feat(platform-service): add user plan update to auth module for Stripe webhooks

- Added auth repository updatePlan(userId, productId, plan) helper
- Stripe webhook handlers now sync plan changes into auth users container
- Handles checkout completion and cancellation downgrade paths
- Keeps existing backend sync behavior intact
- Verified: tsc --noEmit clean, 19 test files / 178 tests passing

services/platform-service/src/modules/auth/repository.ts

@@ -37,6 +37,28 @@ export async function create(user: UserDoc): Promise<UserDoc> {
   return resource as UserDoc;
 }
 
+export async function updatePlan(
+  id: string,
+  productId: string,
+  plan: UserDoc['plan']
+): Promise<UserDoc | null> {
+  try {
+    const { resource } = await container().item(id, id).read<UserDoc>();
+    if (!resource || resource.productId !== productId) return null;
+    const { resource: updated } = await container()
+      .item(id, id)
+      .replace<UserDoc>({
+        ...resource,
+        plan,
+        updatedAt: new Date().toISOString(),
+      });
+    if (!updated) return null;
+    return updated;
+  } catch {
+    return null;
+  }
+}
+
 export async function updateLastLogin(id: string): Promise<void> {
   try {
     const { resource } = await container().item(id, id).read<UserDoc>();

services/platform-service/src/modules/stripe/routes.ts

@@ -16,6 +16,7 @@ import { DEFAULT_PRODUCT_ID } from '../../lib/product-config.js';
 import { getRequestProductId } from '../../lib/request-context.js';
 import { getStripeForProduct, getPriceIds } from '../../lib/stripe.js';
 import { BadRequestError } from '../../lib/errors.js';
+import * as authRepo from '../auth/repository.js';
 import * as subRepo from '../subscriptions/repository.js';
 import type { SubscriptionDoc } from '../subscriptions/types.js';
 
@@ -134,6 +135,7 @@ export async function stripeRoutes(app: FastifyInstance) {
               currentPeriodStart: now.toISOString(),
               currentPeriodEnd: periodEnd.toISOString(),
             });
+            await authRepo.updatePlan(userId, eventProductId, plan as SubscriptionDoc['plan']);
           } else {
             await subRepo.createSubscription({
               id: `sub_${userId}_${Date.now()}`,
@@ -152,6 +154,7 @@ export async function stripeRoutes(app: FastifyInstance) {
               createdAt: now.toISOString(),
               updatedAt: now.toISOString(),
             });
+            await authRepo.updatePlan(userId, eventProductId, plan as SubscriptionDoc['plan']);
           }
 
           // Sync plan to backend users container
@@ -190,6 +193,7 @@ export async function stripeRoutes(app: FastifyInstance) {
             cancelAtPeriodEnd: sub.cancel_at_period_end,
             currentPeriodEnd: new Date(sub.current_period_end * 1000).toISOString(),
           });
+          await authRepo.updatePlan(existing.userId, eventProductId, existing.plan);
           // Sync plan to backend users container
           await syncUserPlan(existing.userId, existing.plan, app.log);
         }
@@ -206,6 +210,7 @@ export async function stripeRoutes(app: FastifyInstance) {
             plan: 'free',
             cancelAtPeriodEnd: false,
           });
+          await authRepo.updatePlan(existing.userId, eventProductId, 'free');
           // Sync plan downgrade to backend users container
           await syncUserPlan(existing.userId, 'free', app.log);
         }