Add account self-delete and subscription lifecycle sync (#34)

Soft-delete DELETE /api/user/ for authenticated users (hide conversations,
blacklist tokens, block staff self-delete). Sync Stripe portal cancel/change
via subscription.updated/deleted webhooks and expose cancel_at_period_end for
Account UI (chat_web_app#75 companion).

llm_be/finance/tests/test_webhooks.py

@@ -8,10 +8,13 @@ from rest_framework import status
 from rest_framework.test import APITestCase
 
 from chat_backend.tests.factories import make_company, make_user
-from finance.models import Invoice, Payment
+from finance.models import Invoice, Payment, UserSubscription
+from finance.services.plans import assign_plan_from_stripe, seed_subscription_plans
 from finance.services.webhooks import (
     dispatch_stripe_event,
     handle_checkout_session_completed,
+    handle_customer_subscription_deleted,
+    handle_customer_subscription_updated,
     handle_invoice_paid,
     handle_invoice_payment_failed,
 )
@@ -107,6 +110,66 @@ class WebhookHandlerUnitTestCase(APITestCase):
         )
         self.assertIsNone(result)
 
+    def test_checkout_assigns_plan_from_metadata(self):
+        seed_subscription_plans(update_existing=False)
+        session = {
+            "id": "cs_test_plan_meta",
+            "metadata": {"user_id": str(self.user.pk), "plan_slug": "founders"},
+            "customer": "cus_meta",
+            "subscription": "sub_meta",
+            "payment_intent": "pi_meta",
+            "payment_status": "paid",
+            "amount_total": 1000,
+            "currency": "usd",
+        }
+        handle_checkout_session_completed(session)
+        sub = self.user.subscription
+        self.assertEqual(sub.plan.slug, "founders")
+        self.assertEqual(sub.source, UserSubscription.Source.STRIPE)
+        self.assertEqual(sub.status, UserSubscription.Status.ACTIVE)
+
+    def test_subscription_updated_sets_cancel_at_period_end(self):
+        seed_subscription_plans(update_existing=False)
+        assign_plan_from_stripe(
+            self.user,
+            plan_slug="founders",
+            stripe_subscription_id="sub_cancel",
+        )
+        result = handle_customer_subscription_updated(
+            {
+                "id": "sub_cancel",
+                "status": "active",
+                "cancel_at_period_end": True,
+                "current_period_end": 1_700_259_200,
+                "metadata": {"user_id": str(self.user.pk), "plan_slug": "founders"},
+            }
+        )
+        self.assertIsNotNone(result)
+        sub = UserSubscription.objects.get(user=self.user)
+        self.assertTrue(sub.cancel_at_period_end)
+        self.assertEqual(sub.status, UserSubscription.Status.ACTIVE)
+        self.assertIsNotNone(sub.current_period_end)
+
+    def test_subscription_deleted_marks_canceled(self):
+        seed_subscription_plans(update_existing=False)
+        assign_plan_from_stripe(
+            self.user,
+            plan_slug="founders",
+            stripe_subscription_id="sub_gone",
+        )
+        result = handle_customer_subscription_deleted(
+            {
+                "id": "sub_gone",
+                "status": "canceled",
+                "current_period_end": 1_700_259_200,
+                "metadata": {"user_id": str(self.user.pk)},
+            }
+        )
+        self.assertIsNotNone(result)
+        sub = UserSubscription.objects.get(user=self.user)
+        self.assertEqual(sub.status, UserSubscription.Status.CANCELED)
+        self.assertFalse(sub.cancel_at_period_end)
+
 
 class StripeWebhookViewTestCase(APITestCase):
     def setUp(self):