limit at 150%', 'Overage at $8/MTok', '14-day trial'],
+  enterprise: ['10M tokens/month', 'Unlimited servers', 'Unlimited users', 'Unlimited standing orders', 'No hard limit', 'Overage at $5/MTok', '14-day trial'],
+};
+
+export default function PlansPage() {
+  const queryClient = useQueryClient();
+  const router = useRouter();
+  const [currency, setCurrency] = useState<'USD' | 'CNY'>('USD');
+  const [selectedPlan, setSelectedPlan] = useState<string | null>(null);
+
+  const { data: plans = [] } = useQuery<Plan[]>({
+    queryKey: ['billing', 'plans'],
+    queryFn: () => apiClient('/api/v1/billing/plans'),
+  });
+
+  const { data: sub } = useQuery<Subscription>({
+    queryKey: ['billing', 'subscription'],
+    queryFn: () => apiClient('/api/v1/billing/subscription'),
+    retry: false,
+  });
+
+  const currentPlanName = sub?.plan?.name;
+
+  const upgradeMutation = useMutation({
+    mutationFn: (planName: string) =>
+      apiClient('/api/v1/billing/subscription/upgrade', {
+        method: 'POST',
+        body: { planName, currency },
+      }),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['billing'] });
+      router.push('/billing');
+    },
+  });
+
+  const handleSelectPlan = (planName: string) => {
+    if (planName === currentPlanName) return;
+    setSelectedPlan(planName);
+  };
+
+  const handleConfirm = () => {
+    if (!selectedPlan) return;
+    upgradeMutation.mutate(selectedPlan);
+  };
+
+  return (
+    <div className="space-y-6">
+      <div className="flex items-center justify-between">
+        <h1 className="text-2xl font-bold">Choose a Plan</h1>
+        <div className="flex items-center gap-2 text-sm">
+          <button
+            onClick={() => setCurrency('USD')}
+            className={`px-3 py-1 rounded-full ${currency === 'USD' ? 'bg-primary text-primary-foreground' : 'bg-muted'}`}
+          >
+            USD
+          </button>
+          <button
+            onClick={() => setCurrency('CNY')}
+            className={`px-3 py-1 rounded-full ${currency === 'CNY' ? 'bg-primary text-primary-foreground' : 'bg-muted'}`}
+          >
+            CNY
+          </button>
+        </div>
+      </div>
+
+      <div className="grid grid-cols-1 md:grid-cols-3 gap-6">
+        {plans.map((plan) => {
+          const isCurrent = plan.name === currentPlanName;
+          const isSelected = plan.name === selectedPlan;
+          const price = currency === 'CNY' ? plan.monthlyPriceCny : plan.monthlyPriceUsd;
+          const symbol = currency === 'CNY' ? '¥' : '$';
+          const features = PLAN_FEATURES[plan.name] ?? [];
+          const isEnterprise = plan.name === 'enterprise';
+
+          return (
+            <div
+              key={plan.id}
+              onClick={() => handleSelectPlan(plan.name)}
+              className={`relative rounded-xl border-2 p-6 cursor-pointer transition-all space-y-4 ${
+                isEnterprise ? 'border-primary' : 'border-border'
+              } ${isSelected ? 'ring-2 ring-primary ring-offset-2' : ''} ${
+                isCurrent ? 'opacity-70 cursor-default' : 'hover:border-primary/50'
+              }`}
+            >
+              {isEnterprise && (
+                <div className="absolute -top-3 left-1/2 -translate-x-1/2">
+                  <span className="bg-primary text-primary-foreground text-xs font-bold px-3 py-1 rounded-full">
+                    MOST POPULAR
+                  </span>
+                </div>
+              )}
+
+              {isCurrent && (
+                <div className="absolute top-3 right-3">
+                  <span className="bg-green-100 text-green-800 dark:bg-green-900/30 dark:text-green-400 text-xs font-medium px-2 py-0.5 rounded-full">
+                    Current
+                  </span>
+                </div>
+              )}
+
+              <div>
+                <h3 className="text-xl font-bold">{plan.displayName}</h3>
+                <div className="flex items-end gap-1 mt-2">
+                  <span className="text-3xl font-bold">{symbol}{price.toFixed(2)}</span>
+                  <span className="text-muted-foreground text-sm mb-1">/month</span>
+                </div>
+                {plan.trialDays > 0 && (
+                  <p className="text-xs text-primary mt-1">{plan.trialDays}-day free trial</p>
+                )}
+              </div>
+
+              <div className="border-t pt-4 space-y-2">
+                <div className="flex items-center gap-2 text-sm font-medium">
+                  <Zap className="h-4 w-4 text-primary" />
+                  {formatTokens(plan.includedTokensPerMonth)} tokens/month
+                </div>
+                {plan.overageRateUsdPerMToken > 0 && (
+                  <p className="text-xs text-muted-foreground pl-6">
+                    Overage: {currency === 'CNY'
+                      ? `¥${(plan.overageRateUsdPerMToken * 7.2).toFixed(2)}`
+                      : `$${plan.overageRateUsdPerMToken.toFixed(2)}`}/MTok
+                  </p>
+                )}
+              </div>
+
+              <ul className="space-y-1.5">
+                {features.map((f) => (
+                  <li key={f} className="flex items-center gap-2 text-sm">
+                    <Check className="h-4 w-4 text-green-500 flex-shrink-0" />
+                    {f}
+                  </li>
+                ))}
+              </ul>
+
+              {!isCurrent && (
+                <button
+                  onClick={(e) => { e.stopPropagation(); handleSelectPlan(plan.name); }}
+                  className={`w-full py-2 rounded-lg text-sm font-medium transition-colors ${
+                    isSelected
+                      ? 'bg-primary text-primary-foreground'
+                      : 'bg-muted hover:bg-primary/10'
+                  }`}
+                >
+                  {isSelected ? 'Selected' : plan.name === 'free' ? 'Downgrade' : 'Upgrade'}
+                </button>
+              )}
+            </div>
+          );
+        })}
+      </div>
+
+      {selectedPlan && (
+        <div className="flex justify-end gap-3 pt-4">
+          <button onClick={() => setSelectedPlan(null)} className="px-4 py-2 rounded-lg border text-sm">
+            Cancel
+          </button>
+          <button
+            onClick={handleConfirm}
+            disabled={upgradeMutation.isPending}
+            className="px-6 py-2 rounded-lg bg-primary text-primary-foreground text-sm font-medium disabled:opacity-50"
+          >
+            {upgradeMutation.isPending ? 'Processing...' : `Switch to ${selectedPlan}`}
+          </button>
+        </div>
+      )}
+
+      {upgradeMutation.isError && (
+        <p className="text-sm text-red-500 text-center">
+          Failed to change plan. Please try again.
+        </p>
+      )}
+    </div>
+  );
+}
diff --git a/it0-web-admin/src/i18n/locales/en/sidebar.json b/it0-web-admin/src/i18n/locales/en/sidebar.json
index 1ea6599..3042149 100644
--- a/it0-web-admin/src/i18n/locales/en/sidebar.json
+++ b/it0-web-admin/src/i18n/locales/en/sidebar.json
@@ -26,6 +26,10 @@
   "logs": "Logs",
   "sessionReplay": "Session Replay",
   "communication": "Communication",
+  "billing": "Billing",
+  "billingOverview": "Overview",
+  "billingPlans": "Plans",
+  "billingInvoices": "Invoices",
   "tenants": "Tenants",
   "users": "Users",
   "settings": "Settings",
diff --git a/it0-web-admin/src/i18n/locales/zh/sidebar.json b/it0-web-admin/src/i18n/locales/zh/sidebar.json
index df7def3..a06c1b9 100644
--- a/it0-web-admin/src/i18n/locales/zh/sidebar.json
+++ b/it0-web-admin/src/i18n/locales/zh/sidebar.json
@@ -26,6 +26,10 @@
   "logs": "日志",
   "sessionReplay": "会话回放",
   "communication": "通讯",
+  "billing": "账单",
+  "billingOverview": "总览",
+  "billingPlans": "套餐",
+  "billingInvoices": "账单列表",
   "tenants": "租户",
   "users": "用户",
   "settings": "设置",
diff --git a/it0-web-admin/src/presentation/components/layout/sidebar.tsx b/it0-web-admin/src/presentation/components/layout/sidebar.tsx
index 1f89a7e..c743f77 100644
--- a/it0-web-admin/src/presentation/components/layout/sidebar.tsx
+++ b/it0-web-admin/src/presentation/components/layout/sidebar.tsx
@@ -22,6 +22,7 @@ import {
   ChevronRight,
   PanelLeftClose,
   PanelLeft,
+  CreditCard,
 } from 'lucide-react';
 
 /* ---------- Sidebar context for collapse state ---------- */
@@ -148,6 +149,17 @@ export function Sidebar() {
       ],
     },
     { key: 'communication', label: t('communication'), href: '/communication', icon: <MessageSquare className={iconClass} /> },
+    {
+      key: 'billing',
+      label: t('billing'),
+      href: '/billing',
+      icon: <CreditCard className={iconClass} />,
+      children: [
+        { label: t('billingOverview'), href: '/billing' },
+        { label: t('billingPlans'), href: '/billing/plans' },
+        { label: t('billingInvoices'), href: '/billing/invoices' },
+      ],
+    },
     { key: 'tenants', label: t('tenants'), href: '/tenants', icon: <Building2 className={iconClass} /> },
     { key: 'users', label: t('users'), href: '/users', icon: <Users className={iconClass} /> },
     { key: 'settings', label: t('settings'), href: '/settings', icon: <Settings className={iconClass} /> },
diff --git a/it0_app/lib/core/router/app_router.dart b/it0_app/lib/core/router/app_router.dart
index 398cb64..b7f8fe4 100644
--- a/it0_app/lib/core/router/app_router.dart
+++ b/it0_app/lib/core/router/app_router.dart
@@ -16,6 +16,7 @@ import '../../features/alerts/presentation/pages/alerts_page.dart';
 import '../../features/settings/presentation/pages/settings_page.dart';
 import '../../features/terminal/presentation/pages/terminal_page.dart';
 import '../../features/notifications/presentation/providers/notification_providers.dart';
+import '../../features/billing/presentation/pages/billing_overview_page.dart';
 
 final routerProvider = Provider<GoRouter>((ref) {
   return GoRouter(
@@ -67,6 +68,12 @@ final routerProvider = Provider<GoRouter>((ref) {
           GoRoute(
             path: '/settings',
             builder: (context, state) => const SettingsPage(),
+            routes: [
+              GoRoute(
+                path: 'billing',
+                builder: (context, state) => const BillingOverviewPage(),
+              ),
+            ],
           ),
         ],
       ),
diff --git a/it0_app/lib/features/billing/presentation/pages/billing_overview_page.dart b/it0_app/lib/features/billing/presentation/pages/billing_overview_page.dart
new file mode 100644
index 0000000..7834236
--- /dev/null
+++ b/it0_app/lib/features/billing/presentation/pages/billing_overview_page.dart
@@ -0,0 +1,311 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../../../../core/theme/app_colors.dart';
+import '../providers/billing_provider.dart';
+
+class BillingOverviewPage extends ConsumerWidget {
+  const BillingOverviewPage({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final billingAsync = ref.watch(billingOverviewProvider);
+    final theme = Theme.of(context);
+    final isDark = theme.brightness == Brightness.dark;
+    final cardColor = isDark ? AppColors.surface : Colors.white;
+
+    return Scaffold(
+      appBar: AppBar(title: const Text('订阅与用量')),
+      body: billingAsync.when(
+        loading: () => const Center(child: CircularProgressIndicator()),
+        error: (e, _) => Center(child: Text('加载失败: $e')),
+        data: (billing) => ListView(
+          padding: const EdgeInsets.all(16),
+          children: [
+            // Subscription Card
+            _SubscriptionCard(
+              planName: billing.planDisplayName,
+              status: billing.subscriptionStatus,
+              periodEnd: billing.currentPeriodEnd,
+              cardColor: cardColor,
+              theme: theme,
+            ),
+            const SizedBox(height: 16),
+
+            // Token Usage Card
+            _UsageCard(
+              usedTokens: billing.usedTokens,
+              limitTokens: billing.limitTokens,
+              cardColor: cardColor,
+              theme: theme,
+            ),
+            const SizedBox(height: 16),
+
+            // Recent Invoice Card
+            if (billing.latestInvoice != null)
+              _InvoiceCard(
+                invoice: billing.latestInvoice!,
+                cardColor: cardColor,
+                theme: theme,
+              ),
+            const SizedBox(height: 24),
+
+            // Upgrade Button
+            if (billing.subscriptionStatus != 'enterprise')
+              ElevatedButton.icon(
+                onPressed: () {
+                  // Open web admin billing/plans in browser
+                  // or show a dialog for now
+                  _showUpgradeDialog(context);
+                },
+                icon: const Icon(Icons.upgrade),
+                label: const Text('升级套餐'),
+                style: ElevatedButton.styleFrom(
+                  minimumSize: const Size(double.infinity, 48),
+                  backgroundColor: AppColors.primary,
+                  foregroundColor: Colors.white,
+                  shape: RoundedRectangleBorder(
+                    borderRadius: BorderRadius.circular(12),
+                  ),
+                ),
+              ),
+          ],
+        ),
+      ),
+    );
+  }
+
+  void _showUpgradeDialog(BuildContext context) {
+    showDialog(
+      context: context,
+      builder: (ctx) => AlertDialog(
+        title: const Text('升级套餐'),
+        content: const Text('请前往 Web 管理后台 → 账单 → 套餐 完成升级。'),
+        actions: [
+          TextButton(
+            onPressed: () => Navigator.of(ctx).pop(),
+            child: const Text('知道了'),
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+class _SubscriptionCard extends StatelessWidget {
+  final String planName;
+  final String status;
+  final DateTime? periodEnd;
+  final Color cardColor;
+  final ThemeData theme;
+
+  const _SubscriptionCard({
+    required this.planName,
+    required this.status,
+    required this.periodEnd,
+    required this.cardColor,
+    required this.theme,
+  });
+
+  Color _statusColor(String status) => switch (status) {
+        'active' => Colors.green,
+        'trialing' => Colors.blue,
+        'past_due' => Colors.orange,
+        _ => Colors.grey,
+      };
+
+  String _statusLabel(String status) => switch (status) {
+        'active' => '正常',
+        'trialing' => '试用期',
+        'past_due' => '待付款',
+        'cancelled' => '已取消',
+        'expired' => '已过期',
+        _ => status,
+      };
+
+  @override
+  Widget build(BuildContext context) {
+    return Card(
+      color: cardColor,
+      elevation: 0,
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(16),
+        side: BorderSide(color: Colors.grey.withOpacity(0.15)),
+      ),
+      child: Padding(
+        padding: const EdgeInsets.all(20),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            Row(
+              children: [
+                const Icon(Icons.credit_card, size: 20, color: AppColors.primary),
+                const SizedBox(width: 8),
+                Text('当前套餐', style: theme.textTheme.bodySmall?.copyWith(color: Colors.grey)),
+              ],
+            ),
+            const SizedBox(height: 12),
+            Row(
+              crossAxisAlignment: CrossAxisAlignment.end,
+              children: [
+                Text(
+                  planName,
+                  style: theme.textTheme.headlineMedium?.copyWith(fontWeight: FontWeight.bold),
+                ),
+                const SizedBox(width: 10),
+                Container(
+                  padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 3),
+                  decoration: BoxDecoration(
+                    color: _statusColor(status).withOpacity(0.1),
+                    borderRadius: BorderRadius.circular(20),
+                  ),
+                  child: Text(
+                    _statusLabel(status),
+                    style: TextStyle(fontSize: 12, color: _statusColor(status), fontWeight: FontWeight.w600),
+                  ),
+                ),
+              ],
+            ),
+            if (periodEnd != null) ...[
+              const SizedBox(height: 6),
+              Text(
+                '当期结束：${_formatDate(periodEnd!)}',
+                style: theme.textTheme.bodySmall?.copyWith(color: Colors.grey),
+              ),
+            ],
+          ],
+        ),
+      ),
+    );
+  }
+
+  String _formatDate(DateTime d) => '${d.year}-${d.month.toString().padLeft(2, '0')}-${d.day.toString().padLeft(2, '0')}';
+}
+
+class _UsageCard extends StatelessWidget {
+  final int usedTokens;
+  final int limitTokens;
+  final Color cardColor;
+  final ThemeData theme;
+
+  const _UsageCard({
+    required this.usedTokens,
+    required this.limitTokens,
+    required this.cardColor,
+    required this.theme,
+  });
+
+  String _formatTokens(int n) {
+    if (n >= 1000000) return '${(n / 1000000).toStringAsFixed(2)}M';
+    if (n >= 1000) return '${(n / 1000).toStringAsFixed(0)}K';
+    return '$n';
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final isUnlimited = limitTokens == -1;
+    final pct = isUnlimited ? 0.0 : (usedTokens / limitTokens).clamp(0.0, 1.0);
+    final barColor = pct >= 0.9 ? Colors.red : pct >= 0.7 ? Colors.orange : Colors.green;
+
+    return Card(
+      color: cardColor,
+      elevation: 0,
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(16),
+        side: BorderSide(color: Colors.grey.withOpacity(0.15)),
+      ),
+      child: Padding(
+        padding: const EdgeInsets.all(20),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            Row(
+              children: [
+                const Icon(Icons.bolt, size: 20, color: AppColors.primary),
+                const SizedBox(width: 8),
+                Text('本月 Token 用量', style: theme.textTheme.bodySmall?.copyWith(color: Colors.grey)),
+              ],
+            ),
+            const SizedBox(height: 16),
+            Row(
+              mainAxisAlignment: MainAxisAlignment.spaceBetween,
+              children: [
+                Text(
+                  _formatTokens(usedTokens),
+                  style: theme.textTheme.titleLarge?.copyWith(fontWeight: FontWeight.bold),
+                ),
+                Text(
+                  isUnlimited ? '不限量' : _formatTokens(limitTokens),
+                  style: theme.textTheme.bodyMedium?.copyWith(color: Colors.grey),
+                ),
+              ],
+            ),
+            if (!isUnlimited) ...[
+              const SizedBox(height: 10),
+              ClipRRect(
+                borderRadius: BorderRadius.circular(4),
+                child: LinearProgressIndicator(
+                  value: pct,
+                  minHeight: 6,
+                  backgroundColor: Colors.grey.withOpacity(0.2),
+                  valueColor: AlwaysStoppedAnimation(barColor),
+                ),
+              ),
+              const SizedBox(height: 6),
+              Text(
+                '${(pct * 100).toStringAsFixed(1)}%',
+                style: theme.textTheme.bodySmall?.copyWith(color: Colors.grey),
+              ),
+            ],
+          ],
+        ),
+      ),
+    );
+  }
+}
+
+class _InvoiceCard extends StatelessWidget {
+  final LatestInvoice invoice;
+  final Color cardColor;
+  final ThemeData theme;
+
+  const _InvoiceCard({
+    required this.invoice,
+    required this.cardColor,
+    required this.theme,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return Card(
+      color: cardColor,
+      elevation: 0,
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(16),
+        side: BorderSide(color: Colors.grey.withOpacity(0.15)),
+      ),
+      child: ListTile(
+        contentPadding: const EdgeInsets.symmetric(horizontal: 20, vertical: 8),
+        leading: const Icon(Icons.receipt_long, color: AppColors.primary),
+        title: Text(invoice.invoiceNumber, style: const TextStyle(fontWeight: FontWeight.w600)),
+        subtitle: Text('${invoice.currency} ${invoice.amount.toStringAsFixed(2)}', style: const TextStyle(fontSize: 13)),
+        trailing: Container(
+          padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 4),
+          decoration: BoxDecoration(
+            color: invoice.status == 'paid'
+                ? Colors.green.withOpacity(0.1)
+                : Colors.orange.withOpacity(0.1),
+            borderRadius: BorderRadius.circular(20),
+          ),
+          child: Text(
+            invoice.status == 'paid' ? '已付款' : '待付款',
+            style: TextStyle(
+              fontSize: 12,
+              fontWeight: FontWeight.w600,
+              color: invoice.status == 'paid' ? Colors.green : Colors.orange,
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}
diff --git a/it0_app/lib/features/billing/presentation/providers/billing_provider.dart b/it0_app/lib/features/billing/presentation/providers/billing_provider.dart
new file mode 100644
index 0000000..d103796
--- /dev/null
+++ b/it0_app/lib/features/billing/presentation/providers/billing_provider.dart
@@ -0,0 +1,87 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import '../../../../core/network/dio_client.dart';
+
+class LatestInvoice {
+  final String invoiceNumber;
+  final String status;
+  final String currency;
+  final double amount;
+
+  const LatestInvoice({
+    required this.invoiceNumber,
+    required this.status,
+    required this.currency,
+    required this.amount,
+  });
+
+  factory LatestInvoice.fromJson(Map<String, dynamic> json) => LatestInvoice(
+        invoiceNumber: json['invoiceNumber'] as String? ?? '',
+        status: json['status'] as String? ?? '',
+        currency: json['currency'] as String? ?? 'USD',
+        amount: (json['totalAmount'] as num?)?.toDouble() ?? 0,
+      );
+}
+
+class BillingOverview {
+  final String planDisplayName;
+  final String subscriptionStatus;
+  final DateTime? currentPeriodEnd;
+  final DateTime? trialEndsAt;
+  final int usedTokens;
+  final int limitTokens;
+  final bool overageAllowed;
+  final LatestInvoice? latestInvoice;
+
+  const BillingOverview({
+    required this.planDisplayName,
+    required this.subscriptionStatus,
+    required this.currentPeriodEnd,
+    required this.trialEndsAt,
+    required this.usedTokens,
+    required this.limitTokens,
+    required this.overageAllowed,
+    required this.latestInvoice,
+  });
+}
+
+final billingOverviewProvider = FutureProvider<BillingOverview>((ref) async {
+  final dio = ref.read(dioClientProvider);
+
+  // Fetch subscription, quota, and recent invoice (ignore 404s gracefully)
+  Map<String, dynamic>? sub;
+  Map<String, dynamic>? quota;
+  Map<String, dynamic>? invoicesData;
+
+  try {
+    final r = await dio.get('/api/v1/billing/subscription');
+    sub = r.data as Map<String, dynamic>?;
+  } catch (_) {}
+
+  try {
+    final r = await dio.get('/api/v1/billing/usage/current');
+    quota = r.data as Map<String, dynamic>?;
+  } catch (_) {}
+
+  try {
+    final r = await dio.get('/api/v1/billing/invoices?limit=1');
+    invoicesData = r.data as Map<String, dynamic>?;
+  } catch (_) {}
+
+  final invoices = (invoicesData?['data'] as List?)?.cast<Map<String, dynamic>>() ?? [];
+  final latestInvoice = invoices.isNotEmpty ? LatestInvoice.fromJson(invoices.first) : null;
+
+  return BillingOverview(
+    planDisplayName: ((sub?['plan'] as Map<String, dynamic>?)?['displayName'] as String?) ?? 'Free',
+    subscriptionStatus: sub?['status'] as String? ?? 'unknown',
+    currentPeriodEnd: sub?['currentPeriodEnd'] != null
+        ? DateTime.tryParse(sub!['currentPeriodEnd'] as String)
+        : null,
+    trialEndsAt: sub?['trialEndsAt'] != null
+        ? DateTime.tryParse(sub!['trialEndsAt'] as String)
+        : null,
+    usedTokens: quota?['usedTokens'] as int? ?? 0,
+    limitTokens: quota?['limitTokens'] as int? ?? 0,
+    overageAllowed: quota?['overageAllowed'] as bool? ?? false,
+    latestInvoice: latestInvoice,
+  );
+});
diff --git a/it0_app/lib/features/settings/presentation/pages/settings_page.dart b/it0_app/lib/features/settings/presentation/pages/settings_page.dart
index b8f55ee..7ca338c 100644
--- a/it0_app/lib/features/settings/presentation/pages/settings_page.dart
+++ b/it0_app/lib/features/settings/presentation/pages/settings_page.dart
@@ -148,6 +148,20 @@ class _SettingsPageState extends ConsumerState<SettingsPage> {
           ),
           const SizedBox(height: 24),
 
+          // ===== Billing Group =====
+          _SettingsGroup(
+            cardColor: cardColor,
+            children: [
+              _SettingsRow(
+                icon: Icons.credit_card_outlined,
+                iconBg: const Color(0xFF10B981),
+                title: '订阅与用量',
+                onTap: () => context.push('/settings/billing'),
+              ),
+            ],
+          ),
+          const SizedBox(height: 24),
+
           // ===== Security Group =====
           _SettingsGroup(
             cardColor: cardColor,
diff --git a/packages/gateway/config/kong.yml b/packages/gateway/config/kong.yml
index 7556197..9ce0dea 100644
--- a/packages/gateway/config/kong.yml
+++ b/packages/gateway/config/kong.yml
@@ -121,6 +121,18 @@ services:
           - /api/v1/versions
         strip_path: false
 
+  - name: billing-service
+    url: http://billing-service:3010
+    routes:
+      - name: billing-routes
+        paths:
+          - /api/v1/billing
+        strip_path: false
+      - name: billing-webhooks
+        paths:
+          - /api/v1/billing/webhooks
+        strip_path: false
+
 plugins:
   # ===== Global plugins (apply to ALL routes) =====
   - name: cors
@@ -219,6 +231,13 @@ plugins:
       claims_to_verify:
         - exp
 
+  - name: jwt
+    route: billing-routes
+    config:
+      key_claim_name: kid
+      claims_to_verify:
+        - exp
+
   - name: jwt
     route: admin-routes
     config:
diff --git a/packages/services/agent-service/src/agent.module.ts b/packages/services/agent-service/src/agent.module.ts
index b32f678..7d2caaf 100644
--- a/packages/services/agent-service/src/agent.module.ts
+++ b/packages/services/agent-service/src/agent.module.ts
@@ -37,11 +37,14 @@ import { AgentConfig } from './domain/entities/agent-config.entity';
 import { HookScript } from './domain/entities/hook-script.entity';
 import { VoiceConfig } from './domain/entities/voice-config.entity';
 import { ConversationMessage } from './domain/entities/conversation-message.entity';
+import { UsageRecord } from './domain/entities/usage-record.entity';
 import { MessageRepository } from './infrastructure/repositories/message.repository';
 import { VoiceConfigRepository } from './infrastructure/repositories/voice-config.repository';
+import { UsageRecordRepository } from './infrastructure/repositories/usage-record.repository';
 import { VoiceConfigService } from './infrastructure/services/voice-config.service';
 import { VoiceConfigController } from './interfaces/rest/controllers/voice-config.controller';
 import { ConversationContextService } from './domain/services/conversation-context.service';
+import { EventPublisherService } from './infrastructure/messaging/event-publisher.service';
 
 @Module({
   imports: [
@@ -50,7 +53,7 @@ import { ConversationContextService } from './domain/services/conversation-conte
     TypeOrmModule.forFeature([
       AgentSession, AgentTask, CommandRecord, StandingOrderRef,
       TenantAgentConfig, AgentConfig, HookScript, VoiceConfig,
-      ConversationMessage,
+      ConversationMessage, UsageRecord,
     ]),
   ],
   controllers: [
@@ -72,6 +75,7 @@ import { ConversationContextService } from './domain/services/conversation-conte
     SessionRepository,
     TaskRepository,
     MessageRepository,
+    UsageRecordRepository,
     TenantAgentConfigRepository,
     AgentConfigRepository,
     VoiceConfigRepository,
@@ -81,6 +85,7 @@ import { ConversationContextService } from './domain/services/conversation-conte
     VoiceConfigService,
     AgentSkillService,
     HookScriptService,
+    EventPublisherService,
   ],
 })
 export class AgentModule {}
diff --git a/packages/services/agent-service/src/application/use-cases/execute-task.use-case.ts b/packages/services/agent-service/src/application/use-cases/execute-task.use-case.ts
index e5d0649..90fae10 100644
--- a/packages/services/agent-service/src/application/use-cases/execute-task.use-case.ts
+++ b/packages/services/agent-service/src/application/use-cases/execute-task.use-case.ts
@@ -2,14 +2,16 @@ import { Injectable, Logger } from '@nestjs/common';
 import { EngineRegistry } from '../../infrastructure/engines/engine-registry';
 import { SessionRepository } from '../../infrastructure/repositories/session.repository';
 import { TaskRepository } from '../../infrastructure/repositories/task.repository';
+import { UsageRecordRepository } from '../../infrastructure/repositories/usage-record.repository';
 import { AgentStreamGateway } from '../../interfaces/ws/agent-stream.gateway';
 import { AgentSession } from '../../domain/entities/agent-session.entity';
 import { AgentTask } from '../../domain/entities/agent-task.entity';
+import { UsageRecord } from '../../domain/entities/usage-record.entity';
 import { TaskStatus } from '../../domain/value-objects/task-status.vo';
 import { EngineStreamEvent } from '../../domain/ports/outbound/agent-engine.port';
 import { EventPublisherPort } from '../../domain/ports/outbound/event-publisher.port';
 import { ExecuteTaskDto } from '../dto/execute-task.dto';
-import { TaskResultDto } from '../dto/task-result.dto';
+import { EventPatterns } from '@it0/common';
 import * as crypto from 'crypto';
 
 @Injectable()
@@ -20,7 +22,9 @@ export class ExecuteTaskUseCase {
     private readonly engineRegistry: EngineRegistry,
     private readonly sessionRepository: SessionRepository,
     private readonly taskRepository: TaskRepository,
+    private readonly usageRecordRepository: UsageRecordRepository,
     private readonly gateway: AgentStreamGateway,
+    private readonly eventPublisher: EventPublisherPort,
   ) {}
 
   async execute(
@@ -55,7 +59,7 @@ export class ExecuteTaskUseCase {
     await this.taskRepository.save(task);
 
     // Fire-and-forget: iterate engine stream and emit events via gateway
-    this.runEngineStream(engine, session, task, dto);
+    this.runEngineStream(engine, session, task, dto, tenantId);
 
     return { sessionId: session.id, taskId: task.id };
   }
@@ -77,6 +81,7 @@ export class ExecuteTaskUseCase {
     session: AgentSession,
     task: AgentTask,
     dto: ExecuteTaskDto,
+    tenantId: string,
   ): Promise<void> {
     try {
       const stream = engine.executeTask({
@@ -102,6 +107,9 @@ export class ExecuteTaskUseCase {
           session.status = 'completed';
           session.updatedAt = new Date();
           await this.sessionRepository.save(session);
+
+          // Record usage for billing
+          await this.recordUsage(tenantId, task, session, event, engine.engineType);
         }
 
         if (event.type === 'error') {
@@ -141,4 +149,49 @@ export class ExecuteTaskUseCase {
       });
     }
   }
+
+  private async recordUsage(
+    tenantId: string,
+    task: AgentTask,
+    session: AgentSession,
+    event: Extract<EngineStreamEvent, { type: 'completed' }>,
+    engineType: string,
+  ): Promise<void> {
+    const inputTokens = event.inputTokens ?? 0;
+    const outputTokens = event.outputTokens ?? 0;
+    const totalTokens = event.tokensUsed ?? (inputTokens + outputTokens);
+
+    if (totalTokens === 0) return;
+
+    try {
+      const record = new UsageRecord();
+      record.id = crypto.randomUUID();
+      record.tenantId = tenantId;
+      record.taskId = task.id;
+      record.sessionId = session.id;
+      record.engineType = engineType;
+      record.inputTokens = inputTokens;
+      record.outputTokens = outputTokens;
+      record.totalTokens = totalTokens;
+      record.costUsd = event.costUsd ?? 0;
+      record.model = event.model ?? '';
+
+      await this.usageRecordRepository.save(record);
+
+      // Publish billing event for billing-service to aggregate
+      await this.eventPublisher.publish(EventPatterns.USAGE_RECORDED, {
+        tenantId,
+        taskId: task.id,
+        sessionId: session.id,
+        engineType,
+        inputTokens,
+        outputTokens,
+        totalTokens,
+        costUsd: event.costUsd ?? 0,
+        model: event.model ?? '',
+      });
+    } catch (err: any) {
+      this.logger.error(`Failed to record usage for task ${task.id}: ${err.message}`);
+    }
+  }
 }
diff --git a/packages/services/agent-service/src/domain/entities/usage-record.entity.ts b/packages/services/agent-service/src/domain/entities/usage-record.entity.ts
new file mode 100644
index 0000000..44678e2
--- /dev/null
+++ b/packages/services/agent-service/src/domain/entities/usage-record.entity.ts
@@ -0,0 +1,37 @@
+import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn } from 'typeorm';
+
+@Entity('usage_records')
+export class UsageRecord {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ type: 'varchar', length: 20 })
+  tenantId!: string;
+
+  @Column({ type: 'uuid' })
+  taskId!: string;
+
+  @Column({ type: 'uuid' })
+  sessionId!: string;
+
+  @Column({ type: 'varchar', length: 30 })
+  engineType!: string;
+
+  @Column({ type: 'int', default: 0 })
+  inputTokens!: number;
+
+  @Column({ type: 'int', default: 0 })
+  outputTokens!: number;
+
+  @Column({ type: 'int', default: 0 })
+  totalTokens!: number;
+
+  @Column({ type: 'numeric', precision: 10, scale: 6, default: 0 })
+  costUsd!: number;
+
+  @Column({ type: 'varchar', length: 100, default: '' })
+  model!: string;
+
+  @CreateDateColumn({ type: 'timestamptz' })
+  recordedAt!: Date;
+}
diff --git a/packages/services/agent-service/src/domain/ports/outbound/agent-engine.port.ts b/packages/services/agent-service/src/domain/ports/outbound/agent-engine.port.ts
index 0bbc294..0772c57 100644
--- a/packages/services/agent-service/src/domain/ports/outbound/agent-engine.port.ts
+++ b/packages/services/agent-service/src/domain/ports/outbound/agent-engine.port.ts
@@ -36,7 +36,15 @@ export type EngineStreamEvent =
   | { type: 'tool_use'; toolName: string; input: Record<string, unknown> }
   | { type: 'tool_result'; toolName: string; output: string; isError: boolean }
   | { type: 'approval_required'; command: string; riskLevel: number; taskId: string }
-  | { type: 'completed'; summary: string; tokensUsed?: number }
+  | {
+      type: 'completed';
+      summary: string;
+      tokensUsed?: number;
+      inputTokens?: number;
+      outputTokens?: number;
+      costUsd?: number;
+      model?: string;
+    }
   | { type: 'error'; message: string; code: string }
   | { type: 'cancelled'; message: string; code: string }
   | { type: 'task_info'; taskId: string };
diff --git a/packages/services/agent-service/src/infrastructure/engines/claude-agent-sdk/claude-agent-sdk-engine.ts b/packages/services/agent-service/src/infrastructure/engines/claude-agent-sdk/claude-agent-sdk-engine.ts
index 6c6b060..594e8da 100644
--- a/packages/services/agent-service/src/infrastructure/engines/claude-agent-sdk/claude-agent-sdk-engine.ts
+++ b/packages/services/agent-service/src/infrastructure/engines/claude-agent-sdk/claude-agent-sdk-engine.ts
@@ -578,12 +578,20 @@ export class ClaudeAgentSdkEngine implements AgentEnginePort {
         }
       }
     } else if (message.type === 'result') {
+      const inputTokens = message.usage?.input_tokens ?? 0;
+      const outputTokens = message.usage?.output_tokens ?? 0;
+      const totalTokens = inputTokens + outputTokens;
+      const costUsd = message.total_cost_usd != null
+        ? Number(message.total_cost_usd)
+        : (inputTokens * 3 + outputTokens * 15) / 1_000_000;
       events.push({
         type: 'completed',
         summary: message.result ?? '',
-        tokensUsed: message.usage
-          ? (message.usage.input_tokens ?? 0) + (message.usage.output_tokens ?? 0)
-          : undefined,
+        tokensUsed: totalTokens || undefined,
+        inputTokens: inputTokens || undefined,
+        outputTokens: outputTokens || undefined,
+        costUsd: costUsd || undefined,
+        model: message.model ?? 'claude-sonnet-4-5-20250929',
       });
     } else if (message.type === 'system' && message.subtype === 'init') {
       this.logger.log(`SDK session initialized: ${message.session_id}`);
diff --git a/packages/services/agent-service/src/infrastructure/engines/claude-api/claude-api-engine.ts b/packages/services/agent-service/src/infrastructure/engines/claude-api/claude-api-engine.ts
index ef492c8..c8d285e 100644
--- a/packages/services/agent-service/src/infrastructure/engines/claude-api/claude-api-engine.ts
+++ b/packages/services/agent-service/src/infrastructure/engines/claude-api/claude-api-engine.ts
@@ -68,8 +68,10 @@ export class ClaudeApiEngine implements AgentEnginePort {
       ? [...history]
       : [...history, { role: 'user', content: params.prompt }];
 
-    let totalTokensUsed = 0;
+    let totalInputTokens = 0;
+    let totalOutputTokens = 0;
     let turnCount = 0;
+    const engineModel = 'claude-sonnet-4-5-20250929';
 
     try {
       // Agent loop: continue until end_turn or max turns reached
@@ -87,7 +89,7 @@ export class ClaudeApiEngine implements AgentEnginePort {
         }
 
         const requestParams: any = {
-          model: 'claude-sonnet-4-5-20250929',
+          model: engineModel,
           max_tokens: 8192,
           messages,
         };
@@ -130,9 +132,10 @@ export class ClaudeApiEngine implements AgentEnginePort {
         // Get final message for tool use and usage
         const response = await stream.finalMessage();
 
-        // Track token usage
+        // Track token usage (input/output separate for billing)
         if (response.usage) {
-          totalTokensUsed += (response.usage.input_tokens ?? 0) + (response.usage.output_tokens ?? 0);
+          totalInputTokens += response.usage.input_tokens ?? 0;
+          totalOutputTokens += response.usage.output_tokens ?? 0;
         }
 
         // Collect tool_use blocks from final response
@@ -158,10 +161,17 @@ export class ClaudeApiEngine implements AgentEnginePort {
           );
           const summary = (summaryBlock as any)?.text ?? 'Task completed';
 
+          const totalTokens = totalInputTokens + totalOutputTokens;
+          // claude-sonnet-4-5: $3/MTok input, $15/MTok output
+          const costUsd = (totalInputTokens * 3 + totalOutputTokens * 15) / 1_000_000;
           yield {
             type: 'completed' as const,
             summary,
-            tokensUsed: totalTokensUsed,
+            tokensUsed: totalTokens,
+            inputTokens: totalInputTokens,
+            outputTokens: totalOutputTokens,
+            costUsd,
+            model: engineModel,
           };
           return;
         }
@@ -203,10 +213,16 @@ export class ClaudeApiEngine implements AgentEnginePort {
       }
 
       // Max turns reached
+      const totalTokens = totalInputTokens + totalOutputTokens;
+      const costUsd = (totalInputTokens * 3 + totalOutputTokens * 15) / 1_000_000;
       yield {
         type: 'completed',
         summary: `Agent loop completed after reaching max turns (${params.maxTurns})`,
-        tokensUsed: totalTokensUsed,
+        tokensUsed: totalTokens,
+        inputTokens: totalInputTokens,
+        outputTokens: totalOutputTokens,
+        costUsd,
+        model: engineModel,
       };
     } catch (error: any) {
       if (error.name === 'AbortError' || abortController.signal.aborted) {
diff --git a/packages/services/agent-service/src/infrastructure/engines/claude-code-cli/claude-code-engine.ts b/packages/services/agent-service/src/infrastructure/engines/claude-code-cli/claude-code-engine.ts
index efb3f10..65848a6 100644
--- a/packages/services/agent-service/src/infrastructure/engines/claude-code-cli/claude-code-engine.ts
+++ b/packages/services/agent-service/src/infrastructure/engines/claude-code-cli/claude-code-engine.ts
@@ -279,12 +279,21 @@ export class ClaudeCodeCliEngine implements AgentEnginePort {
         isError: parsed.is_error ?? false,
       });
     } else if (parsed.type === 'result') {
+      const inputTokens = parsed.usage?.input_tokens ?? 0;
+      const outputTokens = parsed.usage?.output_tokens ?? 0;
+      const totalTokens = inputTokens + outputTokens;
+      // Use reported cost if available, otherwise estimate at claude-sonnet-4-5 pricing
+      const costUsd = parsed.total_cost_usd != null
+        ? Number(parsed.total_cost_usd)
+        : (inputTokens * 3 + outputTokens * 15) / 1_000_000;
       events.push({
         type: 'completed',
         summary: parsed.result ?? parsed.text ?? 'Task completed',
-        tokensUsed: parsed.total_cost_usd !== undefined
-          ? undefined
-          : (parsed.usage?.input_tokens ?? 0) + (parsed.usage?.output_tokens ?? 0) || undefined,
+        tokensUsed: totalTokens || undefined,
+        inputTokens: inputTokens || undefined,
+        outputTokens: outputTokens || undefined,
+        costUsd: costUsd || undefined,
+        model: parsed.model ?? 'claude-sonnet-4-5-20250929',
       });
     } else if (parsed.type === 'error') {
       events.push({
diff --git a/packages/services/agent-service/src/infrastructure/repositories/usage-record.repository.ts b/packages/services/agent-service/src/infrastructure/repositories/usage-record.repository.ts
new file mode 100644
index 0000000..3299961
--- /dev/null
+++ b/packages/services/agent-service/src/infrastructure/repositories/usage-record.repository.ts
@@ -0,0 +1,24 @@
+import { Injectable } from '@nestjs/common';
+import { DataSource } from 'typeorm';
+import { TenantAwareRepository } from '@it0/database';
+import { UsageRecord } from '../../domain/entities/usage-record.entity';
+
+@Injectable()
+export class UsageRecordRepository extends TenantAwareRepository<UsageRecord> {
+  constructor(dataSource: DataSource) {
+    super(dataSource, UsageRecord);
+  }
+
+  async sumMonthTokens(year: number, month: number): Promise<number> {
+    return this.withRepository(async (repo) => {
+      const start = new Date(year, month - 1, 1);
+      const end = new Date(year, month, 1);
+      const result = await repo
+        .createQueryBuilder('ur')
+        .select('COALESCE(SUM(ur.total_tokens), 0)', 'total')
+        .where('ur.recorded_at >= :start AND ur.recorded_at < :end', { start, end })
+        .getRawOne();
+      return Number(result?.total ?? 0);
+    });
+  }
+}
diff --git a/packages/services/agent-service/src/interfaces/rest/controllers/agent.controller.ts b/packages/services/agent-service/src/interfaces/rest/controllers/agent.controller.ts
index aa6a5eb..bffce03 100644
--- a/packages/services/agent-service/src/interfaces/rest/controllers/agent.controller.ts
+++ b/packages/services/agent-service/src/interfaces/rest/controllers/agent.controller.ts
@@ -1,15 +1,18 @@
 import { Controller, Post, Body, Param, Delete, Get, NotFoundException, BadRequestException, ForbiddenException, Logger } from '@nestjs/common';
-import { TenantId } from '@it0/common';
+import { TenantId, EventPatterns } from '@it0/common';
 import { EngineRegistry } from '../../../infrastructure/engines/engine-registry';
 import { AgentStreamGateway } from '../../ws/agent-stream.gateway';
 import { SessionRepository } from '../../../infrastructure/repositories/session.repository';
 import { TaskRepository } from '../../../infrastructure/repositories/task.repository';
+import { UsageRecordRepository } from '../../../infrastructure/repositories/usage-record.repository';
 import { ConversationContextService } from '../../../domain/services/conversation-context.service';
+import { EventPublisherService } from '../../../infrastructure/messaging/event-publisher.service';
 import { AgentSession } from '../../../domain/entities/agent-session.entity';
 import { AgentTask } from '../../../domain/entities/agent-task.entity';
+import { UsageRecord } from '../../../domain/entities/usage-record.entity';
 import { TaskStatus } from '../../../domain/value-objects/task-status.vo';
 import { AgentEngineType } from '../../../domain/value-objects/agent-engine-type.vo';
-import { AgentEnginePort } from '../../../domain/ports/outbound/agent-engine.port';
+import { AgentEnginePort, EngineStreamEvent } from '../../../domain/ports/outbound/agent-engine.port';
 import { ClaudeAgentSdkEngine } from '../../../infrastructure/engines/claude-agent-sdk/claude-agent-sdk-engine';
 import * as crypto from 'crypto';
 
@@ -24,7 +27,9 @@ export class AgentController {
     private readonly gateway: AgentStreamGateway,
     private readonly sessionRepository: SessionRepository,
     private readonly taskRepository: TaskRepository,
+    private readonly usageRecordRepository: UsageRecordRepository,
     private readonly contextService: ConversationContextService,
+    private readonly eventPublisher: EventPublisherService,
   ) {}
 
   @Post('tasks')
@@ -475,6 +480,11 @@ export class AgentController {
             // Keep session active so it can be reused (also persists captured SDK session ID)
             session.updatedAt = new Date();
             await this.sessionRepository.save(session);
+
+            // Record usage for billing (non-blocking)
+            this.recordUsage(session.tenantId, task, session, event, engine.engineType).catch(
+              (err) => this.logger.error(`[Task ${task.id}] Usage recording failed: ${err.message}`),
+            );
           }
 
           if (event.type === 'error' && !finished) {
@@ -570,6 +580,45 @@ export class AgentController {
     }
   }
 
+  private async recordUsage(
+    tenantId: string,
+    task: AgentTask,
+    session: AgentSession,
+    event: Extract<EngineStreamEvent, { type: 'completed' }>,
+    engineType: string,
+  ): Promise<void> {
+    const inputTokens = event.inputTokens ?? 0;
+    const outputTokens = event.outputTokens ?? 0;
+    const totalTokens = event.tokensUsed ?? (inputTokens + outputTokens);
+    if (totalTokens === 0) return;
+
+    const record = new UsageRecord();
+    record.id = crypto.randomUUID();
+    record.tenantId = tenantId;
+    record.taskId = task.id;
+    record.sessionId = session.id;
+    record.engineType = engineType;
+    record.inputTokens = inputTokens;
+    record.outputTokens = outputTokens;
+    record.totalTokens = totalTokens;
+    record.costUsd = event.costUsd ?? 0;
+    record.model = event.model ?? '';
+
+    await this.usageRecordRepository.save(record);
+
+    await this.eventPublisher.publish(EventPatterns.USAGE_RECORDED, {
+      tenantId,
+      taskId: task.id,
+      sessionId: session.id,
+      engineType,
+      inputTokens,
+      outputTokens,
+      totalTokens,
+      costUsd: event.costUsd ?? 0,
+      model: event.model ?? '',
+    });
+  }
+
   private createNewSession(tenantId: string, engineType: string, systemPrompt?: string): AgentSession {
     const session = new AgentSession();
     session.id = crypto.randomUUID();
diff --git a/packages/services/auth-service/src/application/services/auth.service.ts b/packages/services/auth-service/src/application/services/auth.service.ts
index 7755326..0ccf481 100644
--- a/packages/services/auth-service/src/application/services/auth.service.ts
+++ b/packages/services/auth-service/src/application/services/auth.service.ts
@@ -4,6 +4,8 @@ import {
   ConflictException,
   BadRequestException,
   NotFoundException,
+  HttpException,
+  HttpStatus,
   Logger,
 } from '@nestjs/common';
 import { JwtService } from '@nestjs/jwt';
@@ -235,6 +237,21 @@ export class AuthService {
       throw new NotFoundException('Tenant not found');
     }
 
+    // Check user quota
+    if (tenant.maxUsers !== -1) {
+      const schemaName = `it0_t_${tenantId}`;
+      const countResult = await this.dataSource.query(
+        `SELECT COUNT(*) AS cnt FROM "${schemaName}".users WHERE is_active = true`,
+      );
+      const currentCount = Number(countResult[0]?.cnt ?? 0);
+      if (currentCount >= tenant.maxUsers) {
+        throw new HttpException(
+          { message: `User quota exceeded (${currentCount}/${tenant.maxUsers}). Upgrade your plan to invite more users.`, code: 'QUOTA_EXCEEDED' },
+          HttpStatus.TOO_MANY_REQUESTS,
+        );
+      }
+    }
+
     // Check for existing pending invite
     const existing = await this.inviteRepository.findOne({
       where: { tenantId, email, status: 'pending' as const },
diff --git a/packages/services/billing-service/package.json b/packages/services/billing-service/package.json
new file mode 100644
index 0000000..3b3974b
--- /dev/null
+++ b/packages/services/billing-service/package.json
@@ -0,0 +1,34 @@
+{
+  "name": "@it0/billing-service",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "build": "nest build",
+    "dev": "nest start --watch",
+    "start": "node dist/main",
+    "test": "jest"
+  },
+  "dependencies": {
+    "@nestjs/common": "^10.3.0",
+    "@nestjs/core": "^10.3.0",
+    "@nestjs/config": "^3.2.0",
+    "@nestjs/typeorm": "^10.0.0",
+    "@nestjs/platform-express": "^10.3.0",
+    "@nestjs/schedule": "^4.0.0",
+    "typeorm": "^0.3.20",
+    "pg": "^8.11.0",
+    "reflect-metadata": "^0.2.0",
+    "rxjs": "^7.8.0",
+    "stripe": "^14.0.0",
+    "alipay-sdk": "^4.0.0",
+    "coinbase-commerce-node": "^1.0.4",
+    "@it0/common": "workspace:*",
+    "@it0/database": "workspace:*",
+    "@it0/events": "workspace:*"
+  },
+  "devDependencies": {
+    "@nestjs/cli": "^10.3.0",
+    "@types/node": "^20.11.0",
+    "typescript": "^5.4.0"
+  }
+}
diff --git a/packages/services/billing-service/src/application/use-cases/aggregate-usage.use-case.ts b/packages/services/billing-service/src/application/use-cases/aggregate-usage.use-case.ts
new file mode 100644
index 0000000..fdfa166
--- /dev/null
+++ b/packages/services/billing-service/src/application/use-cases/aggregate-usage.use-case.ts
@@ -0,0 +1,103 @@
+import { Injectable, Logger, OnModuleInit, OnModuleDestroy } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import { createClient, RedisClientType } from 'redis';
+import { UsageAggregateRepository } from '../../infrastructure/repositories/usage-aggregate.repository';
+
+interface UsageRecordedEvent {
+  tenantId: string;
+  taskId: string;
+  inputTokens: number;
+  outputTokens: number;
+  totalTokens: number;
+  costUsd: number;
+  model: string;
+  recordedAt: string;
+}
+
+const STREAM_KEY = 'events:usage.recorded';
+const CONSUMER_GROUP = 'billing-service';
+const CONSUMER_NAME = 'billing-consumer-1';
+
+@Injectable()
+export class AggregateUsageUseCase implements OnModuleInit, OnModuleDestroy {
+  private readonly logger = new Logger(AggregateUsageUseCase.name);
+  private client: RedisClientType;
+  private running = false;
+
+  constructor(
+    private readonly usageAggRepo: UsageAggregateRepository,
+    private readonly configService: ConfigService,
+  ) {}
+
+  async onModuleInit() {
+    const redisUrl = this.configService.get<string>('REDIS_URL', 'redis://localhost:6379');
+    this.client = createClient({ url: redisUrl }) as RedisClientType;
+    await this.client.connect();
+
+    // Create consumer group (ignore error if already exists)
+    try {
+      await this.client.xGroupCreate(STREAM_KEY, CONSUMER_GROUP, '0', { MKSTREAM: true });
+    } catch {
+      // Group already exists
+    }
+
+    this.running = true;
+    this.consumeLoop().catch((err) =>
+      this.logger.error(`Usage consumer loop error: ${err.message}`),
+    );
+  }
+
+  async onModuleDestroy() {
+    this.running = false;
+    await this.client.quit();
+  }
+
+  private async consumeLoop() {
+    while (this.running) {
+      try {
+        const response = await (this.client as any).xReadGroup(
+          CONSUMER_GROUP,
+          CONSUMER_NAME,
+          [{ key: STREAM_KEY, id: '>' }],
+          { COUNT: 10, BLOCK: 5000 },
+        );
+
+        if (!response) continue;
+
+        for (const stream of response) {
+          for (const message of stream.messages) {
+            await this.processMessage(message);
+            await this.client.xAck(STREAM_KEY, CONSUMER_GROUP, message.id);
+          }
+        }
+      } catch (err) {
+        if (this.running) {
+          this.logger.error(`Redis consumer error: ${err.message}`);
+          await new Promise((r) => setTimeout(r, 5000));
+        }
+      }
+    }
+  }
+
+  private async processMessage(message: { id: string; message: Record<string, string> }) {
+    try {
+      const payload: UsageRecordedEvent = JSON.parse(message.message.data ?? '{}');
+      if (!payload.tenantId || !payload.inputTokens) return;
+
+      const recordedAt = new Date(payload.recordedAt ?? Date.now());
+      const year = recordedAt.getFullYear();
+      const month = recordedAt.getMonth() + 1;
+
+      await this.usageAggRepo.upsertTokens(
+        payload.tenantId,
+        year,
+        month,
+        payload.inputTokens ?? 0,
+        payload.outputTokens ?? 0,
+        payload.costUsd ?? 0,
+      );
+    } catch (err) {
+      this.logger.error(`Failed to process usage message ${message.id}: ${err.message}`);
+    }
+  }
+}
diff --git a/packages/services/billing-service/src/application/use-cases/cancel-subscription.use-case.ts b/packages/services/billing-service/src/application/use-cases/cancel-subscription.use-case.ts
new file mode 100644
index 0000000..0c4f61d
--- /dev/null
+++ b/packages/services/billing-service/src/application/use-cases/cancel-subscription.use-case.ts
@@ -0,0 +1,30 @@
+import { Injectable, Logger, NotFoundException } from '@nestjs/common';
+import { SubscriptionRepository } from '../../infrastructure/repositories/subscription.repository';
+import { SubscriptionLifecycleService } from '../../domain/services/subscription-lifecycle.service';
+
+@Injectable()
+export class CancelSubscriptionUseCase {
+  private readonly logger = new Logger(CancelSubscriptionUseCase.name);
+
+  constructor(
+    private readonly subscriptionRepo: SubscriptionRepository,
+    private readonly lifecycle: SubscriptionLifecycleService,
+  ) {}
+
+  /**
+   * @param immediate true = cancel now, false = cancel at period end
+   */
+  async execute(tenantId: string, immediate = false): Promise<void> {
+    const subscription = await this.subscriptionRepo.findByTenantId(tenantId);
+    if (!subscription) throw new NotFoundException(`No subscription found for tenant ${tenantId}`);
+
+    const updated = this.lifecycle.cancel(subscription, immediate);
+    await this.subscriptionRepo.save(updated);
+
+    if (immediate) {
+      this.logger.log(`Tenant ${tenantId} subscription cancelled immediately`);
+    } else {
+      this.logger.log(`Tenant ${tenantId} subscription set to cancel at period end`);
+    }
+  }
+}
diff --git a/packages/services/billing-service/src/application/use-cases/change-plan.use-case.ts b/packages/services/billing-service/src/application/use-cases/change-plan.use-case.ts
new file mode 100644
index 0000000..6c34b11
--- /dev/null
+++ b/packages/services/billing-service/src/application/use-cases/change-plan.use-case.ts
@@ -0,0 +1,86 @@
+import { Injectable, Logger, NotFoundException, BadRequestException } from '@nestjs/common';
+import { PlanRepository } from '../../infrastructure/repositories/plan.repository';
+import { SubscriptionRepository } from '../../infrastructure/repositories/subscription.repository';
+import { InvoiceRepository } from '../../infrastructure/repositories/invoice.repository';
+import { SubscriptionLifecycleService } from '../../domain/services/subscription-lifecycle.service';
+import { InvoiceGeneratorService } from '../../domain/services/invoice-generator.service';
+import { InvoiceCurrency } from '../../domain/entities/invoice.entity';
+
+export interface ChangePlanDto {
+  tenantId: string;
+  newPlanName: string;
+  currency?: InvoiceCurrency;
+}
+
+@Injectable()
+export class ChangePlanUseCase {
+  private readonly logger = new Logger(ChangePlanUseCase.name);
+
+  constructor(
+    private readonly planRepo: PlanRepository,
+    private readonly subscriptionRepo: SubscriptionRepository,
+    private readonly invoiceRepo: InvoiceRepository,
+    private readonly lifecycle: SubscriptionLifecycleService,
+    private readonly invoiceGenerator: InvoiceGeneratorService,
+  ) {}
+
+  async execute(dto: ChangePlanDto): Promise<void> {
+    const { tenantId, newPlanName, currency = InvoiceCurrency.USD } = dto;
+
+    const subscription = await this.subscriptionRepo.findByTenantId(tenantId);
+    if (!subscription) throw new NotFoundException(`No subscription found for tenant ${tenantId}`);
+
+    const currentPlan = await this.planRepo.findById(subscription.planId);
+    if (!currentPlan) throw new NotFoundException('Current plan not found');
+
+    const newPlan = await this.planRepo.findByName(newPlanName);
+    if (!newPlan) throw new NotFoundException(`Plan '${newPlanName}' not found`);
+
+    if (currentPlan.id === newPlan.id) {
+      throw new BadRequestException('Already on this plan');
+    }
+
+    const isUpgrade = newPlan.monthlyPriceUsdCents > currentPlan.monthlyPriceUsdCents;
+
+    if (isUpgrade) {
+      // Immediate upgrade with proration invoice item
+      const updated = this.lifecycle.upgradeNow(subscription, newPlan.id);
+      await this.subscriptionRepo.save(updated);
+
+      // Generate proration charge if not on free plan
+      if (newPlan.monthlyPriceUsdCents > 0 && currentPlan.monthlyPriceUsdCents >= 0) {
+        const invoiceNumber = await this.invoiceRepo.getNextInvoiceNumber();
+        const proratedItem = this.invoiceGenerator.generateProratedUpgradeItem(
+          currentPlan,
+          newPlan,
+          new Date(),
+          subscription.currentPeriodEnd,
+          currency,
+        );
+        if (proratedItem.amount > 0) {
+          const proInvoice = {
+            tenantId,
+            subscriptionId: subscription.id,
+            invoiceNumber,
+            currency,
+            periodStart: new Date(),
+            periodEnd: subscription.currentPeriodEnd,
+            dueDate: new Date(),
+            subtotalCents: proratedItem.amount,
+            taxCents: 0,
+            totalCents: proratedItem.amount,
+            amountDueCents: proratedItem.amount,
+          } as any;
+          await this.invoiceRepo.saveWithItems(proInvoice, [proratedItem]);
+        }
+      }
+
+      this.logger.log(`Tenant ${tenantId} upgraded to ${newPlanName}`);
+    } else {
+      // Downgrade: schedule for next period
+      const updated = this.lifecycle.scheduleDowngrade(subscription, newPlan.id);
+      await this.subscriptionRepo.save(updated);
+      this.logger.log(`Tenant ${tenantId} scheduled downgrade to ${newPlanName} at period end`);
+    }
+  }
+}
diff --git a/packages/services/billing-service/src/application/use-cases/check-token-quota.use-case.ts b/packages/services/billing-service/src/application/use-cases/check-token-quota.use-case.ts
new file mode 100644
index 0000000..33df31c
--- /dev/null
+++ b/packages/services/billing-service/src/application/use-cases/check-token-quota.use-case.ts
@@ -0,0 +1,82 @@
+import { Injectable } from '@nestjs/common';
+import { PlanRepository } from '../../infrastructure/repositories/plan.repository';
+import { SubscriptionRepository } from '../../infrastructure/repositories/subscription.repository';
+import { UsageAggregateRepository } from '../../infrastructure/repositories/usage-aggregate.repository';
+
+export interface QuotaCheckResult {
+  allowed: boolean;
+  remaining: number;
+  usedTokens: number;
+  limitTokens: number;
+  isHardLimit: boolean;
+  overageAllowed: boolean;
+}
+
+@Injectable()
+export class CheckTokenQuotaUseCase {
+  constructor(
+    private readonly planRepo: PlanRepository,
+    private readonly subscriptionRepo: SubscriptionRepository,
+    private readonly usageAggRepo: UsageAggregateRepository,
+  ) {}
+
+  async execute(tenantId: string): Promise<QuotaCheckResult> {
+    const subscription = await this.subscriptionRepo.findByTenantId(tenantId);
+    if (!subscription) {
+      // No subscription: block all usage
+      return { allowed: false, remaining: 0, usedTokens: 0, limitTokens: 0, isHardLimit: true, overageAllowed: false };
+    }
+
+    const plan = await this.planRepo.findById(subscription.planId);
+    if (!plan) {
+      return { allowed: false, remaining: 0, usedTokens: 0, limitTokens: 0, isHardLimit: true, overageAllowed: false };
+    }
+
+    const now = new Date();
+    const usage = await this.usageAggRepo.findByTenantAndPeriod(
+      tenantId,
+      now.getFullYear(),
+      now.getMonth() + 1,
+    );
+
+    const usedTokens = usage?.totalTokens ?? 0;
+    const baseLimit = plan.includedTokensPerMonth;
+
+    // Enterprise: no limit (-1)
+    if (baseLimit === -1) {
+      return {
+        allowed: true,
+        remaining: Number.MAX_SAFE_INTEGER,
+        usedTokens,
+        limitTokens: -1,
+        isHardLimit: false,
+        overageAllowed: true,
+      };
+    }
+
+    const hardLimitTokens = Math.floor(baseLimit * (plan.hardLimitPercent / 100));
+    const overageAllowed = plan.overageRateCentsPerMToken > 0;
+
+    // Hard limit check (applies to all plans)
+    if (plan.hardLimitPercent > 0 && usedTokens >= hardLimitTokens) {
+      return {
+        allowed: false,
+        remaining: 0,
+        usedTokens,
+        limitTokens: hardLimitTokens,
+        isHardLimit: true,
+        overageAllowed,
+      };
+    }
+
+    const remaining = hardLimitTokens - usedTokens;
+    return {
+      allowed: true,
+      remaining,
+      usedTokens,
+      limitTokens: hardLimitTokens,
+      isHardLimit: false,
+      overageAllowed,
+    };
+  }
+}
diff --git a/packages/services/billing-service/src/application/use-cases/create-payment-session.use-case.ts b/packages/services/billing-service/src/application/use-cases/create-payment-session.use-case.ts
new file mode 100644
index 0000000..69ddc05
--- /dev/null
+++ b/packages/services/billing-service/src/application/use-cases/create-payment-session.use-case.ts
@@ -0,0 +1,66 @@
+import { Injectable, NotFoundException, BadRequestException } from '@nestjs/common';
+import { PaymentProviderRegistry } from '../../infrastructure/payment-providers/payment-provider.registry';
+import { PaymentRepository } from '../../infrastructure/repositories/payment.repository';
+import { InvoiceRepository } from '../../infrastructure/repositories/invoice.repository';
+import { SubscriptionRepository } from '../../infrastructure/repositories/subscription.repository';
+import { Payment, PaymentStatus } from '../../domain/entities/payment.entity';
+import { PaymentProviderType } from '../../domain/ports/payment-provider.port';
+import { InvoiceStatus } from '../../domain/entities/invoice.entity';
+
+export interface CreatePaymentSessionDto {
+  tenantId: string;
+  invoiceId: string;
+  provider: PaymentProviderType;
+  returnUrl?: string;
+}
+
+@Injectable()
+export class CreatePaymentSessionUseCase {
+  constructor(
+    private readonly providerRegistry: PaymentProviderRegistry,
+    private readonly paymentRepo: PaymentRepository,
+    private readonly invoiceRepo: InvoiceRepository,
+    private readonly subscriptionRepo: SubscriptionRepository,
+  ) {}
+
+  async execute(dto: CreatePaymentSessionDto) {
+    const { tenantId, invoiceId, provider, returnUrl } = dto;
+
+    const invoice = await this.invoiceRepo.findById(invoiceId);
+    if (!invoice || invoice.tenantId !== tenantId) {
+      throw new NotFoundException('Invoice not found');
+    }
+    if (invoice.status === InvoiceStatus.PAID) {
+      throw new BadRequestException('Invoice is already paid');
+    }
+
+    const paymentProvider = this.providerRegistry.get(provider);
+    if (!paymentProvider) {
+      throw new BadRequestException(`Payment provider '${provider}' is not configured`);
+    }
+
+    const session = await paymentProvider.createPaymentSession({
+      invoiceId,
+      tenantId,
+      amountCents: invoice.amountDueCents,
+      currency: invoice.currency,
+      description: `IT0 Invoice ${invoice.invoiceNumber}`,
+      returnUrl,
+    });
+
+    // Create a pending payment record
+    const payment = new Payment();
+    payment.tenantId = tenantId;
+    payment.invoiceId = invoiceId;
+    payment.provider = provider;
+    payment.providerPaymentId = session.providerPaymentId;
+    payment.amountCents = invoice.amountDueCents;
+    payment.currency = invoice.currency;
+    payment.status = PaymentStatus.PENDING;
+    payment.metadata = { sessionId: session.sessionId };
+
+    await this.paymentRepo.savePayment(payment);
+
+    return session;
+  }
+}
diff --git a/packages/services/billing-service/src/application/use-cases/create-subscription.use-case.ts b/packages/services/billing-service/src/application/use-cases/create-subscription.use-case.ts
new file mode 100644
index 0000000..67f0631
--- /dev/null
+++ b/packages/services/billing-service/src/application/use-cases/create-subscription.use-case.ts
@@ -0,0 +1,34 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { PlanRepository } from '../../infrastructure/repositories/plan.repository';
+import { SubscriptionRepository } from '../../infrastructure/repositories/subscription.repository';
+import { SubscriptionLifecycleService } from '../../domain/services/subscription-lifecycle.service';
+
+@Injectable()
+export class CreateSubscriptionUseCase {
+  private readonly logger = new Logger(CreateSubscriptionUseCase.name);
+
+  constructor(
+    private readonly planRepo: PlanRepository,
+    private readonly subscriptionRepo: SubscriptionRepository,
+    private readonly lifecycle: SubscriptionLifecycleService,
+  ) {}
+
+  async execute(tenantId: string, planName = 'free'): Promise<void> {
+    // Check if subscription already exists
+    const existing = await this.subscriptionRepo.findByTenantId(tenantId);
+    if (existing) {
+      this.logger.warn(`Subscription already exists for tenant ${tenantId}`);
+      return;
+    }
+
+    const plan = await this.planRepo.findByName(planName);
+    if (!plan) {
+      throw new Error(`Plan '${planName}' not found`);
+    }
+
+    const subscription = this.lifecycle.createTrial(tenantId, plan);
+    await this.subscriptionRepo.save(subscription);
+
+    this.logger.log(`Created ${planName} trial subscription for tenant ${tenantId}`);
+  }
+}
diff --git a/packages/services/billing-service/src/application/use-cases/generate-monthly-invoice.use-case.ts b/packages/services/billing-service/src/application/use-cases/generate-monthly-invoice.use-case.ts
new file mode 100644
index 0000000..1e69c57
--- /dev/null
+++ b/packages/services/billing-service/src/application/use-cases/generate-monthly-invoice.use-case.ts
@@ -0,0 +1,122 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { InjectDataSource } from '@nestjs/typeorm';
+import { DataSource } from 'typeorm';
+import { PlanRepository } from '../../infrastructure/repositories/plan.repository';
+import { SubscriptionRepository } from '../../infrastructure/repositories/subscription.repository';
+import { InvoiceRepository } from '../../infrastructure/repositories/invoice.repository';
+import { UsageAggregateRepository } from '../../infrastructure/repositories/usage-aggregate.repository';
+import { InvoiceGeneratorService } from '../../domain/services/invoice-generator.service';
+import { SubscriptionLifecycleService } from '../../domain/services/subscription-lifecycle.service';
+import { InvoiceCurrency } from '../../domain/entities/invoice.entity';
+import { SubscriptionStatus } from '../../domain/entities/subscription.entity';
+
+@Injectable()
+export class GenerateMonthlyInvoiceUseCase {
+  private readonly logger = new Logger(GenerateMonthlyInvoiceUseCase.name);
+
+  constructor(
+    private readonly planRepo: PlanRepository,
+    private readonly subscriptionRepo: SubscriptionRepository,
+    private readonly invoiceRepo: InvoiceRepository,
+    private readonly usageAggRepo: UsageAggregateRepository,
+    private readonly invoiceGenerator: InvoiceGeneratorService,
+    private readonly lifecycle: SubscriptionLifecycleService,
+  ) {}
+
+  /**
+   * Called by cron on the 1st of each month.
+   * Generates invoices for the previous month and renews active subscriptions.
+   */
+  async execute(): Promise<void> {
+    const now = new Date();
+    const prevMonth = now.getMonth() === 0 ? 12 : now.getMonth();
+    const prevYear = now.getMonth() === 0 ? now.getFullYear() - 1 : now.getFullYear();
+
+    this.logger.log(`Generating monthly invoices for ${prevYear}-${String(prevMonth).padStart(2, '0')}`);
+
+    // Find all subscriptions that expired (period end passed) or are active with cancelAtPeriodEnd
+    const expired = await this.subscriptionRepo.findExpired();
+    const cancelAtEnd = await this.subscriptionRepo.findCancelAtPeriodEnd();
+
+    // Process expired subscriptions
+    for (const sub of expired) {
+      try {
+        await this.processSubscription(sub, prevYear, prevMonth);
+      } catch (err) {
+        this.logger.error(`Failed to process subscription ${sub.id} for tenant ${sub.tenantId}: ${err.message}`);
+      }
+    }
+
+    // Process cancellations
+    for (const sub of cancelAtEnd) {
+      try {
+        if (sub.currentPeriodEnd <= now) {
+          const updated = this.lifecycle.cancel(sub, true);
+          await this.subscriptionRepo.save(updated);
+          this.logger.log(`Cancelled subscription for tenant ${sub.tenantId} at period end`);
+        }
+      } catch (err) {
+        this.logger.error(`Failed to cancel subscription ${sub.id}: ${err.message}`);
+      }
+    }
+  }
+
+  private async processSubscription(sub: any, year: number, month: number): Promise<void> {
+    const plan = await this.planRepo.findById(sub.planId);
+    if (!plan) {
+      this.logger.warn(`Plan ${sub.planId} not found for subscription ${sub.id}`);
+      return;
+    }
+
+    const usage = await this.usageAggRepo.findByTenantAndPeriod(sub.tenantId, year, month);
+    if (!usage) {
+      this.logger.debug(`No usage data for tenant ${sub.tenantId} in ${year}-${month}`);
+    }
+
+    // Only generate invoice if plan costs money
+    if (plan.monthlyPriceUsdCents > 0 || (usage && usage.totalTokens > plan.includedTokensPerMonth)) {
+      const invoiceNumber = await this.invoiceRepo.getNextInvoiceNumber();
+      const { invoice, items } = this.invoiceGenerator.generateMonthlyInvoice(
+        sub,
+        plan,
+        usage ?? this.emptyUsage(sub.tenantId, year, month),
+        InvoiceCurrency.USD,
+        invoiceNumber,
+      );
+
+      await this.invoiceRepo.saveWithItems(invoice, items);
+      this.logger.log(`Generated invoice ${invoiceNumber} for tenant ${sub.tenantId}`);
+    }
+
+    // Renew the subscription (apply scheduled downgrade if any)
+    if (sub.status === SubscriptionStatus.ACTIVE) {
+      const renewed = this.lifecycle.renew(sub);
+      await this.subscriptionRepo.save(renewed);
+    } else if (sub.status === SubscriptionStatus.TRIALING && sub.trialEndsAt <= new Date()) {
+      // Trial expired: activate if paid plan, else keep on free
+      if (plan.monthlyPriceUsdCents === 0) {
+        const activated = this.lifecycle.activate(sub);
+        await this.subscriptionRepo.save(activated);
+      } else {
+        // Mark as past_due until payment received
+        const pastDue = this.lifecycle.markPastDue(sub);
+        await this.subscriptionRepo.save(pastDue);
+      }
+    }
+  }
+
+  private emptyUsage(tenantId: string, year: number, month: number): any {
+    return {
+      tenantId,
+      year,
+      month,
+      totalInputTokens: 0,
+      totalOutputTokens: 0,
+      totalTokens: 0,
+      totalCostUsd: 0,
+      taskCount: 0,
+      periodStart: new Date(year, month - 1, 1),
+      periodEnd: new Date(year, month, 0, 23, 59, 59),
+    };
+  }
+}
diff --git a/packages/services/billing-service/src/application/use-cases/handle-payment-webhook.use-case.ts b/packages/services/billing-service/src/application/use-cases/handle-payment-webhook.use-case.ts
new file mode 100644
index 0000000..5a62e17
--- /dev/null
+++ b/packages/services/billing-service/src/application/use-cases/handle-payment-webhook.use-case.ts
@@ -0,0 +1,101 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { PaymentRepository } from '../../infrastructure/repositories/payment.repository';
+import { InvoiceRepository } from '../../infrastructure/repositories/invoice.repository';
+import { SubscriptionRepository } from '../../infrastructure/repositories/subscription.repository';
+import { PaymentStatus } from '../../domain/entities/payment.entity';
+import { InvoiceStatus } from '../../domain/entities/invoice.entity';
+import { SubscriptionLifecycleService } from '../../domain/services/subscription-lifecycle.service';
+import { PaymentProviderType, WebhookResult } from '../../domain/ports/payment-provider.port';
+import { PaymentProviderRegistry } from '../../infrastructure/payment-providers/payment-provider.registry';
+
+@Injectable()
+export class HandlePaymentWebhookUseCase {
+  private readonly logger = new Logger(HandlePaymentWebhookUseCase.name);
+
+  constructor(
+    private readonly providerRegistry: PaymentProviderRegistry,
+    private readonly paymentRepo: PaymentRepository,
+    private readonly invoiceRepo: InvoiceRepository,
+    private readonly subscriptionRepo: SubscriptionRepository,
+    private readonly lifecycle: SubscriptionLifecycleService,
+  ) {}
+
+  async execute(provider: PaymentProviderType, rawBody: Buffer, headers: Record<string, string>): Promise<void> {
+    const paymentProvider = this.providerRegistry.get(provider);
+    if (!paymentProvider) {
+      this.logger.warn(`Webhook received for unconfigured provider: ${provider}`);
+      return;
+    }
+
+    let result: WebhookResult;
+    try {
+      result = await paymentProvider.handleWebhook(rawBody, headers);
+    } catch (err) {
+      this.logger.error(`Webhook signature verification failed for ${provider}: ${err.message}`);
+      throw err;
+    }
+
+    if (!result || result.type === 'unknown') return;
+
+    if (result.type === 'payment_succeeded') {
+      await this.handlePaymentSucceeded(result.providerPaymentId, result.metadata);
+    } else if (result.type === 'payment_failed') {
+      await this.handlePaymentFailed(result.providerPaymentId);
+    } else if (result.type === 'refunded') {
+      await this.handleRefund(result.providerPaymentId);
+    }
+  }
+
+  private async handlePaymentSucceeded(providerPaymentId: string, metadata?: Record<string, any>) {
+    const payment = await this.paymentRepo.findByProviderPaymentId(providerPaymentId);
+    if (!payment) {
+      this.logger.warn(`Payment not found for provider ID: ${providerPaymentId}`);
+      return;
+    }
+
+    payment.status = PaymentStatus.SUCCEEDED;
+    payment.paidAt = new Date();
+    await this.paymentRepo.savePayment(payment);
+
+    // Mark invoice as paid
+    const invoice = await this.invoiceRepo.findById(payment.invoiceId);
+    if (invoice) {
+      invoice.status = InvoiceStatus.PAID;
+      invoice.paidAt = new Date();
+      await this.invoiceRepo.save(invoice);
+    }
+
+    // Activate/renew subscription
+    const subscription = await this.subscriptionRepo.findByTenantId(payment.tenantId);
+    if (subscription) {
+      const activated = this.lifecycle.activate(subscription);
+      await this.subscriptionRepo.save(activated);
+      this.logger.log(`Subscription activated for tenant ${payment.tenantId}`);
+    }
+  }
+
+  private async handlePaymentFailed(providerPaymentId: string) {
+    const payment = await this.paymentRepo.findByProviderPaymentId(providerPaymentId);
+    if (!payment) return;
+
+    payment.status = PaymentStatus.FAILED;
+    await this.paymentRepo.savePayment(payment);
+
+    // Mark subscription as past_due
+    const subscription = await this.subscriptionRepo.findByTenantId(payment.tenantId);
+    if (subscription) {
+      const pastDue = this.lifecycle.markPastDue(subscription);
+      await this.subscriptionRepo.save(pastDue);
+      this.logger.warn(`Subscription marked past_due for tenant ${payment.tenantId}`);
+    }
+  }
+
+  private async handleRefund(providerPaymentId: string) {
+    const payment = await this.paymentRepo.findByProviderPaymentId(providerPaymentId);
+    if (!payment) return;
+
+    payment.status = PaymentStatus.REFUNDED;
+    await this.paymentRepo.savePayment(payment);
+    this.logger.log(`Refund processed for payment ${providerPaymentId}`);
+  }
+}
diff --git a/packages/services/billing-service/src/billing.module.ts b/packages/services/billing-service/src/billing.module.ts
new file mode 100644
index 0000000..e45c7e5
--- /dev/null
+++ b/packages/services/billing-service/src/billing.module.ts
@@ -0,0 +1,108 @@
+import { Module } from '@nestjs/common';
+import { ConfigModule } from '@nestjs/config';
+import { TypeOrmModule } from '@nestjs/typeorm';
+import { ScheduleModule } from '@nestjs/schedule';
+import { DatabaseModule } from '@it0/database';
+
+// Domain Entities
+import { Plan } from './domain/entities/plan.entity';
+import { Subscription } from './domain/entities/subscription.entity';
+import { Invoice } from './domain/entities/invoice.entity';
+import { InvoiceItem } from './domain/entities/invoice-item.entity';
+import { Payment } from './domain/entities/payment.entity';
+import { PaymentMethod } from './domain/entities/payment-method.entity';
+import { UsageAggregate } from './domain/entities/usage-aggregate.entity';
+
+// Domain Services
+import { OverageCalculatorService } from './domain/services/overage-calculator.service';
+import { SubscriptionLifecycleService } from './domain/services/subscription-lifecycle.service';
+import { InvoiceGeneratorService } from './domain/services/invoice-generator.service';
+
+// Infrastructure Repositories
+import { PlanRepository } from './infrastructure/repositories/plan.repository';
+import { SubscriptionRepository } from './infrastructure/repositories/subscription.repository';
+import { InvoiceRepository } from './infrastructure/repositories/invoice.repository';
+import { PaymentRepository } from './infrastructure/repositories/payment.repository';
+import { UsageAggregateRepository } from './infrastructure/repositories/usage-aggregate.repository';
+
+// Payment Providers
+import { PaymentProviderRegistry } from './infrastructure/payment-providers/payment-provider.registry';
+import { StripeProvider } from './infrastructure/payment-providers/stripe/stripe.provider';
+import { AlipayProvider } from './infrastructure/payment-providers/alipay/alipay.provider';
+import { WeChatPayProvider } from './infrastructure/payment-providers/wechat/wechat-pay.provider';
+import { CryptoProvider } from './infrastructure/payment-providers/crypto/crypto.provider';
+
+// Application Use Cases
+import { CreateSubscriptionUseCase } from './application/use-cases/create-subscription.use-case';
+import { ChangePlanUseCase } from './application/use-cases/change-plan.use-case';
+import { CancelSubscriptionUseCase } from './application/use-cases/cancel-subscription.use-case';
+import { GenerateMonthlyInvoiceUseCase } from './application/use-cases/generate-monthly-invoice.use-case';
+import { AggregateUsageUseCase } from './application/use-cases/aggregate-usage.use-case';
+import { CheckTokenQuotaUseCase } from './application/use-cases/check-token-quota.use-case';
+import { CreatePaymentSessionUseCase } from './application/use-cases/create-payment-session.use-case';
+import { HandlePaymentWebhookUseCase } from './application/use-cases/handle-payment-webhook.use-case';
+
+// Controllers
+import { PlanController } from './interfaces/rest/controllers/plan.controller';
+import { SubscriptionController } from './interfaces/rest/controllers/subscription.controller';
+import { InvoiceController } from './interfaces/rest/controllers/invoice.controller';
+import { PaymentMethodController } from './interfaces/rest/controllers/payment-method.controller';
+import { WebhookController } from './interfaces/rest/controllers/webhook.controller';
+
+// Cron scheduler
+import { BillingScheduler } from './infrastructure/scheduler/billing.scheduler';
+import { PlanSeedService } from './infrastructure/seed/plan-seed.service';
+
+@Module({
+  imports: [
+    ConfigModule.forRoot({ isGlobal: true }),
+    DatabaseModule.forRoot(),
+    TypeOrmModule.forFeature([
+      Plan, Subscription, Invoice, InvoiceItem,
+      Payment, PaymentMethod, UsageAggregate,
+    ]),
+    ScheduleModule.forRoot(),
+  ],
+  controllers: [
+    PlanController,
+    SubscriptionController,
+    InvoiceController,
+    PaymentMethodController,
+    WebhookController,
+  ],
+  providers: [
+    // Domain services
+    OverageCalculatorService,
+    SubscriptionLifecycleService,
+    InvoiceGeneratorService,
+
+    // Repositories
+    PlanRepository,
+    SubscriptionRepository,
+    InvoiceRepository,
+    PaymentRepository,
+    UsageAggregateRepository,
+
+    // Payment providers
+    StripeProvider,
+    AlipayProvider,
+    WeChatPayProvider,
+    CryptoProvider,
+    PaymentProviderRegistry,
+
+    // Use cases
+    CreateSubscriptionUseCase,
+    ChangePlanUseCase,
+    CancelSubscriptionUseCase,
+    GenerateMonthlyInvoiceUseCase,
+    AggregateUsageUseCase,
+    CheckTokenQuotaUseCase,
+    CreatePaymentSessionUseCase,
+    HandlePaymentWebhookUseCase,
+
+    // Scheduler
+    BillingScheduler,
+    PlanSeedService,
+  ],
+})
+export class BillingModule {}
diff --git a/packages/services/billing-service/src/domain/entities/invoice-item.entity.ts b/packages/services/billing-service/src/domain/entities/invoice-item.entity.ts
new file mode 100644
index 0000000..36619e9
--- /dev/null
+++ b/packages/services/billing-service/src/domain/entities/invoice-item.entity.ts
@@ -0,0 +1,25 @@
+import { Entity, PrimaryGeneratedColumn, Column } from 'typeorm';
+
+@Entity({ name: 'invoice_items', schema: 'public' })
+export class InvoiceItem {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ type: 'uuid' })
+  invoiceId!: string;
+
+  @Column({ type: 'varchar', length: 200 })
+  description!: string; // e.g. 'Pro Plan - Monthly', 'Token Overage (2.5M tokens)'
+
+  @Column({ type: 'varchar', length: 30 })
+  itemType!: string; // 'subscription' | 'overage' | 'credit' | 'adjustment'
+
+  @Column({ type: 'numeric', precision: 12, scale: 4 })
+  quantity!: number; // 1 for subscription, 2.5 for 2.5M tokens overage
+
+  @Column({ type: 'int' })
+  unitPrice!: number; // in cents/fen
+
+  @Column({ type: 'int' })
+  amount!: number; // quantity * unitPrice (rounded)
+}
diff --git a/packages/services/billing-service/src/domain/entities/invoice.entity.ts b/packages/services/billing-service/src/domain/entities/invoice.entity.ts
new file mode 100644
index 0000000..13245bf
--- /dev/null
+++ b/packages/services/billing-service/src/domain/entities/invoice.entity.ts
@@ -0,0 +1,48 @@
+import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn } from 'typeorm';
+
+export type InvoiceStatus = 'draft' | 'open' | 'paid' | 'void' | 'uncollectible';
+
+@Entity({ name: 'invoices', schema: 'public' })
+export class Invoice {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ type: 'varchar', length: 100 })
+  tenantId!: string;
+
+  @Column({ type: 'uuid' })
+  subscriptionId!: string;
+
+  @Column({ type: 'varchar', length: 30, unique: true })
+  invoiceNumber!: string; // e.g. INV-2026-03-0001
+
+  @Column({ type: 'varchar', length: 20, default: 'draft' })
+  status!: InvoiceStatus;
+
+  @Column({ type: 'varchar', length: 3 })
+  currency!: string; // 'USD' | 'CNY'
+
+  @Column({ type: 'int', default: 0 })
+  subtotalAmount!: number; // in cents/fen
+
+  @Column({ type: 'int', default: 0 })
+  taxAmount!: number;
+
+  @Column({ type: 'int', default: 0 })
+  totalAmount!: number;
+
+  @Column({ type: 'timestamptz' })
+  periodStart!: Date;
+
+  @Column({ type: 'timestamptz' })
+  periodEnd!: Date;
+
+  @Column({ type: 'timestamptz' })
+  dueDate!: Date;
+
+  @Column({ type: 'timestamptz', nullable: true })
+  paidAt?: Date;
+
+  @CreateDateColumn({ type: 'timestamptz' })
+  createdAt!: Date;
+}
diff --git a/packages/services/billing-service/src/domain/entities/payment-method.entity.ts b/packages/services/billing-service/src/domain/entities/payment-method.entity.ts
new file mode 100644
index 0000000..ce5c8bf
--- /dev/null
+++ b/packages/services/billing-service/src/domain/entities/payment-method.entity.ts
@@ -0,0 +1,28 @@
+import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn } from 'typeorm';
+
+@Entity({ name: 'payment_methods', schema: 'public' })
+export class PaymentMethod {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ type: 'varchar', length: 100 })
+  tenantId!: string;
+
+  @Column({ type: 'varchar', length: 20 })
+  provider!: string; // 'stripe' | 'alipay' | 'wechat_pay' | 'crypto'
+
+  @Column({ type: 'varchar', length: 30 })
+  type!: string; // 'card' | 'alipay_account' | 'wechat_openid' | 'crypto_wallet'
+
+  @Column({ type: 'boolean', default: false })
+  isDefault!: boolean;
+
+  @Column({ type: 'jsonb', default: '{}' })
+  details!: Record<string, any>; // { last4: '4242', brand: 'visa' } — NEVER store full card numbers
+
+  @Column({ type: 'varchar', length: 200, nullable: true })
+  providerCustomerId?: string;
+
+  @CreateDateColumn({ type: 'timestamptz' })
+  createdAt!: Date;
+}
diff --git a/packages/services/billing-service/src/domain/entities/payment.entity.ts b/packages/services/billing-service/src/domain/entities/payment.entity.ts
new file mode 100644
index 0000000..0e26461
--- /dev/null
+++ b/packages/services/billing-service/src/domain/entities/payment.entity.ts
@@ -0,0 +1,39 @@
+import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn, UpdateDateColumn } from 'typeorm';
+
+export type PaymentStatus = 'pending' | 'processing' | 'succeeded' | 'failed' | 'refunded';
+
+@Entity({ name: 'payments', schema: 'public' })
+export class Payment {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ type: 'varchar', length: 100 })
+  tenantId!: string;
+
+  @Column({ type: 'uuid', nullable: true })
+  invoiceId?: string;
+
+  @Column({ type: 'varchar', length: 20 })
+  provider!: string; // 'stripe' | 'alipay' | 'wechat_pay' | 'crypto'
+
+  @Column({ type: 'varchar', length: 200 })
+  providerPaymentId!: string;
+
+  @Column({ type: 'int' })
+  amount!: number; // in cents/fen
+
+  @Column({ type: 'varchar', length: 3 })
+  currency!: string;
+
+  @Column({ type: 'varchar', length: 20, default: 'pending' })
+  status!: PaymentStatus;
+
+  @Column({ type: 'jsonb', default: '{}' })
+  metadata!: Record<string, any>;
+
+  @CreateDateColumn({ type: 'timestamptz' })
+  createdAt!: Date;
+
+  @UpdateDateColumn({ type: 'timestamptz' })
+  updatedAt!: Date;
+}
diff --git a/packages/services/billing-service/src/domain/entities/plan.entity.ts b/packages/services/billing-service/src/domain/entities/plan.entity.ts
new file mode 100644
index 0000000..36d9b96
--- /dev/null
+++ b/packages/services/billing-service/src/domain/entities/plan.entity.ts
@@ -0,0 +1,55 @@
+import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn, UpdateDateColumn } from 'typeorm';
+
+@Entity({ name: 'plans', schema: 'public' })
+export class Plan {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ type: 'varchar', length: 30, unique: true })
+  name!: string; // 'free' | 'pro' | 'enterprise'
+
+  @Column({ type: 'varchar', length: 100 })
+  displayName!: string;
+
+  @Column({ type: 'int', default: 0 })
+  monthlyPriceCentsUsd!: number; // e.g. 4999 = $49.99
+
+  @Column({ type: 'int', default: 0 })
+  monthlyPriceFenCny!: number; // e.g. 34900 = ¥349.00
+
+  @Column({ type: 'bigint', default: 100000 })
+  includedTokens!: number; // tokens per month included in plan
+
+  @Column({ type: 'int', default: 0 })
+  overageRateCentsPerMTokenUsd!: number; // price per 1M overage tokens in cents
+
+  @Column({ type: 'int', default: 5 })
+  maxServers!: number; // -1 = unlimited
+
+  @Column({ type: 'int', default: 3 })
+  maxUsers!: number; // -1 = unlimited
+
+  @Column({ type: 'int', default: 10 })
+  maxStandingOrders!: number; // -1 = unlimited
+
+  @Column({ type: 'int', default: 100 })
+  hardLimitPercent!: number; // 100 = block at 100%, 150 = block at 150%, 0 = no limit
+
+  @Column({ type: 'jsonb', default: '{}' })
+  features!: Record<string, boolean>;
+
+  @Column({ type: 'boolean', default: true })
+  isActive!: boolean;
+
+  @Column({ type: 'int', default: 0 })
+  sortOrder!: number;
+
+  @Column({ type: 'int', default: 14 })
+  trialDays!: number;
+
+  @CreateDateColumn({ type: 'timestamptz' })
+  createdAt!: Date;
+
+  @UpdateDateColumn({ type: 'timestamptz' })
+  updatedAt!: Date;
+}
diff --git a/packages/services/billing-service/src/domain/entities/subscription.entity.ts b/packages/services/billing-service/src/domain/entities/subscription.entity.ts
new file mode 100644
index 0000000..bc156ea
--- /dev/null
+++ b/packages/services/billing-service/src/domain/entities/subscription.entity.ts
@@ -0,0 +1,42 @@
+import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn, UpdateDateColumn } from 'typeorm';
+
+export type SubscriptionStatus = 'trialing' | 'active' | 'past_due' | 'cancelled' | 'expired';
+
+@Entity({ name: 'subscriptions', schema: 'public' })
+export class Subscription {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ type: 'varchar', length: 100 })
+  tenantId!: string;
+
+  @Column({ type: 'uuid' })
+  planId!: string;
+
+  @Column({ type: 'varchar', length: 20, default: 'trialing' })
+  status!: SubscriptionStatus;
+
+  @Column({ type: 'timestamptz' })
+  currentPeriodStart!: Date;
+
+  @Column({ type: 'timestamptz' })
+  currentPeriodEnd!: Date;
+
+  @Column({ type: 'timestamptz', nullable: true })
+  trialEndsAt?: Date;
+
+  @Column({ type: 'timestamptz', nullable: true })
+  cancelledAt?: Date;
+
+  @Column({ type: 'boolean', default: false })
+  cancelAtPeriodEnd!: boolean;
+
+  @Column({ type: 'uuid', nullable: true })
+  nextPlanId?: string; // for scheduled downgrades
+
+  @CreateDateColumn({ type: 'timestamptz' })
+  createdAt!: Date;
+
+  @UpdateDateColumn({ type: 'timestamptz' })
+  updatedAt!: Date;
+}
diff --git a/packages/services/billing-service/src/domain/entities/usage-aggregate.entity.ts b/packages/services/billing-service/src/domain/entities/usage-aggregate.entity.ts
new file mode 100644
index 0000000..c7b3904
--- /dev/null
+++ b/packages/services/billing-service/src/domain/entities/usage-aggregate.entity.ts
@@ -0,0 +1,34 @@
+import { Entity, PrimaryGeneratedColumn, Column, UpdateDateColumn } from 'typeorm';
+
+@Entity({ name: 'usage_aggregates', schema: 'public' })
+export class UsageAggregate {
+  @PrimaryGeneratedColumn('uuid')
+  id!: string;
+
+  @Column({ type: 'varchar', length: 100 })
+  tenantId!: string;
+
+  @Column({ type: 'int' })
+  periodYear!: number;
+
+  @Column({ type: 'int' })
+  periodMonth!: number;
+
+  @Column({ type: 'bigint', default: 0 })
+  totalInputTokens!: number;
+
+  @Column({ type: 'bigint', default: 0 })
+  totalOutputTokens!: number;
+
+  @Column({ type: 'bigint', default: 0 })
+  totalTokens!: number;
+
+  @Column({ type: 'numeric', precision: 14, scale: 6, default: 0 })
+  totalCostUsd!: number;
+
+  @Column({ type: 'int', default: 0 })
+  taskCount!: number;
+
+  @UpdateDateColumn({ type: 'timestamptz' })
+  updatedAt!: Date;
+}
diff --git a/packages/services/billing-service/src/domain/ports/payment-provider.port.ts b/packages/services/billing-service/src/domain/ports/payment-provider.port.ts
new file mode 100644
index 0000000..0f38664
--- /dev/null
+++ b/packages/services/billing-service/src/domain/ports/payment-provider.port.ts
@@ -0,0 +1,44 @@
+export type PaymentProviderType = 'stripe' | 'alipay' | 'wechat_pay' | 'crypto';
+
+export interface CreatePaymentParams {
+  amount: number;           // in cents/fen
+  currency: string;         // 'USD' | 'CNY'
+  description: string;
+  tenantId: string;
+  invoiceId: string;
+  returnUrl: string;        // for redirect-based flows
+  cancelUrl?: string;
+  metadata?: Record<string, any>;
+}
+
+export interface PaymentSession {
+  providerPaymentId: string;
+  redirectUrl?: string;     // Alipay, WeChat, Crypto
+  qrCodeUrl?: string;       // WeChat Native Pay
+  clientSecret?: string;    // Stripe PaymentIntent
+  hostedUrl?: string;       // Coinbase Commerce
+  expiresAt?: Date;
+}
+
+export interface PaymentResult {
+  providerPaymentId: string;
+  status: 'succeeded' | 'failed' | 'pending';
+  amount: number;
+  currency: string;
+  paidAt?: Date;
+}
+
+export interface WebhookEvent {
+  eventType: 'payment_succeeded' | 'payment_failed' | 'refund_completed';
+  providerPaymentId: string;
+  amount: number;
+  currency: string;
+  metadata: Record<string, any>;
+}
+
+export interface PaymentProviderPort {
+  readonly providerType: PaymentProviderType;
+  createPaymentSession(params: CreatePaymentParams): Promise<PaymentSession>;
+  confirmPayment(providerPaymentId: string): Promise<PaymentResult>;
+  handleWebhook(payload: Buffer, headers: Record<string, string>): Promise<WebhookEvent>;
+}
diff --git a/packages/services/billing-service/src/domain/services/invoice-generator.service.ts b/packages/services/billing-service/src/domain/services/invoice-generator.service.ts
new file mode 100644
index 0000000..b012e9a
--- /dev/null
+++ b/packages/services/billing-service/src/domain/services/invoice-generator.service.ts
@@ -0,0 +1,134 @@
+import { Injectable } from '@nestjs/common';
+import { Invoice, InvoiceStatus, InvoiceCurrency } from '../entities/invoice.entity';
+import { InvoiceItem, InvoiceItemType } from '../entities/invoice-item.entity';
+import { Subscription } from '../entities/subscription.entity';
+import { Plan } from '../entities/plan.entity';
+import { UsageAggregate } from '../entities/usage-aggregate.entity';
+import { OverageCalculatorService } from './overage-calculator.service';
+
+@Injectable()
+export class InvoiceGeneratorService {
+  constructor(private readonly overageCalculator: OverageCalculatorService) {}
+
+  generateMonthlyInvoice(
+    subscription: Subscription,
+    plan: Plan,
+    usage: UsageAggregate,
+    currency: InvoiceCurrency = InvoiceCurrency.USD,
+    invoiceNumber: string,
+  ): { invoice: Invoice; items: InvoiceItem[] } {
+    const invoice = new Invoice();
+    invoice.tenantId = subscription.tenantId;
+    invoice.subscriptionId = subscription.id;
+    invoice.invoiceNumber = invoiceNumber;
+    invoice.status = InvoiceStatus.OPEN;
+    invoice.currency = currency;
+    invoice.periodStart = usage.periodStart;
+    invoice.periodEnd = usage.periodEnd;
+    invoice.dueDate = this.addDays(new Date(), 14);
+
+    const items: InvoiceItem[] = [];
+
+    // 1. Base subscription fee
+    const baseAmountCents =
+      currency === InvoiceCurrency.CNY ? plan.monthlyPriceCny : plan.monthlyPriceUsdCents;
+
+    if (baseAmountCents > 0) {
+      const subItem = new InvoiceItem();
+      subItem.itemType = InvoiceItemType.SUBSCRIPTION;
+      subItem.description = `${plan.displayName} subscription (${this.formatPeriod(usage.periodStart, usage.periodEnd)})`;
+      subItem.quantity = 1;
+      subItem.unitPrice = baseAmountCents;
+      subItem.amount = baseAmountCents;
+      subItem.currency = currency;
+      items.push(subItem);
+    }
+
+    // 2. Overage charges (token usage beyond plan quota)
+    if (plan.overageRateCentsPerMToken > 0 && usage.totalTokens > plan.includedTokensPerMonth) {
+      const overageResult = this.overageCalculator.calculate(
+        usage.totalTokens,
+        plan.includedTokensPerMonth,
+        plan.overageRateCentsPerMToken,
+      );
+
+      if (overageResult.overageAmountCents > 0) {
+        const overageItem = new InvoiceItem();
+        overageItem.itemType = InvoiceItemType.OVERAGE;
+        overageItem.description = `Token overage: ${this.formatTokens(overageResult.overageTokens)} tokens × ${this.formatRate(plan.overageRateCentsPerMToken, currency)}/MTok`;
+        overageItem.quantity = overageResult.overageTokens;
+        overageItem.unitPrice = plan.overageRateCentsPerMToken; // per million tokens
+        overageItem.amount = overageResult.overageAmountCents;
+        overageItem.currency = currency;
+        items.push(overageItem);
+      }
+    }
+
+    // Calculate totals
+    const subtotal = items.reduce((sum, item) => sum + item.amount, 0);
+    invoice.subtotalCents = subtotal;
+    invoice.taxCents = 0; // Tax calculation handled separately
+    invoice.totalCents = subtotal + invoice.taxCents;
+    invoice.amountDueCents = invoice.totalCents;
+
+    return { invoice, items };
+  }
+
+  /**
+   * Generate a proration invoice item for mid-cycle upgrades.
+   * Calculates the pro-rated difference between old and new plan for remaining days.
+   */
+  generateProratedUpgradeItem(
+    oldPlan: Plan,
+    newPlan: Plan,
+    upgradeDate: Date,
+    periodEnd: Date,
+    currency: InvoiceCurrency,
+  ): InvoiceItem {
+    const totalDays = this.daysBetween(
+      new Date(periodEnd.getFullYear(), periodEnd.getMonth() - 1, 1),
+      periodEnd,
+    );
+    const remainingDays = this.daysBetween(upgradeDate, periodEnd);
+    const fraction = remainingDays / totalDays;
+
+    const oldPrice = currency === InvoiceCurrency.CNY ? oldPlan.monthlyPriceCny : oldPlan.monthlyPriceUsdCents;
+    const newPrice = currency === InvoiceCurrency.CNY ? newPlan.monthlyPriceCny : newPlan.monthlyPriceUsdCents;
+    const proratedAmount = Math.round((newPrice - oldPrice) * fraction);
+
+    const item = new InvoiceItem();
+    item.itemType = InvoiceItemType.ADJUSTMENT;
+    item.description = `Plan upgrade proration: ${oldPlan.displayName} → ${newPlan.displayName} (${remainingDays}/${totalDays} days remaining)`;
+    item.quantity = 1;
+    item.unitPrice = proratedAmount;
+    item.amount = proratedAmount;
+    item.currency = currency;
+    return item;
+  }
+
+  private addDays(date: Date, days: number): Date {
+    const d = new Date(date);
+    d.setDate(d.getDate() + days);
+    return d;
+  }
+
+  private daysBetween(start: Date, end: Date): number {
+    const ms = end.getTime() - start.getTime();
+    return Math.ceil(ms / (1000 * 60 * 60 * 24));
+  }
+
+  private formatPeriod(start: Date, end: Date): string {
+    return `${start.toISOString().slice(0, 7)}`;
+  }
+
+  private formatTokens(tokens: number): string {
+    if (tokens >= 1_000_000) return `${(tokens / 1_000_000).toFixed(2)}M`;
+    if (tokens >= 1_000) return `${(tokens / 1_000).toFixed(0)}K`;
+    return `${tokens}`;
+  }
+
+  private formatRate(centsPerMToken: number, currency: InvoiceCurrency): string {
+    const symbol = currency === InvoiceCurrency.CNY ? '¥' : '$';
+    return `${symbol}${(centsPerMToken / 100).toFixed(2)}`;
+  }
+}
diff --git a/packages/services/billing-service/src/domain/services/overage-calculator.service.ts b/packages/services/billing-service/src/domain/services/overage-calculator.service.ts
new file mode 100644
index 0000000..595652e
--- /dev/null
+++ b/packages/services/billing-service/src/domain/services/overage-calculator.service.ts
@@ -0,0 +1,23 @@
+import { Injectable } from '@nestjs/common';
+
+export interface OverageResult {
+  overageTokens: number;
+  overageMTokens: number;
+  overageCentsUsd: number;
+}
+
+@Injectable()
+export class OverageCalculatorService {
+  /**
+   * Calculate overage charges for tokens consumed beyond the included quota.
+   * @param totalTokens - total tokens consumed in the period
+   * @param includedTokens - tokens included in the plan (no extra charge)
+   * @param overageRateCentsPerMToken - price per 1M overage tokens in USD cents
+   */
+  calculate(totalTokens: number, includedTokens: number, overageRateCentsPerMToken: number): OverageResult {
+    const overageTokens = Math.max(0, totalTokens - includedTokens);
+    const overageMTokens = overageTokens / 1_000_000;
+    const overageCentsUsd = Math.ceil(overageMTokens * overageRateCentsPerMToken);
+    return { overageTokens, overageMTokens, overageCentsUsd };
+  }
+}
diff --git a/packages/services/billing-service/src/domain/services/subscription-lifecycle.service.ts b/packages/services/billing-service/src/domain/services/subscription-lifecycle.service.ts
new file mode 100644
index 0000000..38ff4ef
--- /dev/null
+++ b/packages/services/billing-service/src/domain/services/subscription-lifecycle.service.ts
@@ -0,0 +1,92 @@
+import { Injectable } from '@nestjs/common';
+import { Subscription, SubscriptionStatus } from '../entities/subscription.entity';
+import { Plan } from '../entities/plan.entity';
+
+@Injectable()
+export class SubscriptionLifecycleService {
+  createTrial(tenantId: string, plan: Plan): Subscription {
+    const now = new Date();
+    const sub = new Subscription();
+    sub.tenantId = tenantId;
+    sub.planId = plan.id;
+    sub.status = 'trialing';
+    sub.currentPeriodStart = now;
+    sub.currentPeriodEnd = this.addDays(now, plan.trialDays);
+    sub.trialEndsAt = sub.currentPeriodEnd;
+    return sub;
+  }
+
+  activate(sub: Subscription): Subscription {
+    sub.status = 'active';
+    // Start full billing period from now
+    const now = new Date();
+    sub.currentPeriodStart = now;
+    sub.currentPeriodEnd = this.addMonths(now, 1);
+    sub.trialEndsAt = undefined;
+    return sub;
+  }
+
+  renew(sub: Subscription): Subscription {
+    sub.currentPeriodStart = sub.currentPeriodEnd;
+    sub.currentPeriodEnd = this.addMonths(sub.currentPeriodEnd, 1);
+    sub.status = 'active';
+    // Apply scheduled downgrade if any
+    if (sub.nextPlanId) {
+      sub.planId = sub.nextPlanId;
+      sub.nextPlanId = undefined;
+    }
+    return sub;
+  }
+
+  upgradeNow(sub: Subscription, newPlanId: string): Subscription {
+    sub.planId = newPlanId;
+    sub.nextPlanId = undefined;
+    if (sub.status === 'trialing') {
+      sub.status = 'active';
+    }
+    return sub;
+  }
+
+  scheduleDowngrade(sub: Subscription, newPlanId: string): Subscription {
+    sub.nextPlanId = newPlanId;
+    sub.cancelAtPeriodEnd = false;
+    return sub;
+  }
+
+  cancel(sub: Subscription, immediate: boolean): Subscription {
+    if (immediate) {
+      sub.status = 'cancelled';
+      sub.cancelledAt = new Date();
+    } else {
+      sub.cancelAtPeriodEnd = true;
+    }
+    return sub;
+  }
+
+  markPastDue(sub: Subscription): Subscription {
+    sub.status = 'past_due';
+    return sub;
+  }
+
+  expire(sub: Subscription): Subscription {
+    sub.status = 'expired';
+    sub.cancelledAt = new Date();
+    return sub;
+  }
+
+  isActive(sub: Subscription): boolean {
+    return sub.status === 'active' || sub.status === 'trialing';
+  }
+
+  private addDays(date: Date, days: number): Date {
+    const d = new Date(date);
+    d.setDate(d.getDate() + days);
+    return d;
+  }
+
+  private addMonths(date: Date, months: number): Date {
+    const d = new Date(date);
+    d.setMonth(d.getMonth() + months);
+    return d;
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/payment-providers/alipay/alipay.provider.ts b/packages/services/billing-service/src/infrastructure/payment-providers/alipay/alipay.provider.ts
new file mode 100644
index 0000000..4f60a6d
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/payment-providers/alipay/alipay.provider.ts
@@ -0,0 +1,101 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import {
+  PaymentProviderPort,
+  PaymentProviderType,
+  PaymentSessionRequest,
+  PaymentSession,
+  WebhookResult,
+} from '../../../domain/ports/payment-provider.port';
+import { InvoiceCurrency } from '../../../domain/entities/invoice.entity';
+
+@Injectable()
+export class AlipayProvider implements PaymentProviderPort {
+  readonly providerType = PaymentProviderType.ALIPAY;
+  private readonly logger = new Logger(AlipayProvider.name);
+  private appId: string;
+  private privateKey: string;
+  private configured = false;
+
+  constructor(private readonly configService: ConfigService) {
+    this.appId = this.configService.get<string>('ALIPAY_APP_ID', '');
+    this.privateKey = this.configService.get<string>('ALIPAY_PRIVATE_KEY', '');
+    this.configured = !!(this.appId && this.privateKey);
+  }
+
+  isConfigured(): boolean {
+    return this.configured;
+  }
+
+  async createPaymentSession(req: PaymentSessionRequest): Promise<PaymentSession> {
+    if (!this.configured) throw new Error('Alipay not configured');
+
+    // For CNY: use amount directly; for USD: this should not happen but handle gracefully
+    if (req.currency !== InvoiceCurrency.CNY) {
+      throw new Error('Alipay only supports CNY payments');
+    }
+
+    // Dynamic import to avoid load errors when alipay-sdk is not installed
+    const AlipaySdk = (await import('alipay-sdk')).default;
+    const client = new AlipaySdk({
+      appId: this.appId,
+      privateKey: this.privateKey,
+      signType: 'RSA2',
+      gateway: 'https://openapi.alipay.com/gateway.do',
+    });
+
+    // alipay amount is in yuan (CNY fen / 100)
+    const amountYuan = (req.amountCents / 100).toFixed(2);
+    const outTradeNo = `it0-${req.invoiceId}-${Date.now()}`;
+
+    // PC scan QR code payment
+    const result = await client.exec('alipay.trade.precreate', {
+      bizContent: {
+        out_trade_no: outTradeNo,
+        total_amount: amountYuan,
+        subject: req.description,
+      },
+    });
+
+    return {
+      sessionId: outTradeNo,
+      providerPaymentId: outTradeNo,
+      qrCodeUrl: result.qrCode,
+      redirectUrl: undefined,
+      clientSecret: undefined,
+      expiresAt: new Date(Date.now() + 2 * 60 * 60 * 1000), // 2 hours
+    };
+  }
+
+  async handleWebhook(rawBody: Buffer, headers: Record<string, string>): Promise<WebhookResult> {
+    if (!this.configured) throw new Error('Alipay not configured');
+
+    // Parse URL-encoded body
+    const params = new URLSearchParams(rawBody.toString());
+    const notifyData: Record<string, string> = {};
+    params.forEach((v, k) => { notifyData[k] = v; });
+
+    // Verify Alipay signature using alipay-sdk
+    const AlipaySdk = (await import('alipay-sdk')).default;
+    const client = new AlipaySdk({
+      appId: this.appId,
+      privateKey: this.privateKey,
+      signType: 'RSA2',
+      gateway: 'https://openapi.alipay.com/gateway.do',
+    });
+
+    const isValid = client.checkNotifySign(notifyData);
+    if (!isValid) throw new Error('Alipay webhook signature invalid');
+
+    const tradeStatus = notifyData['trade_status'];
+    const outTradeNo = notifyData['out_trade_no'];
+
+    if (tradeStatus === 'TRADE_SUCCESS' || tradeStatus === 'TRADE_FINISHED') {
+      return { type: 'payment_succeeded', providerPaymentId: outTradeNo };
+    } else if (tradeStatus === 'TRADE_CLOSED') {
+      return { type: 'payment_failed', providerPaymentId: outTradeNo };
+    }
+
+    return { type: 'unknown' };
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/payment-providers/crypto/crypto.provider.ts b/packages/services/billing-service/src/infrastructure/payment-providers/crypto/crypto.provider.ts
new file mode 100644
index 0000000..29915f1
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/payment-providers/crypto/crypto.provider.ts
@@ -0,0 +1,101 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import * as crypto from 'crypto';
+import {
+  PaymentProviderPort,
+  PaymentProviderType,
+  PaymentSessionRequest,
+  PaymentSession,
+  WebhookResult,
+} from '../../../domain/ports/payment-provider.port';
+
+@Injectable()
+export class CryptoProvider implements PaymentProviderPort {
+  readonly providerType = PaymentProviderType.CRYPTO;
+  private readonly logger = new Logger(CryptoProvider.name);
+  private apiKey: string;
+  private webhookSecret: string;
+  private configured = false;
+
+  private static readonly BASE_URL = 'https://api.commerce.coinbase.com';
+
+  constructor(private readonly configService: ConfigService) {
+    this.apiKey = this.configService.get<string>('COINBASE_COMMERCE_API_KEY', '');
+    this.webhookSecret = this.configService.get<string>('COINBASE_COMMERCE_WEBHOOK_SECRET', '');
+    this.configured = !!(this.apiKey && this.webhookSecret);
+  }
+
+  isConfigured(): boolean {
+    return this.configured;
+  }
+
+  async createPaymentSession(req: PaymentSessionRequest): Promise<PaymentSession> {
+    if (!this.configured) throw new Error('Coinbase Commerce not configured');
+
+    // Convert cents to dollar amount
+    const amount = (req.amountCents / 100).toFixed(2);
+
+    const response = await fetch(`${CryptoProvider.BASE_URL}/charges`, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'X-CC-Api-Key': this.apiKey,
+        'X-CC-Version': '2018-03-22',
+      },
+      body: JSON.stringify({
+        name: 'IT0 Platform',
+        description: req.description,
+        local_price: { amount, currency: 'USD' },
+        pricing_type: 'fixed_price',
+        metadata: {
+          invoiceId: req.invoiceId,
+          tenantId: req.tenantId,
+        },
+        redirect_url: req.returnUrl,
+      }),
+    });
+
+    if (!response.ok) {
+      const text = await response.text();
+      throw new Error(`Coinbase Commerce API error ${response.status}: ${text}`);
+    }
+
+    const data = await response.json();
+    const charge = data.data;
+
+    return {
+      sessionId: charge.id,
+      providerPaymentId: charge.id,
+      redirectUrl: charge.hosted_url,
+      qrCodeUrl: undefined,
+      clientSecret: undefined,
+      expiresAt: new Date(charge.expires_at),
+    };
+  }
+
+  async handleWebhook(rawBody: Buffer, headers: Record<string, string>): Promise<WebhookResult> {
+    if (!this.configured) throw new Error('Coinbase Commerce not configured');
+
+    const signature = headers['x-cc-webhook-signature'];
+    const expectedSig = crypto
+      .createHmac('sha256', this.webhookSecret)
+      .update(rawBody)
+      .digest('hex');
+
+    if (!crypto.timingSafeEqual(Buffer.from(signature, 'hex'), Buffer.from(expectedSig, 'hex'))) {
+      throw new Error('Coinbase Commerce webhook signature invalid');
+    }
+
+    const payload = JSON.parse(rawBody.toString());
+    const eventType = payload.event?.type;
+    const chargeCode = payload.event?.data?.code;
+
+    if (eventType === 'charge:confirmed' || eventType === 'charge:resolved') {
+      return { type: 'payment_succeeded', providerPaymentId: chargeCode };
+    } else if (eventType === 'charge:failed' || eventType === 'charge:delayed') {
+      return { type: 'payment_failed', providerPaymentId: chargeCode };
+    }
+
+    return { type: 'unknown' };
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/payment-providers/payment-provider.registry.ts b/packages/services/billing-service/src/infrastructure/payment-providers/payment-provider.registry.ts
new file mode 100644
index 0000000..12c00a5
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/payment-providers/payment-provider.registry.ts
@@ -0,0 +1,31 @@
+import { Injectable, Optional } from '@nestjs/common';
+import { PaymentProviderPort, PaymentProviderType } from '../../domain/ports/payment-provider.port';
+import { StripeProvider } from './stripe/stripe.provider';
+import { AlipayProvider } from './alipay/alipay.provider';
+import { WeChatPayProvider } from './wechat/wechat-pay.provider';
+import { CryptoProvider } from './crypto/crypto.provider';
+
+@Injectable()
+export class PaymentProviderRegistry {
+  private readonly providers = new Map<PaymentProviderType, PaymentProviderPort>();
+
+  constructor(
+    @Optional() stripe: StripeProvider,
+    @Optional() alipay: AlipayProvider,
+    @Optional() wechat: WeChatPayProvider,
+    @Optional() crypto: CryptoProvider,
+  ) {
+    if (stripe?.isConfigured()) this.providers.set(PaymentProviderType.STRIPE, stripe);
+    if (alipay?.isConfigured()) this.providers.set(PaymentProviderType.ALIPAY, alipay);
+    if (wechat?.isConfigured()) this.providers.set(PaymentProviderType.WECHAT_PAY, wechat);
+    if (crypto?.isConfigured()) this.providers.set(PaymentProviderType.CRYPTO, crypto);
+  }
+
+  get(type: PaymentProviderType): PaymentProviderPort | undefined {
+    return this.providers.get(type);
+  }
+
+  getAvailable(): PaymentProviderType[] {
+    return Array.from(this.providers.keys());
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/payment-providers/stripe/stripe.provider.ts b/packages/services/billing-service/src/infrastructure/payment-providers/stripe/stripe.provider.ts
new file mode 100644
index 0000000..05651ed
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/payment-providers/stripe/stripe.provider.ts
@@ -0,0 +1,82 @@
+import { Injectable } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import Stripe from 'stripe';
+import {
+  PaymentProviderPort,
+  PaymentProviderType,
+  PaymentSessionRequest,
+  PaymentSession,
+  WebhookResult,
+} from '../../../domain/ports/payment-provider.port';
+
+@Injectable()
+export class StripeProvider implements PaymentProviderPort {
+  readonly providerType = PaymentProviderType.STRIPE;
+  private client: Stripe | null = null;
+  private webhookSecret: string;
+
+  constructor(private readonly configService: ConfigService) {
+    const secretKey = this.configService.get<string>('STRIPE_SECRET_KEY');
+    this.webhookSecret = this.configService.get<string>('STRIPE_WEBHOOK_SECRET', '');
+    if (secretKey) {
+      this.client = new Stripe(secretKey, { apiVersion: '2024-11-20.acacia' });
+    }
+  }
+
+  isConfigured(): boolean {
+    return !!this.client;
+  }
+
+  async createPaymentSession(req: PaymentSessionRequest): Promise<PaymentSession> {
+    if (!this.client) throw new Error('Stripe not configured');
+
+    const intent = await this.client.paymentIntents.create({
+      amount: req.amountCents,
+      currency: req.currency.toLowerCase(),
+      metadata: {
+        invoiceId: req.invoiceId,
+        tenantId: req.tenantId,
+      },
+      description: req.description,
+    });
+
+    return {
+      sessionId: intent.id,
+      providerPaymentId: intent.id,
+      clientSecret: intent.client_secret ?? undefined,
+      redirectUrl: undefined,
+      qrCodeUrl: undefined,
+      expiresAt: new Date(Date.now() + 30 * 60 * 1000), // 30 minutes
+    };
+  }
+
+  async handleWebhook(rawBody: Buffer, headers: Record<string, string>): Promise<WebhookResult> {
+    if (!this.client) throw new Error('Stripe not configured');
+
+    const sig = headers['stripe-signature'];
+    let event: Stripe.Event;
+
+    try {
+      event = this.client.webhooks.constructEvent(rawBody, sig, this.webhookSecret);
+    } catch (err) {
+      throw new Error(`Stripe webhook signature verification failed: ${err.message}`);
+    }
+
+    switch (event.type) {
+      case 'payment_intent.succeeded': {
+        const intent = event.data.object as Stripe.PaymentIntent;
+        return { type: 'payment_succeeded', providerPaymentId: intent.id, metadata: intent.metadata };
+      }
+      case 'payment_intent.payment_failed': {
+        const intent = event.data.object as Stripe.PaymentIntent;
+        return { type: 'payment_failed', providerPaymentId: intent.id };
+      }
+      case 'charge.refunded': {
+        const charge = event.data.object as Stripe.Charge;
+        return { type: 'refunded', providerPaymentId: charge.payment_intent as string };
+      }
+      default:
+        return { type: 'unknown' };
+    }
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/payment-providers/wechat/wechat-pay.provider.ts b/packages/services/billing-service/src/infrastructure/payment-providers/wechat/wechat-pay.provider.ts
new file mode 100644
index 0000000..dbd3bec
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/payment-providers/wechat/wechat-pay.provider.ts
@@ -0,0 +1,156 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import * as crypto from 'crypto';
+import {
+  PaymentProviderPort,
+  PaymentProviderType,
+  PaymentSessionRequest,
+  PaymentSession,
+  WebhookResult,
+} from '../../../domain/ports/payment-provider.port';
+import { InvoiceCurrency } from '../../../domain/entities/invoice.entity';
+
+@Injectable()
+export class WeChatPayProvider implements PaymentProviderPort {
+  readonly providerType = PaymentProviderType.WECHAT_PAY;
+  private readonly logger = new Logger(WeChatPayProvider.name);
+  private mchId: string;
+  private apiKeyV3: string;
+  private appId: string;
+  private configured = false;
+
+  // WeChat Pay v3 API base
+  private static readonly BASE_URL = 'https://api.mch.weixin.qq.com';
+
+  constructor(private readonly configService: ConfigService) {
+    this.mchId = this.configService.get<string>('WECHAT_MCH_ID', '');
+    this.apiKeyV3 = this.configService.get<string>('WECHAT_API_KEY_V3', '');
+    this.appId = this.configService.get<string>('WECHAT_APP_ID', '');
+    this.configured = !!(this.mchId && this.apiKeyV3 && this.appId);
+  }
+
+  isConfigured(): boolean {
+    return this.configured;
+  }
+
+  async createPaymentSession(req: PaymentSessionRequest): Promise<PaymentSession> {
+    if (!this.configured) throw new Error('WeChat Pay not configured');
+
+    if (req.currency !== InvoiceCurrency.CNY) {
+      throw new Error('WeChat Pay only supports CNY payments');
+    }
+
+    const outTradeNo = `it0-${req.invoiceId}-${Date.now()}`;
+    const notifyUrl = this.configService.get<string>(
+      'WECHAT_NOTIFY_URL',
+      'https://it0api.szaiai.com/api/v1/billing/webhooks/wechat',
+    );
+
+    const body = {
+      appid: this.appId,
+      mchid: this.mchId,
+      description: req.description,
+      out_trade_no: outTradeNo,
+      notify_url: notifyUrl,
+      amount: { total: req.amountCents, currency: 'CNY' },
+    };
+
+    const response = await this.request('POST', '/v3/pay/transactions/native', body);
+    const qrCodeUrl = response.code_url;
+
+    return {
+      sessionId: outTradeNo,
+      providerPaymentId: outTradeNo,
+      qrCodeUrl,
+      redirectUrl: undefined,
+      clientSecret: undefined,
+      expiresAt: new Date(Date.now() + 2 * 60 * 60 * 1000),
+    };
+  }
+
+  async handleWebhook(rawBody: Buffer, headers: Record<string, string>): Promise<WebhookResult> {
+    if (!this.configured) throw new Error('WeChat Pay not configured');
+
+    // Verify HMAC-SHA256 signature
+    const timestamp = headers['wechatpay-timestamp'];
+    const nonce = headers['wechatpay-nonce'];
+    const signature = headers['wechatpay-signature'];
+    const message = `${timestamp}\n${nonce}\n${rawBody.toString()}\n`;
+
+    const expectedSig = crypto
+      .createHmac('sha256', this.apiKeyV3)
+      .update(message)
+      .digest('base64');
+
+    if (signature !== expectedSig) {
+      throw new Error('WeChat Pay webhook signature invalid');
+    }
+
+    const payload = JSON.parse(rawBody.toString());
+    const eventType = payload.event_type;
+
+    if (eventType === 'TRANSACTION.SUCCESS') {
+      // Decrypt resource
+      const resource = payload.resource;
+      const decrypted = this.decryptResource(resource.ciphertext, resource.associated_data, resource.nonce);
+      const transaction = JSON.parse(decrypted);
+      return { type: 'payment_succeeded', providerPaymentId: transaction.out_trade_no };
+    } else if (eventType === 'TRANSACTION.FAIL') {
+      const resource = payload.resource;
+      const decrypted = this.decryptResource(resource.ciphertext, resource.associated_data, resource.nonce);
+      const transaction = JSON.parse(decrypted);
+      return { type: 'payment_failed', providerPaymentId: transaction.out_trade_no };
+    }
+
+    return { type: 'unknown' };
+  }
+
+  private decryptResource(ciphertext: string, associatedData: string, nonce: string): string {
+    const key = Buffer.from(this.apiKeyV3, 'utf-8');
+    const ciphertextBuffer = Buffer.from(ciphertext, 'base64');
+    const authTag = ciphertextBuffer.slice(-16);
+    const encrypted = ciphertextBuffer.slice(0, -16);
+
+    const decipher = crypto.createDecipheriv('aes-256-gcm', key, nonce);
+    decipher.setAuthTag(authTag);
+    decipher.setAAD(Buffer.from(associatedData));
+
+    return Buffer.concat([decipher.update(encrypted), decipher.final()]).toString('utf-8');
+  }
+
+  private async request(method: string, path: string, body: any): Promise<any> {
+    const url = `${WeChatPayProvider.BASE_URL}${path}`;
+    const timestamp = Math.floor(Date.now() / 1000);
+    const nonce = crypto.randomBytes(16).toString('hex');
+    const bodyStr = JSON.stringify(body);
+    const message = `${method}\n${path}\n${timestamp}\n${nonce}\n${bodyStr}\n`;
+
+    // HMAC-SHA256 signature for request
+    const signature = crypto
+      .createHmac('sha256', this.apiKeyV3)
+      .update(message)
+      .digest('base64');
+
+    const authorization =
+      `WECHATPAY2-SHA256-RSA2048 mchid="${this.mchId}",` +
+      `nonce_str="${nonce}",timestamp="${timestamp}",` +
+      `signature="${signature}"`;
+
+    const res = await fetch(url, {
+      method,
+      headers: {
+        'Content-Type': 'application/json',
+        Authorization: authorization,
+        Accept: 'application/json',
+      },
+      body: bodyStr,
+    });
+
+    if (!res.ok) {
+      const text = await res.text();
+      throw new Error(`WeChat Pay API error ${res.status}: ${text}`);
+    }
+
+    return res.json();
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/repositories/invoice.repository.ts b/packages/services/billing-service/src/infrastructure/repositories/invoice.repository.ts
new file mode 100644
index 0000000..74746a5
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/repositories/invoice.repository.ts
@@ -0,0 +1,78 @@
+import { Injectable } from '@nestjs/common';
+import { DataSource, Repository } from 'typeorm';
+import { Invoice, InvoiceStatus } from '../../domain/entities/invoice.entity';
+import { InvoiceItem } from '../../domain/entities/invoice-item.entity';
+
+@Injectable()
+export class InvoiceRepository {
+  private readonly repo: Repository<Invoice>;
+  private readonly itemRepo: Repository<InvoiceItem>;
+
+  constructor(private readonly dataSource: DataSource) {
+    this.repo = this.dataSource.getRepository(Invoice);
+    this.itemRepo = this.dataSource.getRepository(InvoiceItem);
+  }
+
+  async findByTenantId(tenantId: string, limit = 20, offset = 0): Promise<[Invoice[], number]> {
+    return this.repo.findAndCount({
+      where: { tenantId },
+      order: { createdAt: 'DESC' },
+      take: limit,
+      skip: offset,
+    });
+  }
+
+  async findById(id: string): Promise<Invoice | null> {
+    return this.repo.findOne({ where: { id }, relations: ['items'] });
+  }
+
+  async findByInvoiceNumber(invoiceNumber: string): Promise<Invoice | null> {
+    return this.repo.findOne({ where: { invoiceNumber } });
+  }
+
+  async findUnpaidByTenantId(tenantId: string): Promise<Invoice[]> {
+    return this.repo.find({
+      where: [
+        { tenantId, status: InvoiceStatus.OPEN },
+        { tenantId, status: InvoiceStatus.PAST_DUE },
+      ],
+    });
+  }
+
+  async getNextInvoiceNumber(): Promise<string> {
+    const result = await this.dataSource.query(
+      `SELECT nextval('billing_invoice_number_seq') AS seq`,
+    );
+    const seq = result[0]?.seq ?? Date.now();
+    const year = new Date().getFullYear();
+    return `INV-${year}-${String(seq).padStart(6, '0')}`;
+  }
+
+  async save(invoice: Invoice): Promise<Invoice> {
+    return this.repo.save(invoice);
+  }
+
+  async saveItems(items: InvoiceItem[]): Promise<InvoiceItem[]> {
+    return this.itemRepo.save(items);
+  }
+
+  async saveWithItems(invoice: Invoice, items: InvoiceItem[]): Promise<Invoice> {
+    const runner = this.dataSource.createQueryRunner();
+    await runner.connect();
+    await runner.startTransaction();
+    try {
+      const savedInvoice = await runner.manager.save(Invoice, invoice);
+      for (const item of items) {
+        item.invoiceId = savedInvoice.id;
+      }
+      await runner.manager.save(InvoiceItem, items);
+      await runner.commitTransaction();
+      return savedInvoice;
+    } catch (err) {
+      await runner.rollbackTransaction();
+      throw err;
+    } finally {
+      await runner.release();
+    }
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/repositories/payment.repository.ts b/packages/services/billing-service/src/infrastructure/repositories/payment.repository.ts
new file mode 100644
index 0000000..4ef75f4
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/repositories/payment.repository.ts
@@ -0,0 +1,59 @@
+import { Injectable } from '@nestjs/common';
+import { DataSource, Repository } from 'typeorm';
+import { Payment, PaymentStatus } from '../../domain/entities/payment.entity';
+import { PaymentMethod } from '../../domain/entities/payment-method.entity';
+
+@Injectable()
+export class PaymentRepository {
+  private readonly paymentRepo: Repository<Payment>;
+  private readonly methodRepo: Repository<PaymentMethod>;
+
+  constructor(private readonly dataSource: DataSource) {
+    this.paymentRepo = this.dataSource.getRepository(Payment);
+    this.methodRepo = this.dataSource.getRepository(PaymentMethod);
+  }
+
+  async findPaymentById(id: string): Promise<Payment | null> {
+    return this.paymentRepo.findOne({ where: { id } });
+  }
+
+  async findByProviderPaymentId(providerPaymentId: string): Promise<Payment | null> {
+    return this.paymentRepo.findOne({ where: { providerPaymentId } });
+  }
+
+  async findPaymentsByTenantId(tenantId: string, limit = 20): Promise<Payment[]> {
+    return this.paymentRepo.find({
+      where: { tenantId },
+      order: { createdAt: 'DESC' },
+      take: limit,
+    });
+  }
+
+  async savePayment(payment: Payment): Promise<Payment> {
+    return this.paymentRepo.save(payment);
+  }
+
+  // Payment Methods
+  async findMethodsByTenantId(tenantId: string): Promise<PaymentMethod[]> {
+    return this.methodRepo.find({
+      where: { tenantId },
+      order: { isDefault: 'DESC', createdAt: 'ASC' },
+    });
+  }
+
+  async findMethodById(id: string): Promise<PaymentMethod | null> {
+    return this.methodRepo.findOne({ where: { id } });
+  }
+
+  async saveMethod(method: PaymentMethod): Promise<PaymentMethod> {
+    return this.methodRepo.save(method);
+  }
+
+  async deleteMethod(id: string): Promise<void> {
+    await this.methodRepo.delete(id);
+  }
+
+  async clearDefaultMethods(tenantId: string): Promise<void> {
+    await this.methodRepo.update({ tenantId, isDefault: true }, { isDefault: false });
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/repositories/plan.repository.ts b/packages/services/billing-service/src/infrastructure/repositories/plan.repository.ts
new file mode 100644
index 0000000..7646d42
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/repositories/plan.repository.ts
@@ -0,0 +1,37 @@
+import { Injectable } from '@nestjs/common';
+import { DataSource, Repository } from 'typeorm';
+import { Plan } from '../../domain/entities/plan.entity';
+
+@Injectable()
+export class PlanRepository {
+  private readonly repo: Repository<Plan>;
+
+  constructor(private readonly dataSource: DataSource) {
+    this.repo = this.dataSource.getRepository(Plan);
+  }
+
+  async findAll(): Promise<Plan[]> {
+    return this.repo.find({ where: { isActive: true }, order: { monthlyPriceUsdCents: 'ASC' } });
+  }
+
+  async findById(id: string): Promise<Plan | null> {
+    return this.repo.findOne({ where: { id } });
+  }
+
+  async findByName(name: string): Promise<Plan | null> {
+    return this.repo.findOne({ where: { name } });
+  }
+
+  async save(plan: Plan): Promise<Plan> {
+    return this.repo.save(plan);
+  }
+
+  async upsertSeedPlans(plans: Partial<Plan>[]): Promise<void> {
+    for (const p of plans) {
+      const existing = await this.repo.findOne({ where: { name: p.name } });
+      if (!existing) {
+        await this.repo.save(this.repo.create(p));
+      }
+    }
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/repositories/subscription.repository.ts b/packages/services/billing-service/src/infrastructure/repositories/subscription.repository.ts
new file mode 100644
index 0000000..f54612e
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/repositories/subscription.repository.ts
@@ -0,0 +1,41 @@
+import { Injectable } from '@nestjs/common';
+import { DataSource, Repository } from 'typeorm';
+import { Subscription, SubscriptionStatus } from '../../domain/entities/subscription.entity';
+
+@Injectable()
+export class SubscriptionRepository {
+  private readonly repo: Repository<Subscription>;
+
+  constructor(private readonly dataSource: DataSource) {
+    this.repo = this.dataSource.getRepository(Subscription);
+  }
+
+  async findByTenantId(tenantId: string): Promise<Subscription | null> {
+    return this.repo.findOne({
+      where: { tenantId },
+      order: { createdAt: 'DESC' },
+    });
+  }
+
+  async findById(id: string): Promise<Subscription | null> {
+    return this.repo.findOne({ where: { id } });
+  }
+
+  async findExpired(): Promise<Subscription[]> {
+    return this.repo
+      .createQueryBuilder('s')
+      .where('s.currentPeriodEnd < NOW()')
+      .andWhere('s.status IN (:...statuses)', {
+        statuses: [SubscriptionStatus.ACTIVE, SubscriptionStatus.TRIALING],
+      })
+      .getMany();
+  }
+
+  async findCancelAtPeriodEnd(): Promise<Subscription[]> {
+    return this.repo.find({ where: { cancelAtPeriodEnd: true, status: SubscriptionStatus.ACTIVE } });
+  }
+
+  async save(subscription: Subscription): Promise<Subscription> {
+    return this.repo.save(subscription);
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/repositories/usage-aggregate.repository.ts b/packages/services/billing-service/src/infrastructure/repositories/usage-aggregate.repository.ts
new file mode 100644
index 0000000..80152ec
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/repositories/usage-aggregate.repository.ts
@@ -0,0 +1,68 @@
+import { Injectable } from '@nestjs/common';
+import { DataSource, Repository } from 'typeorm';
+import { UsageAggregate } from '../../domain/entities/usage-aggregate.entity';
+
+@Injectable()
+export class UsageAggregateRepository {
+  private readonly repo: Repository<UsageAggregate>;
+
+  constructor(private readonly dataSource: DataSource) {
+    this.repo = this.dataSource.getRepository(UsageAggregate);
+  }
+
+  async findByTenantAndPeriod(tenantId: string, year: number, month: number): Promise<UsageAggregate | null> {
+    return this.repo.findOne({ where: { tenantId, year, month } });
+  }
+
+  async findCurrentMonth(tenantId: string): Promise<UsageAggregate | null> {
+    const now = new Date();
+    return this.findByTenantAndPeriod(tenantId, now.getFullYear(), now.getMonth() + 1);
+  }
+
+  async findHistoryByTenantId(tenantId: string, limit = 12): Promise<UsageAggregate[]> {
+    return this.repo.find({
+      where: { tenantId },
+      order: { year: 'DESC', month: 'DESC' },
+      take: limit,
+    });
+  }
+
+  async upsertTokens(
+    tenantId: string,
+    year: number,
+    month: number,
+    inputTokens: number,
+    outputTokens: number,
+    costUsd: number,
+  ): Promise<void> {
+    const periodStart = new Date(year, month - 1, 1);
+    const periodEnd = new Date(year, month, 0, 23, 59, 59); // last day of month
+
+    await this.dataSource.query(
+      `
+      INSERT INTO billing_usage_aggregates
+        (id, tenant_id, year, month, period_start, period_end,
+         total_input_tokens, total_output_tokens, total_tokens,
+         total_cost_usd, task_count, created_at, updated_at)
+      VALUES
+        (gen_random_uuid(), $1, $2, $3, $4, $5, $6, $7, $8, $9, 1, NOW(), NOW())
+      ON CONFLICT (tenant_id, year, month)
+      DO UPDATE SET
+        total_input_tokens = billing_usage_aggregates.total_input_tokens + EXCLUDED.total_input_tokens,
+        total_output_tokens = billing_usage_aggregates.total_output_tokens + EXCLUDED.total_output_tokens,
+        total_tokens = billing_usage_aggregates.total_tokens + EXCLUDED.total_tokens,
+        total_cost_usd = billing_usage_aggregates.total_cost_usd + EXCLUDED.total_cost_usd,
+        task_count = billing_usage_aggregates.task_count + 1,
+        updated_at = NOW()
+      `,
+      [
+        tenantId, year, month, periodStart, periodEnd,
+        inputTokens, outputTokens, inputTokens + outputTokens, costUsd,
+      ],
+    );
+  }
+
+  async save(aggregate: UsageAggregate): Promise<UsageAggregate> {
+    return this.repo.save(aggregate);
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/scheduler/billing.scheduler.ts b/packages/services/billing-service/src/infrastructure/scheduler/billing.scheduler.ts
new file mode 100644
index 0000000..611fb7b
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/scheduler/billing.scheduler.ts
@@ -0,0 +1,26 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { Cron, CronExpression } from '@nestjs/schedule';
+import { GenerateMonthlyInvoiceUseCase } from '../../application/use-cases/generate-monthly-invoice.use-case';
+import { PlanSeedService } from '../seed/plan-seed.service';
+
+@Injectable()
+export class BillingScheduler {
+  private readonly logger = new Logger(BillingScheduler.name);
+
+  constructor(
+    private readonly generateMonthlyInvoice: GenerateMonthlyInvoiceUseCase,
+    private readonly planSeed: PlanSeedService,
+  ) {}
+
+  // Run on the 1st of each month at 00:05 UTC
+  @Cron('5 0 1 * *')
+  async handleMonthlyBilling() {
+    this.logger.log('Running monthly billing job...');
+    try {
+      await this.generateMonthlyInvoice.execute();
+      this.logger.log('Monthly billing job completed');
+    } catch (err) {
+      this.logger.error(`Monthly billing job failed: ${err.message}`);
+    }
+  }
+}
diff --git a/packages/services/billing-service/src/infrastructure/seed/plan-seed.service.ts b/packages/services/billing-service/src/infrastructure/seed/plan-seed.service.ts
new file mode 100644
index 0000000..d31c0c5
--- /dev/null
+++ b/packages/services/billing-service/src/infrastructure/seed/plan-seed.service.ts
@@ -0,0 +1,63 @@
+import { Injectable, Logger, OnModuleInit } from '@nestjs/common';
+import { PlanRepository } from '../repositories/plan.repository';
+
+const SEED_PLANS = [
+  {
+    name: 'free',
+    displayName: 'Free',
+    monthlyPriceUsdCents: 0,
+    monthlyPriceCny: 0,
+    includedTokensPerMonth: 100_000,
+    overageRateCentsPerMToken: 0,
+    maxServers: 5,
+    maxUsers: 3,
+    maxStandingOrders: 10,
+    hardLimitPercent: 100,
+    trialDays: 0,
+    isActive: true,
+  },
+  {
+    name: 'pro',
+    displayName: 'Pro',
+    monthlyPriceUsdCents: 4999, // $49.99
+    monthlyPriceCny: 34900, // ¥349.00
+    includedTokensPerMonth: 1_000_000,
+    overageRateCentsPerMToken: 800, // $8.00 per MTok
+    maxServers: 50,
+    maxUsers: 20,
+    maxStandingOrders: 100,
+    hardLimitPercent: 150,
+    trialDays: 14,
+    isActive: true,
+  },
+  {
+    name: 'enterprise',
+    displayName: 'Enterprise',
+    monthlyPriceUsdCents: 19999, // $199.99
+    monthlyPriceCny: 139900, // ¥1399.00
+    includedTokensPerMonth: 10_000_000,
+    overageRateCentsPerMToken: 500, // $5.00 per MTok
+    maxServers: -1,
+    maxUsers: -1,
+    maxStandingOrders: -1,
+    hardLimitPercent: 0, // no hard limit
+    trialDays: 14,
+    isActive: true,
+  },
+];
+
+@Injectable()
+export class PlanSeedService implements OnModuleInit {
+  private readonly logger = new Logger(PlanSeedService.name);
+
+  constructor(private readonly planRepo: PlanRepository) {}
+
+  async onModuleInit() {
+    try {
+      await this.planRepo.upsertSeedPlans(SEED_PLANS);
+      this.logger.log('Plan seed completed');
+    } catch (err) {
+      this.logger.error(`Plan seed failed: ${err.message}`);
+    }
+  }
+}
diff --git a/packages/services/billing-service/src/interfaces/rest/controllers/invoice.controller.ts b/packages/services/billing-service/src/interfaces/rest/controllers/invoice.controller.ts
new file mode 100644
index 0000000..12be928
--- /dev/null
+++ b/packages/services/billing-service/src/interfaces/rest/controllers/invoice.controller.ts
@@ -0,0 +1,109 @@
+import {
+  Controller, Get, Post, Param, Query, Headers, NotFoundException,
+} from '@nestjs/common';
+import { InvoiceRepository } from '../../../infrastructure/repositories/invoice.repository';
+import { UsageAggregateRepository } from '../../../infrastructure/repositories/usage-aggregate.repository';
+import { CreatePaymentSessionUseCase } from '../../../application/use-cases/create-payment-session.use-case';
+import { PaymentProviderRegistry } from '../../../infrastructure/payment-providers/payment-provider.registry';
+import { PaymentProviderType } from '../../../domain/ports/payment-provider.port';
+
+@Controller('api/v1/billing')
+export class InvoiceController {
+  constructor(
+    private readonly invoiceRepo: InvoiceRepository,
+    private readonly usageAggRepo: UsageAggregateRepository,
+    private readonly createPaymentSession: CreatePaymentSessionUseCase,
+    private readonly providerRegistry: PaymentProviderRegistry,
+  ) {}
+
+  @Get('invoices')
+  async listInvoices(
+    @Headers('x-tenant-id') tenantId: string,
+    @Query('limit') limit = 20,
+    @Query('offset') offset = 0,
+  ) {
+    const [invoices, total] = await this.invoiceRepo.findByTenantId(tenantId, +limit, +offset);
+    return {
+      data: invoices.map((inv) => ({
+        id: inv.id,
+        invoiceNumber: inv.invoiceNumber,
+        status: inv.status,
+        currency: inv.currency,
+        totalAmount: inv.totalCents / 100,
+        amountDue: inv.amountDueCents / 100,
+        periodStart: inv.periodStart,
+        periodEnd: inv.periodEnd,
+        dueDate: inv.dueDate,
+        paidAt: inv.paidAt,
+        createdAt: inv.createdAt,
+      })),
+      total,
+    };
+  }
+
+  @Get('invoices/:id')
+  async getInvoice(
+    @Headers('x-tenant-id') tenantId: string,
+    @Param('id') id: string,
+  ) {
+    const invoice = await this.invoiceRepo.findById(id);
+    if (!invoice || invoice.tenantId !== tenantId) throw new NotFoundException('Invoice not found');
+
+    return {
+      id: invoice.id,
+      invoiceNumber: invoice.invoiceNumber,
+      status: invoice.status,
+      currency: invoice.currency,
+      subtotal: invoice.subtotalCents / 100,
+      tax: invoice.taxCents / 100,
+      total: invoice.totalCents / 100,
+      amountDue: invoice.amountDueCents / 100,
+      periodStart: invoice.periodStart,
+      periodEnd: invoice.periodEnd,
+      dueDate: invoice.dueDate,
+      paidAt: invoice.paidAt,
+      items: (invoice.items ?? []).map((item) => ({
+        id: item.id,
+        itemType: item.itemType,
+        description: item.description,
+        quantity: item.quantity,
+        unitPrice: item.unitPrice / 100,
+        amount: item.amount / 100,
+      })),
+    };
+  }
+
+  @Post('invoices/:id/pay')
+  async createPayment(
+    @Headers('x-tenant-id') tenantId: string,
+    @Param('id') invoiceId: string,
+    @Query('provider') provider: PaymentProviderType,
+    @Query('returnUrl') returnUrl?: string,
+  ) {
+    return this.createPaymentSession.execute({ tenantId, invoiceId, provider, returnUrl });
+  }
+
+  @Get('usage/history')
+  async getUsageHistory(
+    @Headers('x-tenant-id') tenantId: string,
+    @Query('limit') limit = 12,
+  ) {
+    const history = await this.usageAggRepo.findHistoryByTenantId(tenantId, +limit);
+    return history.map((u) => ({
+      year: u.year,
+      month: u.month,
+      totalInputTokens: u.totalInputTokens,
+      totalOutputTokens: u.totalOutputTokens,
+      totalTokens: u.totalTokens,
+      totalCostUsd: u.totalCostUsd,
+      taskCount: u.taskCount,
+      periodStart: u.periodStart,
+      periodEnd: u.periodEnd,
+    }));
+  }
+
+  @Get('providers')
+  getAvailableProviders() {
+    return { providers: this.providerRegistry.getAvailable() };
+  }
+}
diff --git a/packages/services/billing-service/src/interfaces/rest/controllers/payment-method.controller.ts b/packages/services/billing-service/src/interfaces/rest/controllers/payment-method.controller.ts
new file mode 100644
index 0000000..51738d0
--- /dev/null
+++ b/packages/services/billing-service/src/interfaces/rest/controllers/payment-method.controller.ts
@@ -0,0 +1,67 @@
+import {
+  Controller, Get, Post, Delete, Patch, Param, Body, Headers, HttpCode, HttpStatus, NotFoundException,
+} from '@nestjs/common';
+import { PaymentRepository } from '../../../infrastructure/repositories/payment.repository';
+import { PaymentMethod } from '../../../domain/entities/payment-method.entity';
+import { PaymentProviderType } from '../../../domain/ports/payment-provider.port';
+
+@Controller('api/v1/billing/payment-methods')
+export class PaymentMethodController {
+  constructor(private readonly paymentRepo: PaymentRepository) {}
+
+  @Get()
+  async listMethods(@Headers('x-tenant-id') tenantId: string) {
+    const methods = await this.paymentRepo.findMethodsByTenantId(tenantId);
+    return methods.map((m) => ({
+      id: m.id,
+      provider: m.provider,
+      displayName: m.displayName,
+      isDefault: m.isDefault,
+      expiresAt: m.expiresAt,
+      createdAt: m.createdAt,
+    }));
+  }
+
+  @Post()
+  async addMethod(
+    @Headers('x-tenant-id') tenantId: string,
+    @Body() body: { provider: PaymentProviderType; displayName: string; providerCustomerId?: string },
+  ) {
+    const method = new PaymentMethod();
+    method.tenantId = tenantId;
+    method.provider = body.provider;
+    method.displayName = body.displayName;
+    method.providerCustomerId = body.providerCustomerId ?? null;
+    method.isDefault = false;
+
+    const saved = await this.paymentRepo.saveMethod(method);
+    return { id: saved.id, provider: saved.provider, displayName: saved.displayName };
+  }
+
+  @Patch(':id/default')
+  @HttpCode(HttpStatus.OK)
+  async setDefault(
+    @Headers('x-tenant-id') tenantId: string,
+    @Param('id') id: string,
+  ) {
+    const method = await this.paymentRepo.findMethodById(id);
+    if (!method || method.tenantId !== tenantId) throw new NotFoundException('Payment method not found');
+
+    await this.paymentRepo.clearDefaultMethods(tenantId);
+    method.isDefault = true;
+    await this.paymentRepo.saveMethod(method);
+    return { success: true };
+  }
+
+  @Delete(':id')
+  @HttpCode(HttpStatus.NO_CONTENT)
+  async deleteMethod(
+    @Headers('x-tenant-id') tenantId: string,
+    @Param('id') id: string,
+  ) {
+    const method = await this.paymentRepo.findMethodById(id);
+    if (!method || method.tenantId !== tenantId) throw new NotFoundException('Payment method not found');
+
+    await this.paymentRepo.deleteMethod(id);
+  }
+}
diff --git a/packages/services/billing-service/src/interfaces/rest/controllers/plan.controller.ts b/packages/services/billing-service/src/interfaces/rest/controllers/plan.controller.ts
new file mode 100644
index 0000000..b1a506a
--- /dev/null
+++ b/packages/services/billing-service/src/interfaces/rest/controllers/plan.controller.ts
@@ -0,0 +1,26 @@
+import { Controller, Get } from '@nestjs/common';
+import { PlanRepository } from '../../../infrastructure/repositories/plan.repository';
+
+@Controller('api/v1/billing/plans')
+export class PlanController {
+  constructor(private readonly planRepo: PlanRepository) {}
+
+  @Get()
+  async findAll() {
+    const plans = await this.planRepo.findAll();
+    return plans.map((p) => ({
+      id: p.id,
+      name: p.name,
+      displayName: p.displayName,
+      monthlyPriceUsd: p.monthlyPriceUsdCents / 100,
+      monthlyPriceCny: p.monthlyPriceCny / 100,
+      includedTokensPerMonth: p.includedTokensPerMonth,
+      overageRateUsdPerMToken: p.overageRateCentsPerMToken / 100,
+      maxServers: p.maxServers,
+      maxUsers: p.maxUsers,
+      maxStandingOrders: p.maxStandingOrders,
+      hardLimitPercent: p.hardLimitPercent,
+      trialDays: p.trialDays,
+    }));
+  }
+}
diff --git a/packages/services/billing-service/src/interfaces/rest/controllers/subscription.controller.ts b/packages/services/billing-service/src/interfaces/rest/controllers/subscription.controller.ts
new file mode 100644
index 0000000..9c79ce9
--- /dev/null
+++ b/packages/services/billing-service/src/interfaces/rest/controllers/subscription.controller.ts
@@ -0,0 +1,70 @@
+import {
+  Controller, Get, Post, Body, Headers, HttpCode, HttpStatus, NotFoundException,
+} from '@nestjs/common';
+import { SubscriptionRepository } from '../../../infrastructure/repositories/subscription.repository';
+import { PlanRepository } from '../../../infrastructure/repositories/plan.repository';
+import { ChangePlanUseCase } from '../../../application/use-cases/change-plan.use-case';
+import { CancelSubscriptionUseCase } from '../../../application/use-cases/cancel-subscription.use-case';
+import { CheckTokenQuotaUseCase } from '../../../application/use-cases/check-token-quota.use-case';
+import { InvoiceCurrency } from '../../../domain/entities/invoice.entity';
+
+@Controller('api/v1/billing')
+export class SubscriptionController {
+  constructor(
+    private readonly subscriptionRepo: SubscriptionRepository,
+    private readonly planRepo: PlanRepository,
+    private readonly changePlan: ChangePlanUseCase,
+    private readonly cancelSubscription: CancelSubscriptionUseCase,
+    private readonly checkQuota: CheckTokenQuotaUseCase,
+  ) {}
+
+  @Get('subscription')
+  async getSubscription(@Headers('x-tenant-id') tenantId: string) {
+    const sub = await this.subscriptionRepo.findByTenantId(tenantId);
+    if (!sub) throw new NotFoundException('No active subscription');
+
+    const plan = await this.planRepo.findById(sub.planId);
+    const nextPlan = sub.nextPlanId ? await this.planRepo.findById(sub.nextPlanId) : null;
+
+    return {
+      id: sub.id,
+      status: sub.status,
+      plan: plan ? { name: plan.name, displayName: plan.displayName } : null,
+      nextPlan: nextPlan ? { name: nextPlan.name, displayName: nextPlan.displayName } : null,
+      currentPeriodStart: sub.currentPeriodStart,
+      currentPeriodEnd: sub.currentPeriodEnd,
+      trialEndsAt: sub.trialEndsAt,
+      cancelAtPeriodEnd: sub.cancelAtPeriodEnd,
+      cancelledAt: sub.cancelledAt,
+    };
+  }
+
+  @Post('subscription/upgrade')
+  @HttpCode(HttpStatus.OK)
+  async upgradePlan(
+    @Headers('x-tenant-id') tenantId: string,
+    @Body() body: { planName: string; currency?: 'USD' | 'CNY' },
+  ) {
+    await this.changePlan.execute({
+      tenantId,
+      newPlanName: body.planName,
+      currency: body.currency === 'CNY' ? InvoiceCurrency.CNY : InvoiceCurrency.USD,
+    });
+    return { success: true };
+  }
+
+  @Post('subscription/cancel')
+  @HttpCode(HttpStatus.OK)
+  async cancelPlan(
+    @Headers('x-tenant-id') tenantId: string,
+    @Body() body: { immediate?: boolean },
+  ) {
+    await this.cancelSubscription.execute(tenantId, body.immediate ?? false);
+    return { success: true };
+  }
+
+  @Get('usage/current')
+  async getCurrentUsage(@Headers('x-tenant-id') tenantId: string) {
+    return this.checkQuota.execute(tenantId);
+  }
+}
diff --git a/packages/services/billing-service/src/interfaces/rest/controllers/webhook.controller.ts b/packages/services/billing-service/src/interfaces/rest/controllers/webhook.controller.ts
new file mode 100644
index 0000000..1aed59f
--- /dev/null
+++ b/packages/services/billing-service/src/interfaces/rest/controllers/webhook.controller.ts
@@ -0,0 +1,58 @@
+import {
+  Controller, Post, Req, Headers, HttpCode, HttpStatus, Logger, BadRequestException,
+} from '@nestjs/common';
+import { Request } from 'express';
+import { HandlePaymentWebhookUseCase } from '../../../application/use-cases/handle-payment-webhook.use-case';
+import { PaymentProviderType } from '../../../domain/ports/payment-provider.port';
+
+@Controller('api/v1/billing/webhooks')
+export class WebhookController {
+  private readonly logger = new Logger(WebhookController.name);
+
+  constructor(private readonly handleWebhook: HandlePaymentWebhookUseCase) {}
+
+  @Post('stripe')
+  @HttpCode(HttpStatus.OK)
+  async stripeWebhook(@Req() req: Request, @Headers() headers: Record<string, string>) {
+    return this.processWebhook(PaymentProviderType.STRIPE, req, headers);
+  }
+
+  @Post('alipay')
+  @HttpCode(HttpStatus.OK)
+  async alipayWebhook(@Req() req: Request, @Headers() headers: Record<string, string>) {
+    await this.processWebhook(PaymentProviderType.ALIPAY, req, headers);
+    // Alipay expects plain text "success" response
+    return 'success';
+  }
+
+  @Post('wechat')
+  @HttpCode(HttpStatus.OK)
+  async wechatWebhook(@Req() req: Request, @Headers() headers: Record<string, string>) {
+    await this.processWebhook(PaymentProviderType.WECHAT_PAY, req, headers);
+    return { code: 'SUCCESS', message: '成功' };
+  }
+
+  @Post('crypto')
+  @HttpCode(HttpStatus.OK)
+  async cryptoWebhook(@Req() req: Request, @Headers() headers: Record<string, string>) {
+    return this.processWebhook(PaymentProviderType.CRYPTO, req, headers);
+  }
+
+  private async processWebhook(
+    provider: PaymentProviderType,
+    req: Request,
+    headers: Record<string, string>,
+  ) {
+    const rawBody = (req as any).rawBody as Buffer;
+    if (!rawBody) {
+      throw new BadRequestException('Raw body not available — ensure rawBody middleware is enabled');
+    }
+
+    try {
+      await this.handleWebhook.execute(provider, rawBody, headers);
+    } catch (err) {
+      this.logger.error(`Webhook error for ${provider}: ${err.message}`);
+      throw err;
+    }
+  }
+}
diff --git a/packages/services/billing-service/src/main.ts b/packages/services/billing-service/src/main.ts
new file mode 100644
index 0000000..7376a5d
--- /dev/null
+++ b/packages/services/billing-service/src/main.ts
@@ -0,0 +1,33 @@
+import { NestFactory } from '@nestjs/core';
+import { Logger } from '@nestjs/common';
+import { ConfigService } from '@nestjs/config';
+import { BillingModule } from './billing.module';
+
+const logger = new Logger('BillingService');
+
+process.on('unhandledRejection', (reason) => {
+  logger.error(`Unhandled Rejection: ${reason}`);
+});
+process.on('uncaughtException', (error) => {
+  logger.error(`Uncaught Exception: ${error.message}`, error.stack);
+});
+
+async function bootstrap() {
+  const app = await NestFactory.create(BillingModule, {
+    // Enable raw body for webhook signature verification
+    rawBody: true,
+  });
+
+  const config = app.get(ConfigService);
+  const port = config.get<number>('BILLING_SERVICE_PORT', 3010);
+
+  app.enableCors();
+
+  await app.listen(port);
+  logger.log(`billing-service running on port ${port}`);
+}
+
+bootstrap().catch((err) => {
+  logger.error(`Failed to start billing-service: ${err.message}`, err.stack);
+  process.exit(1);
+});
diff --git a/packages/services/billing-service/tsconfig.json b/packages/services/billing-service/tsconfig.json
new file mode 100644
index 0000000..95f5641
--- /dev/null
+++ b/packages/services/billing-service/tsconfig.json
@@ -0,0 +1,21 @@
+{
+  "compilerOptions": {
+    "module": "commonjs",
+    "declaration": true,
+    "removeComments": true,
+    "emitDecoratorMetadata": true,
+    "experimentalDecorators": true,
+    "allowSyntheticDefaultImports": true,
+    "target": "ES2021",
+    "sourceMap": true,
+    "outDir": "./dist",
+    "baseUrl": "./",
+    "incremental": true,
+    "skipLibCheck": true,
+    "strictNullChecks": false,
+    "noImplicitAny": false,
+    "strictBindCallApply": false,
+    "forceConsistentCasingInFileNames": false,
+    "noFallthroughCasesInSwitch": false
+  }
+}
diff --git a/packages/services/inventory-service/src/interfaces/rest/controllers/server.controller.ts b/packages/services/inventory-service/src/interfaces/rest/controllers/server.controller.ts
index 1717908..88431a2 100644
--- a/packages/services/inventory-service/src/interfaces/rest/controllers/server.controller.ts
+++ b/packages/services/inventory-service/src/interfaces/rest/controllers/server.controller.ts
@@ -1,6 +1,7 @@
-import { Controller, Get, Post, Put, Delete, Body, Param, Query, NotFoundException } from '@nestjs/common';
+import { Controller, Get, Post, Put, Delete, Body, Param, Query, NotFoundException, HttpException, HttpStatus } from '@nestjs/common';
 import { ServerRepository } from '../../../infrastructure/repositories/server.repository';
 import { Server } from '../../../domain/entities/server.entity';
+import { TenantContextService } from '@it0/common';
 import * as crypto from 'crypto';
 
 @Controller('api/v1/inventory/servers')
@@ -25,6 +26,17 @@ export class ServerController {
 
   @Post()
   async createServer(@Body() body: any) {
+    // Quota enforcement
+    const tenant = TenantContextService.getTenant();
+    if (tenant && tenant.maxServers !== -1) {
+      const existing = await this.serverRepository.findAll();
+      if (existing.length >= tenant.maxServers) {
+        throw new HttpException(
+          { message: `Server quota exceeded (${existing.length}/${tenant.maxServers}). Upgrade your plan to add more servers.`, code: 'QUOTA_EXCEEDED' },
+          HttpStatus.TOO_MANY_REQUESTS,
+        );
+      }
+    }
     const server = new Server();
     server.id = crypto.randomUUID();
     server.tenantId = body.tenantId;
diff --git a/packages/services/ops-service/src/interfaces/rest/controllers/standing-order.controller.ts b/packages/services/ops-service/src/interfaces/rest/controllers/standing-order.controller.ts
index bf4f617..378bfb3 100644
--- a/packages/services/ops-service/src/interfaces/rest/controllers/standing-order.controller.ts
+++ b/packages/services/ops-service/src/interfaces/rest/controllers/standing-order.controller.ts
@@ -1,7 +1,8 @@
-import { Controller, Get, Post, Put, Patch, Param, Body, NotFoundException } from '@nestjs/common';
+import { Controller, Get, Post, Put, Patch, Param, Body, NotFoundException, HttpException, HttpStatus } from '@nestjs/common';
 import { StandingOrderRepository } from '../../../infrastructure/repositories/standing-order.repository';
 import { StandingOrderExecutionRepository } from '../../../infrastructure/repositories/standing-order-execution.repository';
 import { StandingOrder } from '../../../domain/entities/standing-order.entity';
+import { TenantContextService } from '@it0/common';
 import * as crypto from 'crypto';
 
 @Controller('api/v1/ops/standing-orders')
@@ -92,6 +93,19 @@ export class StandingOrderController {
 
   @Post()
   async createOrder(@Body() body: any) {
+    // Quota enforcement
+    const tenant = TenantContextService.getTenant();
+    if (tenant && tenant.maxStandingOrders !== -1) {
+      const existing = await this.standingOrderRepository.findAll();
+      const activeCount = existing.filter((o) => o.status === 'active').length;
+      if (activeCount >= tenant.maxStandingOrders) {
+        throw new HttpException(
+          { message: `Standing order quota exceeded (${activeCount}/${tenant.maxStandingOrders}). Upgrade your plan to create more.`, code: 'QUOTA_EXCEEDED' },
+          HttpStatus.TOO_MANY_REQUESTS,
+        );
+      }
+    }
+
     const order = new StandingOrder();
     order.id = crypto.randomUUID();
     order.tenantId = body.tenantId;
diff --git a/packages/shared/common/src/constants/event-patterns.ts b/packages/shared/common/src/constants/event-patterns.ts
index 5d027b7..6b97997 100644
--- a/packages/shared/common/src/constants/event-patterns.ts
+++ b/packages/shared/common/src/constants/event-patterns.ts
@@ -32,4 +32,10 @@ export const EventPatterns = {
 
   // audit events
   AUDIT_LOG_CREATED: 'audit.log.created',
+
+  // billing events
+  USAGE_RECORDED: 'usage.recorded',
+  SUBSCRIPTION_CHANGED: 'subscription.changed',
+  QUOTA_EXCEEDED: 'quota.exceeded',
+  PAYMENT_RECEIVED: 'payment.received',
 } as const;
diff --git a/packages/shared/common/src/interfaces/tenant-info.interface.ts b/packages/shared/common/src/interfaces/tenant-info.interface.ts
index 4578393..06a7987 100644
--- a/packages/shared/common/src/interfaces/tenant-info.interface.ts
+++ b/packages/shared/common/src/interfaces/tenant-info.interface.ts
@@ -3,4 +3,8 @@ export interface TenantInfo {
   tenantName: string;
   plan: 'free' | 'pro' | 'enterprise';
   schemaName: string;
+  maxServers: number;
+  maxUsers: number;
+  maxStandingOrders: number;
+  maxAgentTokensPerMonth: number;
 }
diff --git a/packages/shared/common/src/utils/tenant-context.service.ts b/packages/shared/common/src/utils/tenant-context.service.ts
index f051df1..5f73930 100644
--- a/packages/shared/common/src/utils/tenant-context.service.ts
+++ b/packages/shared/common/src/utils/tenant-context.service.ts
@@ -8,17 +8,21 @@ export class TenantContextService {
     return this.storage.run(tenant, fn);
   }
 
-  static getTenant(): TenantInfo {
+  static getTenant(): TenantInfo | null {
+    return this.storage.getStore() ?? null;
+  }
+
+  static getTenantOrThrow(): TenantInfo {
     const tenant = this.storage.getStore();
     if (!tenant) throw new Error('Tenant context not initialized');
     return tenant;
   }
 
   static getTenantId(): string {
-    return this.getTenant().tenantId;
+    return this.getTenantOrThrow().tenantId;
   }
 
   static getSchemaName(): string {
-    return this.getTenant().schemaName;
+    return this.getTenantOrThrow().schemaName;
   }
 }
diff --git a/packages/shared/database/src/migrations/002-create-tenant-schema-template.sql b/packages/shared/database/src/migrations/002-create-tenant-schema-template.sql
index e8bb73f..f58fc38 100644
--- a/packages/shared/database/src/migrations/002-create-tenant-schema-template.sql
+++ b/packages/shared/database/src/migrations/002-create-tenant-schema-template.sql
@@ -433,3 +433,21 @@ CREATE TABLE metric_snapshots (
 
 CREATE INDEX idx_metrics_server_type ON metric_snapshots(server_id, metric_type, recorded_at DESC);
 CREATE INDEX idx_metrics_recorded ON metric_snapshots(recorded_at);
+
+-- Usage Records (for billing metering)
+CREATE TABLE usage_records (
+    id              UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id       VARCHAR(20) NOT NULL,
+    task_id         UUID NOT NULL,
+    session_id      UUID NOT NULL,
+    engine_type     VARCHAR(30) NOT NULL,
+    input_tokens    INTEGER NOT NULL DEFAULT 0,
+    output_tokens   INTEGER NOT NULL DEFAULT 0,
+    total_tokens    INTEGER NOT NULL DEFAULT 0,
+    cost_usd        NUMERIC(10, 6) NOT NULL DEFAULT 0,
+    model           VARCHAR(100) NOT NULL DEFAULT '',
+    recorded_at     TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_usage_records_tenant_month ON usage_records(tenant_id, recorded_at DESC);
+CREATE INDEX idx_usage_records_task ON usage_records(task_id);
diff --git a/packages/shared/database/src/migrations/005-create-billing-tables.sql b/packages/shared/database/src/migrations/005-create-billing-tables.sql
new file mode 100644
index 0000000..4af58c1
--- /dev/null
+++ b/packages/shared/database/src/migrations/005-create-billing-tables.sql
@@ -0,0 +1,141 @@
+-- IT0 Billing Tables (public schema)
+-- Phase 2: Subscription management + invoicing
+
+-- Invoice number sequence
+CREATE SEQUENCE IF NOT EXISTS billing_invoice_number_seq START 1000;
+
+-- Plans
+CREATE TABLE IF NOT EXISTS billing_plans (
+    id                          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    name                        VARCHAR(50) NOT NULL UNIQUE,   -- free, pro, enterprise
+    display_name                VARCHAR(100) NOT NULL,
+    monthly_price_usd_cents     INTEGER NOT NULL DEFAULT 0,
+    monthly_price_cny           INTEGER NOT NULL DEFAULT 0,    -- in fen (1/100 yuan)
+    included_tokens_per_month   BIGINT NOT NULL DEFAULT 100000,
+    overage_rate_cents_per_m_token INTEGER NOT NULL DEFAULT 0, -- per million tokens
+    max_servers                 INTEGER NOT NULL DEFAULT 5,    -- -1 = unlimited
+    max_users                   INTEGER NOT NULL DEFAULT 3,
+    max_standing_orders         INTEGER NOT NULL DEFAULT 10,
+    hard_limit_percent          INTEGER NOT NULL DEFAULT 100,  -- 0 = no hard limit
+    trial_days                  INTEGER NOT NULL DEFAULT 0,
+    is_active                   BOOLEAN NOT NULL DEFAULT TRUE,
+    created_at                  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at                  TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Subscriptions
+CREATE TABLE IF NOT EXISTS billing_subscriptions (
+    id                    UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id             VARCHAR(20) NOT NULL REFERENCES it0_shared.tenants(id),
+    plan_id               UUID NOT NULL REFERENCES billing_plans(id),
+    status                VARCHAR(20) NOT NULL DEFAULT 'trialing',
+    current_period_start  TIMESTAMPTZ NOT NULL,
+    current_period_end    TIMESTAMPTZ NOT NULL,
+    trial_ends_at         TIMESTAMPTZ,
+    cancel_at_period_end  BOOLEAN NOT NULL DEFAULT FALSE,
+    cancelled_at          TIMESTAMPTZ,
+    next_plan_id          UUID REFERENCES billing_plans(id),
+    created_at            TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at            TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_billing_subs_tenant ON billing_subscriptions(tenant_id);
+CREATE INDEX IF NOT EXISTS idx_billing_subs_status ON billing_subscriptions(status);
+CREATE INDEX IF NOT EXISTS idx_billing_subs_period_end ON billing_subscriptions(current_period_end);
+
+-- Invoices
+CREATE TABLE IF NOT EXISTS billing_invoices (
+    id               UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id        VARCHAR(20) NOT NULL REFERENCES it0_shared.tenants(id),
+    subscription_id  UUID REFERENCES billing_subscriptions(id),
+    invoice_number   VARCHAR(50) NOT NULL UNIQUE,
+    status           VARCHAR(20) NOT NULL DEFAULT 'open',  -- open, paid, void, past_due, uncollectible
+    currency         VARCHAR(3) NOT NULL DEFAULT 'USD',
+    subtotal_cents   INTEGER NOT NULL DEFAULT 0,
+    tax_cents        INTEGER NOT NULL DEFAULT 0,
+    total_cents      INTEGER NOT NULL DEFAULT 0,
+    amount_due_cents INTEGER NOT NULL DEFAULT 0,
+    period_start     TIMESTAMPTZ NOT NULL,
+    period_end       TIMESTAMPTZ NOT NULL,
+    due_date         TIMESTAMPTZ NOT NULL,
+    paid_at          TIMESTAMPTZ,
+    created_at       TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at       TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_billing_invoices_tenant ON billing_invoices(tenant_id);
+CREATE INDEX IF NOT EXISTS idx_billing_invoices_status ON billing_invoices(status);
+
+-- Invoice Items
+CREATE TABLE IF NOT EXISTS billing_invoice_items (
+    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    invoice_id  UUID NOT NULL REFERENCES billing_invoices(id) ON DELETE CASCADE,
+    item_type   VARCHAR(30) NOT NULL,  -- subscription, overage, credit, adjustment
+    description TEXT NOT NULL,
+    quantity    BIGINT NOT NULL DEFAULT 1,
+    unit_price  INTEGER NOT NULL,      -- cents
+    amount      INTEGER NOT NULL,      -- cents
+    currency    VARCHAR(3) NOT NULL DEFAULT 'USD',
+    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_billing_items_invoice ON billing_invoice_items(invoice_id);
+
+-- Payments
+CREATE TABLE IF NOT EXISTS billing_payments (
+    id                   UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id            VARCHAR(20) NOT NULL REFERENCES it0_shared.tenants(id),
+    invoice_id           UUID NOT NULL REFERENCES billing_invoices(id),
+    provider             VARCHAR(20) NOT NULL,  -- stripe, alipay, wechat_pay, crypto
+    provider_payment_id  VARCHAR(255) NOT NULL UNIQUE,
+    amount_cents         INTEGER NOT NULL,
+    currency             VARCHAR(3) NOT NULL,
+    status               VARCHAR(20) NOT NULL DEFAULT 'pending',  -- pending, succeeded, failed, refunded
+    paid_at              TIMESTAMPTZ,
+    metadata             JSONB,
+    created_at           TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at           TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_billing_payments_tenant ON billing_payments(tenant_id);
+CREATE INDEX IF NOT EXISTS idx_billing_payments_provider_id ON billing_payments(provider_payment_id);
+
+-- Payment Methods
+CREATE TABLE IF NOT EXISTS billing_payment_methods (
+    id                   UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id            VARCHAR(20) NOT NULL REFERENCES it0_shared.tenants(id),
+    provider             VARCHAR(20) NOT NULL,
+    display_name         VARCHAR(200) NOT NULL,
+    provider_customer_id VARCHAR(255),
+    details              JSONB,  -- masked card info, alipay account, etc. NO raw card numbers
+    is_default           BOOLEAN NOT NULL DEFAULT FALSE,
+    expires_at           TIMESTAMPTZ,
+    created_at           TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at           TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX IF NOT EXISTS idx_billing_methods_tenant ON billing_payment_methods(tenant_id);
+
+-- Monthly Usage Aggregates
+CREATE TABLE IF NOT EXISTS billing_usage_aggregates (
+    id                   UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id            VARCHAR(20) NOT NULL REFERENCES it0_shared.tenants(id),
+    year                 INTEGER NOT NULL,
+    month                INTEGER NOT NULL,  -- 1-12
+    period_start         TIMESTAMPTZ NOT NULL,
+    period_end           TIMESTAMPTZ NOT NULL,
+    total_input_tokens   BIGINT NOT NULL DEFAULT 0,
+    total_output_tokens  BIGINT NOT NULL DEFAULT 0,
+    total_tokens         BIGINT NOT NULL DEFAULT 0,
+    total_cost_usd       NUMERIC(12, 6) NOT NULL DEFAULT 0,
+    task_count           INTEGER NOT NULL DEFAULT 0,
+    created_at           TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at           TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    UNIQUE(tenant_id, year, month)
+);
+
+CREATE INDEX IF NOT EXISTS idx_billing_usage_tenant_period ON billing_usage_aggregates(tenant_id, year, month);
+
+-- Add max_standing_orders column to tenants if missing
+ALTER TABLE it0_shared.tenants ADD COLUMN IF NOT EXISTS max_standing_orders INTEGER NOT NULL DEFAULT 10;
+ALTER TABLE it0_shared.tenants ADD COLUMN IF NOT EXISTS max_agent_tokens_per_month BIGINT NOT NULL DEFAULT 100000;
diff --git a/packages/shared/database/src/run-migrations.ts b/packages/shared/database/src/run-migrations.ts
index c0c1a16..b511cf9 100644
--- a/packages/shared/database/src/run-migrations.ts
+++ b/packages/shared/database/src/run-migrations.ts
@@ -66,6 +66,10 @@ async function runSharedSchema(client: Client) {
   log('Running 001-create-shared-schema.sql ...');
   await runSqlFile(client, path.join(MIGRATIONS_DIR, '001-create-shared-schema.sql'));
   log('Shared schema created.');
+
+  log('Running 005-create-billing-tables.sql ...');
+  await runSqlFile(client, path.join(MIGRATIONS_DIR, '005-create-billing-tables.sql'));
+  log('Billing tables created.');
 }
 
 async function runTenantSchema(client: Client, tenantId: string) {
diff --git a/packages/shared/database/src/tenant-context.middleware.ts b/packages/shared/database/src/tenant-context.middleware.ts
index 798b1f2..a5695dd 100644
--- a/packages/shared/database/src/tenant-context.middleware.ts
+++ b/packages/shared/database/src/tenant-context.middleware.ts
@@ -1,8 +1,37 @@
-import { Injectable, NestMiddleware } from '@nestjs/common';
+import { Injectable, NestMiddleware, Optional } from '@nestjs/common';
+import { DataSource } from 'typeorm';
 import { TenantContextService, TenantInfo } from '@it0/common';
 
+interface TenantRow {
+  id: string;
+  name: string;
+  plan: 'free' | 'pro' | 'enterprise';
+  max_servers: number;
+  max_users: number;
+  max_standing_orders: number;
+  max_agent_tokens_per_month: number;
+}
+
+interface CacheEntry {
+  info: TenantInfo;
+  expiresAt: number;
+}
+
+/** Default quota limits per plan (used when tenant row is missing) */
+const DEFAULT_QUOTAS: Record<string, Pick<TenantInfo, 'maxServers' | 'maxUsers' | 'maxStandingOrders' | 'maxAgentTokensPerMonth'>> = {
+  free:       { maxServers: 5,  maxUsers: 3,  maxStandingOrders: 10,  maxAgentTokensPerMonth: 100_000 },
+  pro:        { maxServers: 50, maxUsers: 20, maxStandingOrders: 100, maxAgentTokensPerMonth: 1_000_000 },
+  enterprise: { maxServers: -1, maxUsers: -1, maxStandingOrders: -1,  maxAgentTokensPerMonth: 10_000_000 },
+};
+
+const CACHE_TTL_MS = 5 * 60 * 1000; // 5 minutes
+
 @Injectable()
 export class TenantContextMiddleware implements NestMiddleware {
+  private readonly cache = new Map<string, CacheEntry>();
+
+  constructor(@Optional() private readonly dataSource: DataSource) {}
+
   use(req: any, res: any, next: () => void) {
     let tenantId = req.headers?.['x-tenant-id'] as string;
 
@@ -34,13 +63,73 @@ export class TenantContextMiddleware implements NestMiddleware {
       return next();
     }
 
-    const tenantInfo: TenantInfo = {
+    // Serve from cache when available (synchronous fast path)
+    const cached = this.cache.get(tenantId);
+    if (cached && cached.expiresAt > Date.now()) {
+      TenantContextService.run(cached.info, () => next());
+      return;
+    }
+
+    // Load from DB, then run the request in tenant context
+    this.loadTenantInfo(tenantId)
+      .then((tenantInfo) => {
+        TenantContextService.run(tenantInfo, () => next());
+      })
+      .catch(() => {
+        const fallback = this.buildFallback(tenantId, 'free');
+        TenantContextService.run(fallback, () => next());
+      });
+  }
+
+  private async loadTenantInfo(tenantId: string): Promise<TenantInfo> {
+    const schemaName = `it0_t_${tenantId}`;
+
+    if (!this.dataSource) {
+      return this.buildFallback(tenantId, 'free');
+    }
+
+    try {
+      const rows: TenantRow[] = await this.dataSource.query(
+        `SELECT id, name, plan, max_servers, max_users, max_standing_orders, max_agent_tokens_per_month
+         FROM public.tenants WHERE id = $1 LIMIT 1`,
+        [tenantId],
+      );
+
+      const row = rows[0];
+      const plan = (row?.plan ?? 'free') as 'free' | 'pro' | 'enterprise';
+      const defaults = DEFAULT_QUOTAS[plan] ?? DEFAULT_QUOTAS['free'];
+
+      const tenantInfo: TenantInfo = {
+        tenantId,
+        tenantName: row?.name ?? tenantId,
+        plan,
+        schemaName,
+        maxServers: row?.max_servers ?? defaults.maxServers,
+        maxUsers: row?.max_users ?? defaults.maxUsers,
+        maxStandingOrders: row?.max_standing_orders ?? defaults.maxStandingOrders,
+        maxAgentTokensPerMonth: row?.max_agent_tokens_per_month ?? defaults.maxAgentTokensPerMonth,
+      };
+
+      this.cache.set(tenantId, { info: tenantInfo, expiresAt: Date.now() + CACHE_TTL_MS });
+      return tenantInfo;
+    } catch {
+      return this.buildFallback(tenantId, 'free');
+    }
+  }
+
+  private buildFallback(tenantId: string, plan: 'free' | 'pro' | 'enterprise'): TenantInfo {
+    const defaults = DEFAULT_QUOTAS[plan] ?? DEFAULT_QUOTAS['free'];
+    return {
       tenantId,
       tenantName: tenantId,
-      plan: 'free',
+      plan,
       schemaName: `it0_t_${tenantId}`,
+      ...defaults,
     };
+  }
 
-    TenantContextService.run(tenantInfo, () => next());
+  /** Invalidate cached tenant info — call after plan upgrade/downgrade. */
+  invalidate(tenantId: string): void {
+    this.cache.delete(tenantId);
   }
 }
diff --git a/packages/shared/events/src/event-types.ts b/packages/shared/events/src/event-types.ts
index 891c87e..d1d0d01 100644
--- a/packages/shared/events/src/event-types.ts
+++ b/packages/shared/events/src/event-types.ts
@@ -56,9 +56,57 @@ export interface StandingOrderExecutedEvent extends BaseEvent {
   };
 }
 
+export interface UsageRecordedEvent extends BaseEvent {
+  type: 'usage.recorded';
+  payload: {
+    taskId: string;
+    sessionId: string;
+    engineType: string;
+    inputTokens: number;
+    outputTokens: number;
+    totalTokens: number;
+    costUsd: number;
+    model: string;
+  };
+}
+
+export interface SubscriptionChangedEvent extends BaseEvent {
+  type: 'subscription.changed';
+  payload: {
+    subscriptionId: string;
+    fromPlan: string;
+    toPlan: string;
+    status: string;
+  };
+}
+
+export interface QuotaExceededEvent extends BaseEvent {
+  type: 'quota.exceeded';
+  payload: {
+    quotaType: 'tokens' | 'servers' | 'users' | 'standing_orders';
+    current: number;
+    limit: number;
+  };
+}
+
+export interface PaymentReceivedEvent extends BaseEvent {
+  type: 'payment.received';
+  payload: {
+    invoiceId: string;
+    paymentId: string;
+    amount: number;
+    currency: string;
+    provider: string;
+  };
+}
+
 export type IT0Event =
   | CommandExecutedEvent
   | ApprovalRequiredEvent
   | AlertFiredEvent
   | TaskCompletedEvent
-  | StandingOrderExecutedEvent;
+  | StandingOrderExecutedEvent
+  | UsageRecordedEvent
+  | SubscriptionChangedEvent
+  | QuotaExceededEvent
+  | PaymentReceivedEvent;