feat(billing): add GET /billing/state aggregating subscription + plan + features

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/app/services/billing.py

@@ -105,6 +105,61 @@ class BillingService:
         )
         return session.url
 
+    @staticmethod
+    async def get_billing_state(db: AsyncSession, account):
+        """Aggregate Subscription + PlanLimits + PlanBilling + resolved feature
+        flags for the account."""
+        from app.models.plan_limits import PlanLimits
+        from app.models.plan_billing import PlanBilling
+        from app.models.feature_flag import (
+            FeatureFlag, PlanFeatureDefault, AccountFeatureOverride,
+        )
+
+        sub = (await db.execute(
+            select(Subscription).where(Subscription.account_id == account.id)
+        )).scalar_one_or_none()
+        if sub is None:
+            from fastapi import HTTPException
+            raise HTTPException(status_code=404, detail="No subscription for account")
+
+        pl = (await db.execute(
+            select(PlanLimits).where(PlanLimits.plan == sub.plan)
+        )).scalar_one_or_none()
+        pb = (await db.execute(
+            select(PlanBilling).where(PlanBilling.plan == sub.plan)
+        )).scalar_one_or_none()
+
+        # Resolved feature flags: plan defaults overridden by account overrides
+        defaults = (await db.execute(
+            select(PlanFeatureDefault, FeatureFlag)
+            .join(FeatureFlag, PlanFeatureDefault.flag_id == FeatureFlag.id)
+            .where(PlanFeatureDefault.plan == sub.plan)
+        )).all()
+        resolved = {flag.flag_key: pfd.enabled for pfd, flag in defaults}
+        overrides = (await db.execute(
+            select(AccountFeatureOverride, FeatureFlag)
+            .join(FeatureFlag, AccountFeatureOverride.flag_id == FeatureFlag.id)
+            .where(AccountFeatureOverride.account_id == account.id)
+        )).all()
+        for ovr, flag in overrides:
+            resolved[flag.flag_key] = ovr.enabled
+
+        return {
+            "subscription": {
+                "status": sub.status,
+                "plan": sub.plan,
+                "current_period_start": sub.current_period_start,
+                "current_period_end": sub.current_period_end,
+                "cancel_at_period_end": sub.cancel_at_period_end,
+                "seat_limit": sub.seat_limit,
+                "has_pro_entitlement": sub.has_pro_entitlement,
+                "is_paid": sub.is_paid,
+            },
+            "plan_billing": pb,
+            "plan_limits": _plan_limits_to_dict(pl) if pl else {},
+            "enabled_features": resolved,
+        }
+
     @staticmethod
     async def apply_subscription_event(
         db: AsyncSession, event_id: str, event_type: str, payload: dict
@@ -136,6 +191,10 @@ class BillingService:
         return True
 
 
+def _plan_limits_to_dict(pl) -> dict:
+    return {c.name: getattr(pl, c.name) for c in pl.__table__.columns}
+
+
 def _excerpt(payload: dict) -> dict:
     obj = payload.get("data", {}).get("object", {})
     return {