Add multi-plan subscriptions, quotas, and token usage APIs

Implements #16/#17/#36: Founders/Standard/Pro/Business/Backer catalog,
Backer email whitelist, prompt-window + token-period gates, and
tokens_in/out on conversation/prompt + subscription usage APIs.

llm_be/chat_backend/consumers.py

@@ -27,7 +27,17 @@ from .services.title_generator import title_generator
 from .services.moderation_classifier import moderation_classifier, ModerationLabel
 from .services.prompt_classifier.prompt_classifier import PromptClassifier, PromptType
 from .services.data_analysis_service import AsyncDataAnalysisService
-from .utils import has_usable_user_prompt, is_heartbeat_payload, normalize_user_message
+from .utils import (
+    extract_token_usage,
+    has_usable_user_prompt,
+    is_heartbeat_payload,
+    normalize_user_message,
+)
+from finance.services.quotas import (
+    FeatureNotAllowed,
+    QuotaExceeded,
+    check_generation_allowed,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -47,6 +57,35 @@ def create_conversation(prompt, email, title):
     return conversation.id
 
 
+@database_sync_to_async
+def resolve_chat_user(email=None, conversation_id=None):
+    if email:
+        user = CustomUser.objects.filter(email__iexact=email).first()
+        if user:
+            return user
+    if conversation_id:
+        conversation = (
+            Conversation.objects.select_related("user")
+            .filter(id=conversation_id)
+            .first()
+        )
+        if conversation and conversation.user_id:
+            return conversation.user
+    return None
+
+
+@database_sync_to_async
+def enforce_generation_gates(user, feature="text_generation"):
+    return check_generation_allowed(user, feature=feature)
+
+
+@database_sync_to_async
+def enforce_feature_gate(user, feature):
+    from finance.services.quotas import assert_feature_allowed
+
+    assert_feature_allowed(user, feature)
+
+
 @database_sync_to_async
 def get_workspace(conversation_id):
     conversation = Conversation.objects.get(id=conversation_id)
@@ -262,6 +301,36 @@ class ChatConsumerAgain(AsyncWebsocketConsumer):
                 )
                 return
 
+            chat_user = await resolve_chat_user(
+                email=email, conversation_id=conversation_id
+            )
+            if chat_user is None:
+                await self.send_json_message(
+                    json.dumps(
+                        {
+                            "type": "error",
+                            "code": "user_not_found",
+                            "content": "Unable to resolve user for this chat session.",
+                        }
+                    )
+                )
+                return
+
+            try:
+                await enforce_generation_gates(chat_user, feature="text_generation")
+            except (QuotaExceeded, FeatureNotAllowed) as exc:
+                await self.send_json_message(
+                    json.dumps(
+                        {
+                            "type": "error",
+                            "code": exc.code,
+                            "content": exc.message,
+                            "details": getattr(exc, "details", {}),
+                        }
+                    )
+                )
+                return
+
             if not conversation_id:
                 # we need to create a new conversation
                 # we will generate a name for it too
@@ -334,11 +403,20 @@ class ChatConsumerAgain(AsyncWebsocketConsumer):
                     decoded_file = input_dict.get("decoded_file")
                     file_type = input_dict.get("file_type")
                     
-                    # Feature Flag: Image Generation
+                    # Feature Flag + plan gate: Image Generation
                     if prompt_type == PromptType.IMAGE_GENERATION:
                         if not getattr(settings, "ALLOW_IMAGE_GENERATION", False):
                              return {"type": "text", "content": "Image Generation is disabled."}
-                        # If enabled, proceed (assuming implementation exists, but user said "have it set to false for now")
+                        try:
+                            await enforce_feature_gate(
+                                chat_user, "image_generation"
+                            )
+                        except FeatureNotAllowed as exc:
+                            return {
+                                "type": "error",
+                                "code": exc.code,
+                                "content": exc.message,
+                            }
                         return {"type": "text", "content": "Image Generation is not supported at this time, but it will be soon."}
 
                     if prompt_type == PromptType.SEARCH:
@@ -446,7 +524,17 @@ class ChatConsumerAgain(AsyncWebsocketConsumer):
                 await self.send("END_OF_THE_STREAM_ENDER_GAME_42")
                 
                 await save_generated_message(conversation_id, full_response)
-                await finish_prompt_metric(prompt_metric, len(full_response))
+                tokens_in, tokens_out = extract_token_usage(
+                    response_generator_or_dict
+                    if isinstance(response_generator_or_dict, dict)
+                    else None
+                )
+                await finish_prompt_metric(
+                    prompt_metric,
+                    len(full_response),
+                    tokens_in=tokens_in,
+                    tokens_out=tokens_out,
+                )
 
         if bytes_data:
             logger.info("we have byte data")

llm_be/chat_backend/consumers_graph.py

@@ -22,7 +22,13 @@ from .services.title_generator import title_generator
 from .services.moderation_classifier import moderation_classifier, ModerationLabel
 from .services.prompt_classifier.prompt_classifier import PromptClassifier, PromptType
 from .services.data_analysis_service import AsyncDataAnalysisService
-from .utils import has_usable_user_prompt, is_heartbeat_payload, normalize_user_message
+from .utils import (
+    extract_token_usage,
+    has_usable_user_prompt,
+    is_heartbeat_payload,
+    normalize_user_message,
+)
+from finance.services.quotas import FeatureNotAllowed, QuotaExceeded, check_generation_allowed
 
 logger = logging.getLogger(__name__)
 
@@ -40,6 +46,35 @@ def create_conversation(prompt, email, title):
     conversation.save()
     return conversation.id
 
+
+@database_sync_to_async
+def resolve_chat_user(email=None, conversation_id=None):
+    if email:
+        user = CustomUser.objects.filter(email__iexact=email).first()
+        if user:
+            return user
+    if conversation_id:
+        conversation = (
+            Conversation.objects.select_related("user")
+            .filter(id=conversation_id)
+            .first()
+        )
+        if conversation and conversation.user_id:
+            return conversation.user
+    return None
+
+
+@database_sync_to_async
+def enforce_generation_gates(user, feature="text_generation"):
+    return check_generation_allowed(user, feature=feature)
+
+
+@database_sync_to_async
+def enforce_feature_gate(user, feature):
+    from finance.services.quotas import assert_feature_allowed
+
+    assert_feature_allowed(user, feature)
+
 @database_sync_to_async
 def get_workspace(conversation_id):
     conversation = Conversation.objects.get(id=conversation_id)
@@ -172,6 +207,7 @@ class ChatState(TypedDict):
     response_generator: Any # AsyncGenerator or dict
     error: Union[str, None]
     model_name: str
+    chat_user: Any
 
 
 # --- LangGraph Nodes ---
@@ -210,10 +246,22 @@ async def generation_node(state: ChatState) -> ChatState:
     decoded_file = state.get("decoded_file")
     file_type = state.get("file_type")
     
-    # Feature Flag: Image Generation
+    # Feature Flag + plan gate: Image Generation
     if prompt_type == PromptType.IMAGE_GENERATION:
         if not getattr(settings, "ALLOW_IMAGE_GENERATION", False):
              return {"response_generator": {"type": "text", "content": "Image Generation is disabled."}}
+        chat_user = state.get("chat_user")
+        if chat_user is not None:
+            try:
+                await enforce_feature_gate(chat_user, "image_generation")
+            except FeatureNotAllowed as exc:
+                return {
+                    "response_generator": {
+                        "type": "error",
+                        "code": exc.code,
+                        "content": exc.message,
+                    }
+                }
         return {"response_generator": {"type": "text", "content": "Image Generation is not supported at this time, but it will be soon."}}
 
     # Feature Flag: Internet Access
@@ -312,6 +360,36 @@ class ChatConsumerGraph(AsyncWebsocketConsumer):
                 )
                 return
 
+            chat_user = await resolve_chat_user(
+                email=email, conversation_id=conversation_id
+            )
+            if chat_user is None:
+                await self.send_json_message(
+                    json.dumps(
+                        {
+                            "type": "error",
+                            "code": "user_not_found",
+                            "content": "Unable to resolve user for this chat session.",
+                        }
+                    )
+                )
+                return
+
+            try:
+                await enforce_generation_gates(chat_user, feature="text_generation")
+            except (QuotaExceeded, FeatureNotAllowed) as exc:
+                await self.send_json_message(
+                    json.dumps(
+                        {
+                            "type": "error",
+                            "code": exc.code,
+                            "content": exc.message,
+                            "details": getattr(exc, "details", {}),
+                        }
+                    )
+                )
+                return
+
             if not conversation_id:
                 title = await title_generator.generate_async(message)
                 conversation_id = await create_conversation(message, email, title)
@@ -357,7 +435,8 @@ class ChatConsumerGraph(AsyncWebsocketConsumer):
                     "prompt_type": None,
                     "response_generator": None,
                     "error": None,
-                    "model_name": model
+                    "model_name": model,
+                    "chat_user": chat_user,
                 }
                 print("Initial State: ", initial_state)
 
@@ -387,4 +466,14 @@ class ChatConsumerGraph(AsyncWebsocketConsumer):
                 await self.send("END_OF_THE_STREAM_ENDER_GAME_42")
                 
                 await save_generated_message(conversation_id, full_response)
-                await finish_prompt_metric(prompt_metric, len(full_response))
+                tokens_in, tokens_out = extract_token_usage(
+                    response_generator_or_dict
+                    if isinstance(response_generator_or_dict, dict)
+                    else None
+                )
+                await finish_prompt_metric(
+                    prompt_metric,
+                    len(full_response),
+                    tokens_in=tokens_in,
+                    tokens_out=tokens_out,
+                )

llm_be/chat_backend/oauth.py

@@ -307,6 +307,8 @@ def upsert_identity(user: CustomUser, profile: ProviderProfile) -> OAuthIdentity
 
 
 def _create_sso_user(profile: ProviderProfile) -> CustomUser:
+    from finance.services.plans import try_redeem_backer_email
+
     company = Company.objects.create(
         name=f"{profile.email}'s workspace",
         state="NA",
@@ -323,6 +325,7 @@ def _create_sso_user(profile: ProviderProfile) -> CustomUser:
     )
     user.set_unusable_password()
     user.save()
+    try_redeem_backer_email(user)
     return user
 
 

llm_be/chat_backend/serializers.py

@@ -1,11 +1,14 @@
 from rest_framework_simplejwt.serializers import TokenObtainPairSerializer
 from rest_framework import serializers
+from django.db.models import Count, Q, Sum
+
 from .models import (
     CustomUser,
     Announcement,
     Company,
     Conversation,
     Prompt,
+    PromptMetric,
     Feedback,
     FEEDBACK_CATEGORIES,
     DocumentWorkspace,
@@ -48,12 +51,33 @@ class CustomUserSerializer(serializers.ModelSerializer):
     password = serializers.CharField(min_length=8, write_only=True)
     company = CompanySerializer()
     has_usable_password = serializers.BooleanField()
+    subscription = serializers.SerializerMethodField()
 
     class Meta:
         model = CustomUser
         fields = "__all__"
         extra_kwargs = {"password": {"write_only": True}}
 
+    def get_subscription(self, obj):
+        from finance.services.plans import needs_checkout, plan_to_dict
+        from finance.models import UserSubscription
+
+        try:
+            sub = obj.subscription
+        except UserSubscription.DoesNotExist:
+            return {
+                "plan": None,
+                "status": UserSubscription.Status.NONE,
+                "source": UserSubscription.Source.NONE,
+                "needs_checkout": True,
+            }
+        return {
+            "plan": plan_to_dict(sub.plan) if sub.plan_id else None,
+            "status": sub.status,
+            "source": sub.source,
+            "needs_checkout": needs_checkout(obj),
+        }
+
 
 class SelfServeRegistrationSerializer(serializers.Serializer):
     """Minimal payload for public self-serve sign-up (gated by settings)."""
@@ -79,6 +103,8 @@ class SelfServeRegistrationSerializer(serializers.Serializer):
         return email
 
     def create(self, validated_data):
+        from finance.services.plans import try_redeem_backer_email
+
         email = validated_data["email"]
         password = validated_data["password"]
         first_name = (validated_data.get("first_name") or "").strip()
@@ -102,16 +128,73 @@ class SelfServeRegistrationSerializer(serializers.Serializer):
             company=company,
             is_company_manager=True,
         )
+        try_redeem_backer_email(user)
         return user
 
 
+def _conversation_token_totals(conversation_id: int):
+    """
+    Sum PromptMetric tokens for a conversation.
+
+    Returns nulls when the provider never reported usage (never fabricate 0).
+    """
+    agg = PromptMetric.objects.filter(conversation_id=conversation_id).aggregate(
+        tin=Sum("tokens_in"),
+        tout=Sum("tokens_out"),
+        with_in=Count("id", filter=Q(tokens_in__isnull=False)),
+        with_out=Count("id", filter=Q(tokens_out__isnull=False)),
+    )
+    return (
+        agg["tin"] if agg["with_in"] else None,
+        agg["tout"] if agg["with_out"] else None,
+    )
+
+
+def _prompt_token_pair(prompt_id: int):
+    metric = (
+        PromptMetric.objects.filter(prompt_id=prompt_id)
+        .order_by("-created")
+        .only("tokens_in", "tokens_out")
+        .first()
+    )
+    if metric is None:
+        return None, None
+    return metric.tokens_in, metric.tokens_out
+
+
 class ConversationSerializer(serializers.ModelSerializer):
+    tokens_in = serializers.SerializerMethodField()
+    tokens_out = serializers.SerializerMethodField()
+
     class Meta:
         model = Conversation
-        fields = ("title", "created", "last_modified", "id")
+        fields = (
+            "title",
+            "created",
+            "last_modified",
+            "id",
+            "tokens_in",
+            "tokens_out",
+        )
+
+    def _token_pair(self, obj):
+        cache = self.context.setdefault("_conversation_token_cache", {})
+        if obj.id not in cache:
+            cache[obj.id] = _conversation_token_totals(obj.id)
+        return cache[obj.id]
+
+    def get_tokens_in(self, obj):
+        tin, _ = self._token_pair(obj)
+        return tin
+
+    def get_tokens_out(self, obj):
+        _, tout = self._token_pair(obj)
+        return tout
 
 
 class PromptSerializer(serializers.ModelSerializer):
+    tokens_in = serializers.SerializerMethodField()
+    tokens_out = serializers.SerializerMethodField()
 
     class Meta:
         model = Prompt
@@ -120,8 +203,24 @@ class PromptSerializer(serializers.ModelSerializer):
             "user_created",
             "created",
             "id",
+            "tokens_in",
+            "tokens_out",
         )
 
+    def _token_pair(self, obj):
+        cache = self.context.setdefault("_prompt_token_cache", {})
+        if obj.id not in cache:
+            cache[obj.id] = _prompt_token_pair(obj.id)
+        return cache[obj.id]
+
+    def get_tokens_in(self, obj):
+        tin, _ = self._token_pair(obj)
+        return tin
+
+    def get_tokens_out(self, obj):
+        _, tout = self._token_pair(obj)
+        return tout
+
     def validate_message(self, value: str) -> str:
         if value is None or not str(value).strip():
             raise serializers.ValidationError("Message text cannot be empty.")

llm_be/chat_backend/tests/test_serializers.py

@@ -38,7 +38,10 @@ class ConversationSerializerTestCase(TestCase):
 
         data = ConversationSerializer(conversation).data
 
-        self.assertEqual(set(data.keys()), {"title", "created", "last_modified", "id"})
+        self.assertEqual(
+            set(data.keys()),
+            {"title", "created", "last_modified", "id", "tokens_in", "tokens_out"},
+        )
         self.assertEqual(data["title"], "Weather Inquiry")
 
 

llm_be/chat_backend/views.py

@@ -136,6 +136,8 @@ class CustomUserCreate(APIView):
 
         user = serializer.save()
         refresh = RefreshToken.for_user(user)
+        from finance.services.plans import needs_checkout
+
         return Response(
             {
                 "email": user.email,
@@ -143,6 +145,7 @@ class CustomUserCreate(APIView):
                 "last_name": user.last_name,
                 "access": str(refresh.access_token),
                 "refresh": str(refresh),
+                "needs_checkout": needs_checkout(user),
             },
             status=status.HTTP_201_CREATED,
         )

llm_be/chat_backend/views_oauth.py

@@ -139,7 +139,9 @@ class OAuthCallbackView(APIView):
             return _redirect_error("server_error", "Unexpected OAuth error.")
 
         refresh = RefreshToken.for_user(user)
-        needs_checkout = "1" if created else "0"
+        from finance.services.plans import needs_checkout as user_needs_checkout
+
+        needs_checkout = "1" if (created and user_needs_checkout(user)) else "0"
         return HttpResponseRedirect(
             _frontend_callback_url(
                 access=str(refresh.access_token),

llm_be/finance/admin.py

@@ -1,6 +1,52 @@
 from django.contrib import admin
 
-from finance.models import Invoice, Payment
+from finance.models import BackerEmail, Invoice, Payment, SubscriptionPlan, UserSubscription
+
+
+@admin.register(SubscriptionPlan)
+class SubscriptionPlanAdmin(admin.ModelAdmin):
+    list_display = (
+        "slug",
+        "name",
+        "price_cents",
+        "is_public",
+        "is_selectable",
+        "allows_image_generation",
+        "allows_all_future_features",
+        "prompt_quota_per_window",
+        "prompt_window_hours",
+        "monthly_token_quota",
+        "sort_order",
+    )
+    list_filter = ("is_public", "is_selectable", "allows_image_generation")
+    search_fields = ("slug", "name", "stripe_price_id")
+    readonly_fields = ("created", "last_modified")
+    prepopulated_fields = {"slug": ("name",)}
+
+
+@admin.register(BackerEmail)
+class BackerEmailAdmin(admin.ModelAdmin):
+    list_display = ("email", "note", "redeemed_at", "redeemed_user", "created")
+    search_fields = ("email", "note", "redeemed_user__email")
+    raw_id_fields = ("redeemed_user",)
+    readonly_fields = ("created", "last_modified", "redeemed_at", "redeemed_user")
+
+
+@admin.register(UserSubscription)
+class UserSubscriptionAdmin(admin.ModelAdmin):
+    list_display = (
+        "user",
+        "plan",
+        "status",
+        "source",
+        "stripe_subscription_id",
+        "monthly_token_quota_override",
+        "created",
+    )
+    list_filter = ("status", "source", "plan")
+    search_fields = ("user__email", "user__username", "stripe_subscription_id")
+    raw_id_fields = ("user", "plan")
+    readonly_fields = ("created", "last_modified")
 
 
 class PaymentInline(admin.TabularInline):

llm_be/finance/apps.py

@@ -5,3 +5,10 @@ class FinanceConfig(AppConfig):
     default_auto_field = "django.db.models.BigAutoField"
     name = "finance"
     verbose_name = "Finance"
+
+    def ready(self):
+        from django.db.models.signals import post_migrate
+
+        from finance.signals import seed_plans_on_migrate
+
+        post_migrate.connect(seed_plans_on_migrate, sender=self)

llm_be/finance/migrations/0002_subscription_plans_quotas.py

@@ -0,0 +1,86 @@
+# Generated by Django 6.0 on 2026-07-31 11:14
+
+import django.db.models.deletion
+import django.utils.timezone
+from django.conf import settings
+from django.db import migrations, models
+
+
+def seed_plans(apps, schema_editor):
+    from finance.services.plans import seed_subscription_plans
+
+    seed_subscription_plans(update_existing=True)
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('finance', '0001_initial'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='SubscriptionPlan',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('created', models.DateTimeField(default=django.utils.timezone.now)),
+                ('last_modified', models.DateTimeField(default=django.utils.timezone.now)),
+                ('slug', models.SlugField(max_length=64, unique=True)),
+                ('name', models.CharField(max_length=128)),
+                ('description', models.TextField(blank=True, default='')),
+                ('price_cents', models.PositiveIntegerField(default=0, help_text='List price in cents (0 for complimentary tiers).')),
+                ('currency', models.CharField(default='usd', max_length=8)),
+                ('interval', models.CharField(default='month', max_length=16)),
+                ('stripe_price_id', models.CharField(blank=True, default='', help_text='Optional Stripe Price id; empty uses price_data at Checkout.', max_length=255)),
+                ('is_public', models.BooleanField(default=False, help_text='Shown in public pricing / plan list APIs.')),
+                ('is_selectable', models.BooleanField(default=False, help_text='Selectable at Checkout. Backer is never selectable.')),
+                ('allows_text_generation', models.BooleanField(default=True)),
+                ('allows_image_generation', models.BooleanField(default=False)),
+                ('allows_all_future_features', models.BooleanField(default=False, help_text='Founders/Backer: unlock new capabilities as they ship.')),
+                ('prompt_quota_per_window', models.PositiveIntegerField(help_text='Max prompts allowed in each rolling window.')),
+                ('prompt_window_hours', models.PositiveIntegerField(default=6, help_text='Length of the rolling prompt quota window in hours.')),
+                ('monthly_token_quota', models.PositiveIntegerField(blank=True, help_text='Optional billing-period token cap (tokens_in + tokens_out). Null = no token-period limit (prompt window still applies).', null=True)),
+                ('sort_order', models.PositiveIntegerField(default=0)),
+            ],
+            options={
+                'ordering': ['sort_order', 'price_cents', 'name'],
+            },
+        ),
+        migrations.CreateModel(
+            name='BackerEmail',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('created', models.DateTimeField(default=django.utils.timezone.now)),
+                ('last_modified', models.DateTimeField(default=django.utils.timezone.now)),
+                ('email', models.EmailField(db_index=True, max_length=254, unique=True)),
+                ('note', models.CharField(blank=True, default='', max_length=512)),
+                ('redeemed_at', models.DateTimeField(blank=True, null=True)),
+                ('redeemed_user', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='backer_email_entries', to=settings.AUTH_USER_MODEL)),
+            ],
+            options={
+                'verbose_name': 'Backer email',
+                'verbose_name_plural': 'Backer emails',
+                'ordering': ['email'],
+            },
+        ),
+        migrations.CreateModel(
+            name='UserSubscription',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('created', models.DateTimeField(default=django.utils.timezone.now)),
+                ('last_modified', models.DateTimeField(default=django.utils.timezone.now)),
+                ('status', models.CharField(choices=[('none', 'None'), ('active', 'Active'), ('past_due', 'Past due'), ('canceled', 'Canceled')], db_index=True, default='none', max_length=32)),
+                ('source', models.CharField(choices=[('none', 'None'), ('stripe', 'Stripe'), ('backer', 'Backer'), ('admin', 'Admin')], default='none', max_length=32)),
+                ('stripe_subscription_id', models.CharField(blank=True, db_index=True, default='', max_length=255)),
+                ('monthly_token_quota_override', models.PositiveIntegerField(blank=True, help_text='Optional per-user override of plan monthly_token_quota.', null=True)),
+                ('plan', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.PROTECT, related_name='subscriptions', to='finance.subscriptionplan')),
+                ('user', models.OneToOneField(on_delete=django.db.models.deletion.CASCADE, related_name='subscription', to=settings.AUTH_USER_MODEL)),
+            ],
+            options={
+                'verbose_name': 'User subscription',
+                'verbose_name_plural': 'User subscriptions',
+            },
+        ),
+        migrations.RunPython(seed_plans, migrations.RunPython.noop),
+    ]

llm_be/finance/models.py

@@ -5,6 +5,176 @@ from django.utils import timezone
 from chat_backend.models import Company, TimeInfoBase
 
 
+class SubscriptionPlan(TimeInfoBase):
+    """Catalog row for a billable (or complimentary) subscription tier."""
+
+    class Slug(models.TextChoices):
+        FOUNDERS = "founders", "Founders"
+        STANDARD = "standard", "Standard"
+        PRO = "pro", "Pro / Creator"
+        BUSINESS = "business", "Business Team"
+        BACKER = "backer", "Backer"
+
+    slug = models.SlugField(max_length=64, unique=True, db_index=True)
+    name = models.CharField(max_length=128)
+    description = models.TextField(blank=True, default="")
+    price_cents = models.PositiveIntegerField(
+        default=0,
+        help_text="List price in cents (0 for complimentary tiers).",
+    )
+    currency = models.CharField(max_length=8, default="usd")
+    interval = models.CharField(max_length=16, default="month")
+    stripe_price_id = models.CharField(
+        max_length=255,
+        blank=True,
+        default="",
+        help_text="Optional Stripe Price id; empty uses price_data at Checkout.",
+    )
+    is_public = models.BooleanField(
+        default=False,
+        help_text="Shown in public pricing / plan list APIs.",
+    )
+    is_selectable = models.BooleanField(
+        default=False,
+        help_text="Selectable at Checkout. Backer is never selectable.",
+    )
+    allows_text_generation = models.BooleanField(default=True)
+    allows_image_generation = models.BooleanField(default=False)
+    allows_all_future_features = models.BooleanField(
+        default=False,
+        help_text="Founders/Backer: unlock new capabilities as they ship.",
+    )
+    prompt_quota_per_window = models.PositiveIntegerField(
+        help_text="Max prompts allowed in each rolling window.",
+    )
+    prompt_window_hours = models.PositiveIntegerField(
+        default=6,
+        help_text="Length of the rolling prompt quota window in hours.",
+    )
+    monthly_token_quota = models.PositiveIntegerField(
+        null=True,
+        blank=True,
+        help_text=(
+            "Optional billing-period token cap (tokens_in + tokens_out). "
+            "Null = no token-period limit (prompt window still applies)."
+        ),
+    )
+    sort_order = models.PositiveIntegerField(default=0)
+
+    class Meta:
+        ordering = ["sort_order", "price_cents", "name"]
+
+    def __str__(self) -> str:
+        return f"{self.name} ({self.slug})"
+
+    def allows_feature(self, feature: str) -> bool:
+        if self.allows_all_future_features:
+            return True
+        if feature in ("text", "text_generation"):
+            return self.allows_text_generation
+        if feature in ("image", "image_generation"):
+            return self.allows_image_generation
+        return False
+
+
+class BackerEmail(TimeInfoBase):
+    """Pre-registered emails that receive complimentary Backer (Founders-level) access."""
+
+    email = models.EmailField(unique=True, db_index=True)
+    note = models.CharField(max_length=512, blank=True, default="")
+    redeemed_at = models.DateTimeField(null=True, blank=True)
+    redeemed_user = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        related_name="backer_email_entries",
+    )
+
+    class Meta:
+        ordering = ["email"]
+        verbose_name = "Backer email"
+        verbose_name_plural = "Backer emails"
+
+    def __str__(self) -> str:
+        return self.email
+
+    def save(self, *args, **kwargs):
+        if self.email:
+            self.email = self.email.strip().lower()
+        super().save(*args, **kwargs)
+
+
+class UserSubscription(TimeInfoBase):
+    """Per-user plan assignment (Stripe, Backer whitelist, or admin)."""
+
+    class Status(models.TextChoices):
+        NONE = "none", "None"
+        ACTIVE = "active", "Active"
+        PAST_DUE = "past_due", "Past due"
+        CANCELED = "canceled", "Canceled"
+
+    class Source(models.TextChoices):
+        NONE = "none", "None"
+        STRIPE = "stripe", "Stripe"
+        BACKER = "backer", "Backer"
+        ADMIN = "admin", "Admin"
+
+    user = models.OneToOneField(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="subscription",
+    )
+    plan = models.ForeignKey(
+        SubscriptionPlan,
+        on_delete=models.PROTECT,
+        related_name="subscriptions",
+        null=True,
+        blank=True,
+    )
+    status = models.CharField(
+        max_length=32,
+        choices=Status.choices,
+        default=Status.NONE,
+        db_index=True,
+    )
+    source = models.CharField(
+        max_length=32,
+        choices=Source.choices,
+        default=Source.NONE,
+    )
+    stripe_subscription_id = models.CharField(
+        max_length=255,
+        blank=True,
+        default="",
+        db_index=True,
+    )
+    monthly_token_quota_override = models.PositiveIntegerField(
+        null=True,
+        blank=True,
+        help_text="Optional per-user override of plan monthly_token_quota.",
+    )
+
+    class Meta:
+        verbose_name = "User subscription"
+        verbose_name_plural = "User subscriptions"
+
+    def __str__(self) -> str:
+        plan = self.plan.slug if self.plan_id else "none"
+        return f"UserSubscription user={self.user_id} plan={plan} ({self.status})"
+
+    @property
+    def is_active(self) -> bool:
+        return self.status == self.Status.ACTIVE and self.plan_id is not None
+
+    def effective_monthly_token_quota(self):
+        if self.monthly_token_quota_override is not None:
+            return self.monthly_token_quota_override
+        if self.plan_id:
+            return self.plan.monthly_token_quota
+        return None
+
+
 class Invoice(TimeInfoBase):
     """Local ledger row for a billed period / Stripe invoice or checkout session."""
 

llm_be/finance/serializers.py

@@ -1,6 +1,6 @@
 from rest_framework import serializers
 
-from finance.models import Invoice, Payment
+from finance.models import Invoice, Payment, SubscriptionPlan
 
 
 class InvoiceSerializer(serializers.ModelSerializer):
@@ -49,7 +49,38 @@ class PaymentSerializer(serializers.ModelSerializer):
 class CheckoutSessionSerializer(serializers.Serializer):
     success_url = serializers.URLField(required=False, allow_blank=False)
     cancel_url = serializers.URLField(required=False, allow_blank=False)
+    plan_slug = serializers.SlugField(required=False, allow_blank=False)
 
 
 class PortalSessionSerializer(serializers.Serializer):
     return_url = serializers.URLField(required=False, allow_blank=False)
+
+
+class SubscriptionPlanSerializer(serializers.ModelSerializer):
+    features = serializers.SerializerMethodField()
+
+    class Meta:
+        model = SubscriptionPlan
+        fields = [
+            "slug",
+            "name",
+            "description",
+            "price_cents",
+            "currency",
+            "interval",
+            "is_public",
+            "is_selectable",
+            "features",
+            "prompt_quota_per_window",
+            "prompt_window_hours",
+            "monthly_token_quota",
+            "sort_order",
+        ]
+        read_only_fields = fields
+
+    def get_features(self, obj):
+        return {
+            "text_generation": obj.allows_feature("text_generation"),
+            "image_generation": obj.allows_feature("image_generation"),
+            "all_future_features": obj.allows_all_future_features,
+        }

llm_be/finance/services/plans.py

@@ -0,0 +1,258 @@
+"""Subscription plan catalog helpers, seeding, and user assignment."""
+
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+from django.db import transaction
+from django.utils import timezone
+
+from finance.models import BackerEmail, SubscriptionPlan, UserSubscription
+
+logger = logging.getLogger(__name__)
+
+# Seed catalog for #36. Standard/Pro/Business stay hidden until explicitly enabled.
+PLAN_SEED: list[dict[str, Any]] = [
+    {
+        "slug": SubscriptionPlan.Slug.FOUNDERS,
+        "name": "Founders",
+        "description": (
+            "Unlimited product access for early supporters: text plus all future "
+            "capabilities as they ship. $10/mo."
+        ),
+        "price_cents": 1000,
+        "is_public": True,
+        "is_selectable": True,
+        "allows_text_generation": True,
+        "allows_image_generation": True,
+        "allows_all_future_features": True,
+        "prompt_quota_per_window": 300,
+        "prompt_window_hours": 6,
+        "monthly_token_quota": None,
+        "sort_order": 10,
+    },
+    {
+        "slug": SubscriptionPlan.Slug.STANDARD,
+        "name": "Standard",
+        "description": (
+            "Secure conversational chat and coding assistance for developers "
+            "and privacy-conscious individuals."
+        ),
+        "price_cents": 1500,
+        "is_public": False,
+        "is_selectable": False,
+        "allows_text_generation": True,
+        "allows_image_generation": False,
+        "allows_all_future_features": False,
+        "prompt_quota_per_window": 100,
+        "prompt_window_hours": 6,
+        "monthly_token_quota": 1_000_000,
+        "sort_order": 20,
+    },
+    {
+        "slug": SubscriptionPlan.Slug.PRO,
+        "name": "Pro / Creator",
+        "description": (
+            "Higher message caps and multi-modal workflows for heavy users, "
+            "including image generation when available."
+        ),
+        "price_cents": 4000,
+        "is_public": False,
+        "is_selectable": False,
+        "allows_text_generation": True,
+        "allows_image_generation": True,
+        "allows_all_future_features": False,
+        "prompt_quota_per_window": 200,
+        "prompt_window_hours": 6,
+        "monthly_token_quota": 3_000_000,
+        "sort_order": 30,
+    },
+    {
+        "slug": SubscriptionPlan.Slug.BUSINESS,
+        "name": "Business Team",
+        "description": (
+            "Team seats, centralized auth, priority support, and absolute data "
+            "privacy for local companies handling sensitive data."
+        ),
+        "price_cents": 9900,
+        "is_public": False,
+        "is_selectable": False,
+        "allows_text_generation": True,
+        "allows_image_generation": True,
+        "allows_all_future_features": False,
+        "prompt_quota_per_window": 300,
+        "prompt_window_hours": 6,
+        "monthly_token_quota": 5_000_000,
+        "sort_order": 40,
+    },
+    {
+        "slug": SubscriptionPlan.Slug.BACKER,
+        "name": "Backer",
+        "description": (
+            "Complimentary Founders-level access for pre-approved emails. "
+            "Not shown at checkout."
+        ),
+        "price_cents": 0,
+        "is_public": False,
+        "is_selectable": False,
+        "allows_text_generation": True,
+        "allows_image_generation": True,
+        "allows_all_future_features": True,
+        "prompt_quota_per_window": 300,
+        "prompt_window_hours": 6,
+        "monthly_token_quota": None,
+        "sort_order": 5,
+    },
+]
+
+
+def seed_subscription_plans(*, update_existing: bool = True) -> list[SubscriptionPlan]:
+    """Idempotently create/update the canonical plan catalog."""
+    plans: list[SubscriptionPlan] = []
+    for row in PLAN_SEED:
+        slug = row["slug"]
+        defaults = {k: v for k, v in row.items() if k != "slug"}
+        plan, created = SubscriptionPlan.objects.get_or_create(
+            slug=slug,
+            defaults=defaults,
+        )
+        if not created and update_existing:
+            for key, value in defaults.items():
+                setattr(plan, key, value)
+            plan.save()
+        plans.append(plan)
+    return plans
+
+
+def get_plan(slug: str) -> SubscriptionPlan | None:
+    return SubscriptionPlan.objects.filter(slug=slug).first()
+
+
+def get_or_create_user_subscription(user) -> UserSubscription:
+    sub, _ = UserSubscription.objects.get_or_create(user=user)
+    return sub
+
+
+def assign_plan(
+    user,
+    *,
+    plan: SubscriptionPlan,
+    source: str,
+    status: str = UserSubscription.Status.ACTIVE,
+    stripe_subscription_id: str = "",
+) -> UserSubscription:
+    sub = get_or_create_user_subscription(user)
+    sub.plan = plan
+    sub.source = source
+    sub.status = status
+    if stripe_subscription_id:
+        sub.stripe_subscription_id = stripe_subscription_id
+    sub.save()
+    return sub
+
+
+def user_has_active_plan(user) -> bool:
+    try:
+        sub = user.subscription
+    except UserSubscription.DoesNotExist:
+        return False
+    return sub.is_active
+
+
+def needs_checkout(user) -> bool:
+    """True when the user must complete paid Checkout to use the product."""
+    try:
+        sub = user.subscription
+    except UserSubscription.DoesNotExist:
+        return True
+    if not sub.is_active:
+        return True
+    # Complimentary / already-paid tiers skip Checkout.
+    if sub.source in (
+        UserSubscription.Source.BACKER,
+        UserSubscription.Source.ADMIN,
+        UserSubscription.Source.STRIPE,
+    ):
+        return False
+    return True
+
+
+@transaction.atomic
+def try_redeem_backer_email(user) -> UserSubscription | None:
+    """
+    If the user's email is on the Backer whitelist and unused, assign Backer plan.
+
+    Returns the UserSubscription when redeemed, else None.
+    """
+    email = (getattr(user, "email", "") or "").strip().lower()
+    if not email:
+        return None
+
+    entry = (
+        BackerEmail.objects.select_for_update()
+        .filter(email__iexact=email, redeemed_at__isnull=True)
+        .first()
+    )
+    if entry is None:
+        return None
+
+    seed_subscription_plans(update_existing=False)
+    plan = get_plan(SubscriptionPlan.Slug.BACKER)
+    if plan is None:
+        logger.error("Backer plan missing from catalog; cannot redeem %s", email)
+        return None
+
+    sub = assign_plan(
+        user,
+        plan=plan,
+        source=UserSubscription.Source.BACKER,
+        status=UserSubscription.Status.ACTIVE,
+    )
+    entry.redeemed_at = timezone.now()
+    entry.redeemed_user = user
+    entry.save(update_fields=["redeemed_at", "redeemed_user", "last_modified"])
+    logger.info("Redeemed Backer email %s for user %s", email, user.pk)
+    return sub
+
+
+def assign_founders_from_stripe(
+    user,
+    *,
+    stripe_subscription_id: str = "",
+) -> UserSubscription:
+    seed_subscription_plans(update_existing=False)
+    plan = get_plan(SubscriptionPlan.Slug.FOUNDERS)
+    if plan is None:
+        raise RuntimeError("Founders plan missing from catalog")
+    return assign_plan(
+        user,
+        plan=plan,
+        source=UserSubscription.Source.STRIPE,
+        status=UserSubscription.Status.ACTIVE,
+        stripe_subscription_id=stripe_subscription_id or "",
+    )
+
+
+def plan_to_dict(plan: SubscriptionPlan | None) -> dict[str, Any] | None:
+    if plan is None:
+        return None
+    return {
+        "slug": plan.slug,
+        "name": plan.name,
+        "description": plan.description,
+        "price_cents": plan.price_cents,
+        "currency": plan.currency,
+        "interval": plan.interval,
+        "is_public": plan.is_public,
+        "is_selectable": plan.is_selectable,
+        "features": {
+            "text_generation": plan.allows_feature("text_generation"),
+            "image_generation": plan.allows_feature("image_generation"),
+            "all_future_features": plan.allows_all_future_features,
+        },
+        "prompt_quota_per_window": plan.prompt_quota_per_window,
+        "prompt_window_hours": plan.prompt_window_hours,
+        "monthly_token_quota": plan.monthly_token_quota,
+        "sort_order": plan.sort_order,
+    }

llm_be/finance/services/quotas.py

@@ -0,0 +1,257 @@
+"""Prompt-window and token-period quota checks (shared by chat + finance APIs)."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from datetime import timedelta
+from typing import Any
+
+from django.db.models import Count, Q, Sum
+from django.utils import timezone
+
+from chat_backend.models import PromptMetric
+from finance.models import UserSubscription
+from finance.services.plans import get_or_create_user_subscription, seed_subscription_plans
+
+
+class QuotaExceeded(Exception):
+    """Raised when a generation turn is blocked by quota."""
+
+    def __init__(self, code: str, message: str, *, details: dict | None = None):
+        super().__init__(message)
+        self.code = code
+        self.message = message
+        self.details = details or {}
+
+
+class FeatureNotAllowed(Exception):
+    """Raised when the user's plan cannot use a feature."""
+
+    def __init__(self, code: str, message: str, *, details: dict | None = None):
+        super().__init__(message)
+        self.code = code
+        self.message = message
+        self.details = details or {}
+
+
+@dataclass
+class UsageSnapshot:
+    prompts_in_window: int
+    prompt_quota: int | None
+    prompts_remaining: int | None
+    window_hours: int
+    tokens_in_period: int | None
+    tokens_out_period: int | None
+    tokens_total_period: int | None
+    turns_missing_token_usage: int
+    monthly_token_quota: int | None
+    tokens_remaining: int | None
+    period_start: Any
+    period_end: Any
+
+    def to_dict(self) -> dict[str, Any]:
+        return {
+            "prompts_in_window": self.prompts_in_window,
+            "prompt_quota": self.prompt_quota,
+            "prompts_remaining": self.prompts_remaining,
+            "window_hours": self.window_hours,
+            "tokens_in_period": self.tokens_in_period,
+            "tokens_out_period": self.tokens_out_period,
+            "tokens_total_period": self.tokens_total_period,
+            "turns_missing_token_usage": self.turns_missing_token_usage,
+            "monthly_token_quota": self.monthly_token_quota,
+            "tokens_remaining": self.tokens_remaining,
+            "period_start": self.period_start.isoformat() if self.period_start else None,
+            "period_end": self.period_end.isoformat() if self.period_end else None,
+        }
+
+
+def _user_conversation_ids(user) -> list[int]:
+    from chat_backend.models import Conversation
+
+    return list(
+        Conversation.objects.filter(user=user, deleted=False).values_list("id", flat=True)
+    )
+
+
+def _billing_period_bounds():
+    """Calendar-month UTC window for token-period aggregation (#17)."""
+    now = timezone.now()
+    start = now.replace(day=1, hour=0, minute=0, second=0, microsecond=0)
+    if start.month == 12:
+        end = start.replace(year=start.year + 1, month=1)
+    else:
+        end = start.replace(month=start.month + 1)
+    return start, end
+
+
+def _sum_tokens(qs) -> tuple[int | None, int | None]:
+    """
+    Sum tokens_in / tokens_out.
+
+    Returns (None, None) when *no* rows reported usage — never fabricate 0.
+    When some rows reported usage, sum only those (nulls ignored by Sum).
+    """
+    agg = qs.aggregate(
+        tin=Sum("tokens_in"),
+        tout=Sum("tokens_out"),
+        with_in=Count("id", filter=Q(tokens_in__isnull=False)),
+        with_out=Count("id", filter=Q(tokens_out__isnull=False)),
+    )
+    tokens_in = agg["tin"] if agg["with_in"] else None
+    tokens_out = agg["tout"] if agg["with_out"] else None
+    return tokens_in, tokens_out
+
+
+def get_usage_snapshot(user) -> UsageSnapshot:
+    seed_subscription_plans(update_existing=False)
+    sub = (
+        UserSubscription.objects.select_related("plan")
+        .filter(user_id=user.pk)
+        .first()
+    )
+    if sub is None:
+        sub = get_or_create_user_subscription(user)
+    plan = sub.plan if sub.is_active else None
+
+    window_hours = plan.prompt_window_hours if plan else 6
+    prompt_quota = plan.prompt_quota_per_window if plan else None
+    monthly_token_quota = sub.effective_monthly_token_quota() if sub.is_active else None
+
+    conversation_ids = _user_conversation_ids(user)
+    now = timezone.now()
+    window_start = now - timedelta(hours=window_hours)
+    period_start, period_end = _billing_period_bounds()
+
+    base = PromptMetric.objects.filter(conversation_id__in=conversation_ids)
+
+    prompts_in_window = base.filter(created__gte=window_start).count()
+    period_qs = base.filter(created__gte=period_start, created__lt=period_end)
+    tokens_in, tokens_out = _sum_tokens(period_qs)
+    missing = period_qs.filter(
+        Q(tokens_in__isnull=True) | Q(tokens_out__isnull=True)
+    ).count()
+
+    if tokens_in is None and tokens_out is None:
+        tokens_total = None
+    else:
+        tokens_total = (tokens_in or 0) + (tokens_out or 0)
+
+    prompts_remaining = None
+    if prompt_quota is not None:
+        prompts_remaining = max(prompt_quota - prompts_in_window, 0)
+
+    tokens_remaining = None
+    if monthly_token_quota is not None and tokens_total is not None:
+        tokens_remaining = max(monthly_token_quota - tokens_total, 0)
+    elif monthly_token_quota is not None and tokens_total is None:
+        # No provider usage yet — do not treat as 0 consumed.
+        tokens_remaining = monthly_token_quota
+
+    return UsageSnapshot(
+        prompts_in_window=prompts_in_window,
+        prompt_quota=prompt_quota,
+        prompts_remaining=prompts_remaining,
+        window_hours=window_hours,
+        tokens_in_period=tokens_in,
+        tokens_out_period=tokens_out,
+        tokens_total_period=tokens_total,
+        turns_missing_token_usage=missing,
+        monthly_token_quota=monthly_token_quota,
+        tokens_remaining=tokens_remaining,
+        period_start=period_start,
+        period_end=period_end,
+    )
+
+
+def assert_feature_allowed(user, feature: str) -> None:
+    from django.conf import settings
+
+    if not getattr(settings, "ENFORCE_SUBSCRIPTION_GATES", True):
+        return
+
+    seed_subscription_plans(update_existing=False)
+    sub = (
+        UserSubscription.objects.select_related("plan")
+        .filter(user_id=user.pk)
+        .first()
+    )
+
+    if sub is None or not sub.is_active or sub.plan is None:
+        raise FeatureNotAllowed(
+            "subscription_required",
+            "An active subscription is required to use this feature.",
+            details={"feature": feature},
+        )
+
+    if not sub.plan.allows_feature(feature):
+        raise FeatureNotAllowed(
+            "feature_not_allowed",
+            f"Your plan ({sub.plan.name}) does not include {feature.replace('_', ' ')}.",
+            details={
+                "feature": feature,
+                "plan": sub.plan.slug,
+            },
+        )
+
+
+def assert_within_quotas(user) -> UsageSnapshot:
+    """
+    Enforce prompt-window (#36) and token-period (#17) limits.
+
+    Precedence: either limit may block. Missing provider token usage does not
+    silently under-count toward a token cap — turns with null tokens are tracked
+    in `turns_missing_token_usage` and token-cap enforcement only uses reported
+    sums; if quota is set and usage is entirely unknown, we allow the turn but
+    surface the gap (callers/admin can tighten later).
+    """
+    seed_subscription_plans(update_existing=False)
+    sub = (
+        UserSubscription.objects.select_related("plan")
+        .filter(user_id=user.pk)
+        .first()
+    )
+
+    if sub is None or not sub.is_active or sub.plan is None:
+        raise QuotaExceeded(
+            "subscription_required",
+            "An active subscription is required before sending prompts.",
+        )
+
+    usage = get_usage_snapshot(user)
+
+    if usage.prompt_quota is not None and usage.prompts_in_window >= usage.prompt_quota:
+        raise QuotaExceeded(
+            "prompt_quota_exceeded",
+            (
+                f"Prompt limit reached ({usage.prompt_quota} per "
+                f"{usage.window_hours} hours). Try again later."
+            ),
+            details=usage.to_dict(),
+        )
+
+    if (
+        usage.monthly_token_quota is not None
+        and usage.tokens_total_period is not None
+        and usage.tokens_total_period >= usage.monthly_token_quota
+    ):
+        raise QuotaExceeded(
+            "token_quota_exceeded",
+            (
+                f"Monthly token limit reached ({usage.monthly_token_quota}). "
+                "Upgrade or wait for the next billing period."
+            ),
+            details=usage.to_dict(),
+        )
+
+    return usage
+
+
+def check_generation_allowed(user, *, feature: str = "text_generation") -> UsageSnapshot:
+    """Combined feature + quota gate for a chat turn."""
+    from django.conf import settings
+
+    if not getattr(settings, "ENFORCE_SUBSCRIPTION_GATES", True):
+        return get_usage_snapshot(user)
+    assert_feature_allowed(user, feature)
+    return assert_within_quotas(user)

llm_be/finance/services/stripe_service.py

@@ -7,7 +7,8 @@ from typing import Any
 import stripe
 from django.conf import settings
 
-from finance.models import Invoice
+from finance.models import Invoice, SubscriptionPlan
+from finance.services.plans import get_plan, seed_subscription_plans
 
 
 class StripeNotConfiguredError(RuntimeError):
@@ -24,21 +25,47 @@ def configure_stripe() -> str:
     return secret
 
 
-def subscription_line_items() -> list[dict[str, Any]]:
-    """Build Checkout line_items from settings-backed subscription pricing."""
-    price_id = settings.STRIPE_PRICE_ID
+def resolve_checkout_plan(plan_slug: str | None = None) -> SubscriptionPlan:
+    """Return the plan for Checkout (defaults to public Founders)."""
+    seed_subscription_plans(update_existing=False)
+    slug = (plan_slug or SubscriptionPlan.Slug.FOUNDERS).strip().lower()
+    plan = get_plan(slug)
+    if plan is None:
+        raise ValueError(f"Unknown plan: {slug}")
+    if not plan.is_selectable:
+        raise ValueError(f"Plan '{plan.slug}' is not available for checkout.")
+    return plan
+
+
+def subscription_line_items(plan: SubscriptionPlan) -> list[dict[str, Any]]:
+    """Build Checkout line_items from a SubscriptionPlan (or legacy settings)."""
+    price_id = (plan.stripe_price_id or "").strip() or (
+        settings.STRIPE_PRICE_ID if plan.slug == SubscriptionPlan.Slug.FOUNDERS else ""
+    )
     if price_id:
         return [{"price": price_id, "quantity": 1}]
 
+    # Founders without a plan stripe_price_id may still use legacy env amount.
+    unit_amount = plan.price_cents
+    product_name = plan.name
+    currency = plan.currency or settings.SUBSCRIPTION_PRICE_CURRENCY
+    interval = plan.interval or settings.SUBSCRIPTION_PRICE_INTERVAL
+    if plan.slug == SubscriptionPlan.Slug.FOUNDERS and not plan.stripe_price_id:
+        # Keep env overrides working for the live Founders price.
+        unit_amount = int(
+            getattr(settings, "SUBSCRIPTION_PRICE_AMOUNT_CENTS", None) or unit_amount
+        )
+        product_name = (
+            getattr(settings, "SUBSCRIPTION_PRODUCT_NAME", None) or product_name
+        )
+
     return [
         {
             "price_data": {
-                "currency": settings.SUBSCRIPTION_PRICE_CURRENCY,
-                "unit_amount": settings.SUBSCRIPTION_PRICE_AMOUNT_CENTS,
-                "recurring": {"interval": settings.SUBSCRIPTION_PRICE_INTERVAL},
-                "product_data": {
-                    "name": settings.SUBSCRIPTION_PRODUCT_NAME,
-                },
+                "currency": currency,
+                "unit_amount": unit_amount,
+                "recurring": {"interval": interval},
+                "product_data": {"name": product_name},
             },
             "quantity": 1,
         }
@@ -50,19 +77,22 @@ def create_checkout_session(
     user,
     success_url: str | None = None,
     cancel_url: str | None = None,
+    plan_slug: str | None = None,
 ):
-    """Create a Stripe Checkout Session for the subscription plan."""
+    """Create a Stripe Checkout Session for a selectable subscription plan."""
     configure_stripe()
+    plan = resolve_checkout_plan(plan_slug)
 
     metadata = {
         "user_id": str(user.pk),
         "company_id": str(user.company_id) if user.company_id else "",
+        "plan_slug": plan.slug,
     }
     customer_email = getattr(user, "email", None) or None
 
     session = stripe.checkout.Session.create(
         mode="subscription",
-        line_items=subscription_line_items(),
+        line_items=subscription_line_items(plan),
         success_url=success_url or settings.STRIPE_CHECKOUT_SUCCESS_URL,
         cancel_url=cancel_url or settings.STRIPE_CHECKOUT_CANCEL_URL,
         customer_email=customer_email,
@@ -70,7 +100,7 @@ def create_checkout_session(
         metadata=metadata,
         subscription_data={"metadata": metadata},
     )
-    return session
+    return session, plan
 
 
 def resolve_stripe_customer_id(*, user) -> str | None:

llm_be/finance/services/webhooks.py

@@ -11,6 +11,7 @@ from django.db import transaction
 from django.utils import timezone
 
 from finance.models import Invoice, Payment
+from finance.services.plans import assign_founders_from_stripe
 
 logger = logging.getLogger(__name__)
 User = get_user_model()
@@ -211,6 +212,11 @@ def handle_checkout_session_completed(session: dict[str, Any]) -> Invoice | None
             ),
             paid_at=timezone.now(),
         )
+    if session.get("payment_status") == "paid" or session.get("subscription"):
+        assign_founders_from_stripe(
+            user,
+            stripe_subscription_id=session.get("subscription") or "",
+        )
     return invoice
 
 
@@ -270,6 +276,10 @@ def handle_invoice_paid(stripe_invoice: dict[str, Any]) -> Invoice | None:
             stripe_charge_id=charge if isinstance(charge, str) else None,
             paid_at=paid_at,
         )
+    assign_founders_from_stripe(
+        user,
+        stripe_subscription_id=stripe_invoice.get("subscription") or "",
+    )
     return invoice
 
 

llm_be/finance/signals.py

@@ -0,0 +1,8 @@
+"""Finance app signals."""
+
+
+def seed_plans_on_migrate(sender, **kwargs):
+    """Ensure the subscription catalog exists after migrate."""
+    from finance.services.plans import seed_subscription_plans
+
+    seed_subscription_plans(update_existing=False)

llm_be/finance/tests/test_plans_quotas.py

@@ -0,0 +1,261 @@
+"""Tests for multi-plan catalog, Backer whitelist, quotas, and subscription API."""
+
+from datetime import timedelta
+from unittest.mock import MagicMock, patch
+
+from django.test import TestCase, override_settings
+from django.urls import reverse
+from django.utils import timezone
+from rest_framework import status
+from rest_framework.test import APITestCase
+
+from chat_backend.models import PromptMetric
+from chat_backend.tests.factories import make_company, make_conversation, make_user
+from finance.models import BackerEmail, SubscriptionPlan, UserSubscription
+from finance.services.plans import (
+    assign_plan,
+    needs_checkout,
+    seed_subscription_plans,
+    try_redeem_backer_email,
+)
+from finance.services.quotas import (
+    FeatureNotAllowed,
+    QuotaExceeded,
+    assert_feature_allowed,
+    assert_within_quotas,
+    get_usage_snapshot,
+)
+
+
+class PlanCatalogTestCase(TestCase):
+    def test_seed_creates_expected_plans(self):
+        plans = {p.slug: p for p in seed_subscription_plans()}
+        self.assertEqual(
+            set(plans),
+            {"founders", "standard", "pro", "business", "backer"},
+        )
+        self.assertTrue(plans["founders"].is_public)
+        self.assertTrue(plans["founders"].is_selectable)
+        self.assertEqual(plans["founders"].price_cents, 1000)
+        self.assertEqual(plans["founders"].prompt_quota_per_window, 300)
+
+        self.assertFalse(plans["standard"].is_public)
+        self.assertEqual(plans["standard"].price_cents, 1500)
+        self.assertEqual(plans["standard"].prompt_quota_per_window, 100)
+        self.assertFalse(plans["standard"].allows_image_generation)
+
+        self.assertEqual(plans["pro"].price_cents, 4000)
+        self.assertEqual(plans["pro"].prompt_quota_per_window, 200)
+        self.assertTrue(plans["pro"].allows_image_generation)
+
+        self.assertEqual(plans["business"].price_cents, 9900)
+        self.assertEqual(plans["business"].prompt_quota_per_window, 300)
+
+        self.assertEqual(plans["backer"].price_cents, 0)
+        self.assertFalse(plans["backer"].is_selectable)
+        self.assertTrue(plans["backer"].allows_all_future_features)
+
+
+class BackerRedeemTestCase(TestCase):
+    def setUp(self):
+        seed_subscription_plans()
+        self.company = make_company()
+
+    def test_redeem_assigns_backer_and_skips_checkout(self):
+        BackerEmail.objects.create(email="backer@example.com")
+        user = make_user(email="backer@example.com", company=self.company)
+        sub = try_redeem_backer_email(user)
+        self.assertIsNotNone(sub)
+        self.assertEqual(sub.plan.slug, "backer")
+        self.assertEqual(sub.source, UserSubscription.Source.BACKER)
+        self.assertFalse(needs_checkout(user))
+        entry = BackerEmail.objects.get(email="backer@example.com")
+        self.assertIsNotNone(entry.redeemed_at)
+        self.assertEqual(entry.redeemed_user_id, user.pk)
+
+    def test_redeem_is_one_shot(self):
+        BackerEmail.objects.create(email="once@example.com")
+        user = make_user(email="once@example.com", company=self.company)
+        self.assertIsNotNone(try_redeem_backer_email(user))
+        self.assertIsNone(try_redeem_backer_email(user))
+
+
+@override_settings(ENFORCE_SUBSCRIPTION_GATES=True)
+class QuotaGateTestCase(TestCase):
+    def setUp(self):
+        seed_subscription_plans()
+        self.company = make_company()
+        self.user = make_user(company=self.company)
+        self.plan = SubscriptionPlan.objects.get(slug="standard")
+        assign_plan(
+            self.user,
+            plan=self.plan,
+            source=UserSubscription.Source.ADMIN,
+        )
+        self.conversation = make_conversation(user=self.user)
+
+    def _add_metrics(self, count, *, tokens_in=None, tokens_out=None):
+        now = timezone.now()
+        for i in range(count):
+            PromptMetric.objects.create(
+                prompt_id=1000 + i,
+                conversation_id=self.conversation.id,
+                start_time=now,
+                prompt_length=10,
+                tokens_in=tokens_in,
+                tokens_out=tokens_out,
+                has_file=False,
+                model_name="test",
+            )
+
+    def test_prompt_quota_blocks(self):
+        self._add_metrics(100)
+        with self.assertRaises(QuotaExceeded) as ctx:
+            assert_within_quotas(self.user)
+        self.assertEqual(ctx.exception.code, "prompt_quota_exceeded")
+
+    def test_feature_gate_blocks_image_on_standard(self):
+        with self.assertRaises(FeatureNotAllowed) as ctx:
+            assert_feature_allowed(self.user, "image_generation")
+        self.assertEqual(ctx.exception.code, "feature_not_allowed")
+
+    def test_pro_allows_image(self):
+        pro = SubscriptionPlan.objects.get(slug="pro")
+        assign_plan(
+            self.user, plan=pro, source=UserSubscription.Source.ADMIN
+        )
+        assert_feature_allowed(self.user, "image_generation")
+
+    def test_token_quota_blocks_when_reported(self):
+        self.plan.monthly_token_quota = 50
+        self.plan.prompt_quota_per_window = 1000
+        self.plan.save()
+        self._add_metrics(1, tokens_in=30, tokens_out=30)
+        with self.assertRaises(QuotaExceeded) as ctx:
+            assert_within_quotas(self.user)
+        self.assertEqual(ctx.exception.code, "token_quota_exceeded")
+
+    def test_null_tokens_do_not_fabricate_zero_usage(self):
+        self._add_metrics(3, tokens_in=None, tokens_out=None)
+        usage = get_usage_snapshot(self.user)
+        self.assertIsNone(usage.tokens_in_period)
+        self.assertIsNone(usage.tokens_out_period)
+        self.assertIsNone(usage.tokens_total_period)
+        self.assertGreaterEqual(usage.turns_missing_token_usage, 3)
+
+
+class PlanListAndSubscriptionApiTestCase(APITestCase):
+    def setUp(self):
+        seed_subscription_plans()
+        self.company = make_company()
+        self.user = make_user(company=self.company)
+
+    def test_public_plans_only_founders(self):
+        url = reverse("finance_plans")
+        response = self.client.get(url)
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        slugs = [row["slug"] for row in response.data]
+        self.assertEqual(slugs, ["founders"])
+
+    def test_subscription_me_includes_usage_nulls(self):
+        self.client.force_authenticate(user=self.user)
+        founders = SubscriptionPlan.objects.get(slug="founders")
+        assign_plan(
+            self.user,
+            plan=founders,
+            source=UserSubscription.Source.STRIPE,
+        )
+        url = reverse("finance_subscription_me")
+        response = self.client.get(url)
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        self.assertEqual(response.data["plan"]["slug"], "founders")
+        self.assertFalse(response.data["needs_checkout"])
+        self.assertIsNone(response.data["usage"]["tokens_in_period"])
+        self.assertEqual(response.data["usage"]["prompt_quota"], 300)
+
+
+class CheckoutUsesFoundersPlanTestCase(APITestCase):
+    def setUp(self):
+        seed_subscription_plans()
+        self.company = make_company()
+        self.user = make_user(company=self.company)
+        self.client.force_authenticate(user=self.user)
+        self.url = reverse("finance_checkout")
+
+    @override_settings(
+        STRIPE_SECRET_KEY="sk_test_fake",
+        SUBSCRIPTION_PRICE_AMOUNT_CENTS=1000,
+        SUBSCRIPTION_PRICE_CURRENCY="usd",
+        SUBSCRIPTION_PRICE_INTERVAL="month",
+        SUBSCRIPTION_PRODUCT_NAME="Founders",
+        STRIPE_PRICE_ID="",
+        STRIPE_CHECKOUT_SUCCESS_URL="http://localhost:3000/ok",
+        STRIPE_CHECKOUT_CANCEL_URL="http://localhost:3000/cancel",
+    )
+    @patch("finance.services.stripe_service.stripe.checkout.Session.create")
+    def test_checkout_defaults_to_founders(self, mock_create):
+        mock_session = MagicMock()
+        mock_session.id = "cs_test_founders"
+        mock_session.url = "https://checkout.stripe.com/c/pay/cs_test_founders"
+        mock_session.customer = None
+        mock_create.return_value = mock_session
+
+        response = self.client.post(self.url, {}, format="json")
+        self.assertEqual(response.status_code, status.HTTP_201_CREATED)
+        self.assertEqual(response.data["plan_slug"], "founders")
+        kwargs = mock_create.call_args.kwargs
+        self.assertEqual(kwargs["metadata"]["plan_slug"], "founders")
+        self.assertEqual(
+            kwargs["line_items"][0]["price_data"]["unit_amount"], 1000
+        )
+
+    def test_backer_cannot_checkout(self):
+        backer = SubscriptionPlan.objects.get(slug="backer")
+        assign_plan(
+            self.user, plan=backer, source=UserSubscription.Source.BACKER
+        )
+        response = self.client.post(self.url, {}, format="json")
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+        self.assertFalse(response.data["needs_checkout"])
+
+
+class TokenSerializerApiTestCase(APITestCase):
+    def setUp(self):
+        self.company = make_company()
+        self.user = make_user(company=self.company)
+        self.client.force_authenticate(user=self.user)
+        self.conversation = make_conversation(user=self.user, title="Tok")
+
+    def test_conversation_tokens_null_when_unreported(self):
+        PromptMetric.objects.create(
+            prompt_id=1,
+            conversation_id=self.conversation.id,
+            start_time=timezone.now(),
+            prompt_length=5,
+            tokens_in=None,
+            tokens_out=None,
+            has_file=False,
+            model_name="t",
+        )
+        response = self.client.get(reverse("conversations"))
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        row = next(r for r in response.data if r["id"] == self.conversation.id)
+        self.assertIsNone(row["tokens_in"])
+        self.assertIsNone(row["tokens_out"])
+
+    def test_conversation_tokens_sum_when_reported(self):
+        for tin, tout, pid in ((10, 20, 1), (5, None, 2), (None, 7, 3)):
+            PromptMetric.objects.create(
+                prompt_id=pid,
+                conversation_id=self.conversation.id,
+                start_time=timezone.now(),
+                prompt_length=5,
+                tokens_in=tin,
+                tokens_out=tout,
+                has_file=False,
+                model_name="t",
+            )
+        response = self.client.get(reverse("conversations"))
+        row = next(r for r in response.data if r["id"] == self.conversation.id)
+        self.assertEqual(row["tokens_in"], 15)
+        self.assertEqual(row["tokens_out"], 27)

llm_be/finance/urls.py

@@ -5,7 +5,9 @@ from finance.views import (
     CreateCheckoutSessionView,
     InvoiceListView,
     PaymentListView,
+    PlanListView,
     StripeWebhookView,
+    SubscriptionMeView,
 )
 
 urlpatterns = [
@@ -29,6 +31,16 @@ urlpatterns = [
         PaymentListView.as_view(),
         name="finance_payments",
     ),
+    path(
+        "plans/",
+        PlanListView.as_view(),
+        name="finance_plans",
+    ),
+    path(
+        "subscription/",
+        SubscriptionMeView.as_view(),
+        name="finance_subscription_me",
+    ),
     path(
         "webhooks/stripe/",
         StripeWebhookView.as_view(),

llm_be/finance/views.py

@@ -6,13 +6,20 @@ from rest_framework import permissions, status
 from rest_framework.response import Response
 from rest_framework.views import APIView
 
-from finance.models import Invoice, Payment
+from finance.models import Invoice, Payment, SubscriptionPlan, UserSubscription
 from finance.serializers import (
     CheckoutSessionSerializer,
     InvoiceSerializer,
     PaymentSerializer,
     PortalSessionSerializer,
+    SubscriptionPlanSerializer,
 )
+from finance.services.plans import (
+    needs_checkout,
+    plan_to_dict,
+    seed_subscription_plans,
+)
+from finance.services.quotas import get_usage_snapshot
 from finance.services.stripe_service import (
     StripeNotConfiguredError,
     create_billing_portal_session,
@@ -32,11 +39,34 @@ class CreateCheckoutSessionView(APIView):
         serializer.is_valid(raise_exception=True)
 
         try:
-            session = create_checkout_session(
+            sub = request.user.subscription
+        except UserSubscription.DoesNotExist:
+            sub = None
+        if (
+            sub is not None
+            and sub.is_active
+            and sub.source == UserSubscription.Source.BACKER
+        ):
+            return Response(
+                {
+                    "detail": (
+                        "This account has complimentary Backer access and "
+                        "does not require payment."
+                    ),
+                    "needs_checkout": False,
+                },
+                status=status.HTTP_400_BAD_REQUEST,
+            )
+
+        try:
+            session, plan = create_checkout_session(
                 user=request.user,
                 success_url=serializer.validated_data.get("success_url"),
                 cancel_url=serializer.validated_data.get("cancel_url"),
+                plan_slug=serializer.validated_data.get("plan_slug"),
             )
+        except ValueError as exc:
+            return Response({"detail": str(exc)}, status=status.HTTP_400_BAD_REQUEST)
         except StripeNotConfiguredError as exc:
             return Response(
                 {"detail": str(exc)},
@@ -58,11 +88,11 @@ class CreateCheckoutSessionView(APIView):
                 "company": request.user.company,
                 "provider": Invoice.Provider.STRIPE,
                 "status": Invoice.Status.OPEN,
-                "currency": settings.SUBSCRIPTION_PRICE_CURRENCY,
-                "amount_due": settings.SUBSCRIPTION_PRICE_AMOUNT_CENTS,
+                "currency": plan.currency or settings.SUBSCRIPTION_PRICE_CURRENCY,
+                "amount_due": plan.price_cents,
                 "amount_paid": 0,
                 "stripe_customer_id": getattr(session, "customer", None) or "",
-                "description": settings.SUBSCRIPTION_PRODUCT_NAME,
+                "description": plan.name,
             },
         )
 
@@ -70,6 +100,7 @@ class CreateCheckoutSessionView(APIView):
             {
                 "checkout_url": session.url,
                 "session_id": session.id,
+                "plan_slug": plan.slug,
             },
             status=status.HTTP_201_CREATED,
         )
@@ -129,6 +160,50 @@ class PaymentListView(APIView):
         return Response(PaymentSerializer(payments, many=True).data)
 
 
+class PlanListView(APIView):
+    """Public-facing plan catalog (only `is_public` rows by default)."""
+
+    permission_classes = (permissions.AllowAny,)
+    authentication_classes = ()
+
+    def get(self, request):
+        seed_subscription_plans(update_existing=False)
+        include_all = (
+            request.user
+            and request.user.is_authenticated
+            and request.user.is_staff
+            and request.query_params.get("all") == "1"
+        )
+        qs = SubscriptionPlan.objects.all()
+        if not include_all:
+            qs = qs.filter(is_public=True)
+        return Response(SubscriptionPlanSerializer(qs, many=True).data)
+
+
+class SubscriptionMeView(APIView):
+    """Current user's plan, checkout need, and usage snapshot (#16/#17/#36)."""
+
+    def get(self, request):
+        seed_subscription_plans(update_existing=False)
+        try:
+            sub = request.user.subscription
+        except UserSubscription.DoesNotExist:
+            sub = None
+
+        usage = get_usage_snapshot(request.user)
+        payload = {
+            "plan": plan_to_dict(sub.plan) if sub and sub.plan_id else None,
+            "status": sub.status if sub else UserSubscription.Status.NONE,
+            "source": sub.source if sub else UserSubscription.Source.NONE,
+            "needs_checkout": needs_checkout(request.user),
+            "stripe_subscription_id": (
+                sub.stripe_subscription_id if sub else ""
+            ),
+            "usage": usage.to_dict(),
+        }
+        return Response(payload)
+
+
 class StripeWebhookView(APIView):
     """Verify Stripe signatures and upsert local invoice/payment rows."""
 

llm_be/llm_be/settings.py

@@ -172,7 +172,7 @@ INSTALLED_APPS = [
     "whitenoise.runserver_nostatic",
     "django.contrib.staticfiles",
     "chat_backend",
-    "finance",
+    "finance.apps.FinanceConfig",
     "rest_framework",
     "corsheaders",
     "rest_framework_simplejwt.token_blacklist",
@@ -307,6 +307,8 @@ os.makedirs(directory_path, exist_ok=True)
 
 ALLOW_IMAGE_GENERATION = env_bool("ALLOW_IMAGE_GENERATION", False)
 ALLOW_INTERNET_ACCESS = env_bool("ALLOW_INTERNET_ACCESS", True)
+# When True, chat turns require an active plan and respect prompt/token quotas.
+ENFORCE_SUBSCRIPTION_GATES = env_bool("ENFORCE_SUBSCRIPTION_GATES", True)
 
 # Self-serve account registration (sign-up page). Default off — enable via
 # control-node secret (chat_backend_<env>.env) when ready for public sign-up.
@@ -346,7 +348,7 @@ SUBSCRIPTION_PRICE_INTERVAL = (
     env("SUBSCRIPTION_PRICE_INTERVAL", "month") or "month"
 ).lower()
 SUBSCRIPTION_PRODUCT_NAME = (
-    env("SUBSCRIPTION_PRODUCT_NAME", "Chat Subscription") or "Chat Subscription"
+    env("SUBSCRIPTION_PRODUCT_NAME", "Founders") or "Founders"
 )
 
 FRONTEND_BASE_URL = (

llm_be/llm_be/test_runner.py

@@ -18,3 +18,5 @@ class ChatBackendTestRunner(DiscoverRunner):
         os.environ.setdefault("SKIP_RAG_INIT", "1")
         super().setup_test_environment(**kwargs)
         settings.PASSWORD_HASHERS = ["django.contrib.auth.hashers.MD5PasswordHasher"]
+        # Opt-in for plan/quota tests via @override_settings.
+        settings.ENFORCE_SUBSCRIPTION_GATES = False