fix(billing): add customer portal helper, benefits access, and Polar scaffold docs (#2)

_template_options/payments/_polar/README.md

@@ -2,30 +2,47 @@
 
 Use this when the product should sell through Polar checkout sessions and later map orders, subscriptions, or benefits into app entitlements.
 
+## Installation
+
 Install only if selected:
 
 ```sh
 bun add @polar-sh/sdk
 ```
 
-Environment:
+## Environment Variables
+
+Server-side only (`.env` / server runtime):
 
 ```env
-POLAR_ACCESS_TOKEN=
-POLAR_SERVER=sandbox
-POLAR_PRODUCT_PRO=
+POLAR_ACCESS_TOKEN=polar_at_...
+POLAR_SERVER=sandbox # 'sandbox' | 'production'
+POLAR_PRODUCT_PRO=prod_...
 ```
 
-Activation checklist:
+## When to Choose Polar vs Autumn / Stripe Direct
+
+- **Choose Polar** when you want an open-source Merchant of Record (MoR) / developer-centric monetization platform that handles EU VAT / global sales tax, built-in customer portals, and automatic benefits distribution (e.g. GitHub repository access, Discord role grants, file downloads, license keys).
+- **Choose Autumn** when you want lightweight usage-based metering tightly integrated with Convex and direct Stripe accounts.
+- **Choose Stripe Direct** when you have custom Stripe Elements requirements, specific marketplace payout flows, or existing Stripe Connect infrastructure.
+
+## Customer Portal & Benefits Access
+
+- **Customer Portal**: Polar provides a hosted customer portal out of the box. Use `createCustomerPortalSession` to generate a direct management URL for customers to manage subscriptions, update payment methods, and download invoices.
+- **Entitlements & Benefits**: Polar supports automated benefit grants (GitHub repository invites, Discord roles, digital file downloads). Entitlements can be queried via Polar API or synced via `order.created` / `subscription.active` webhooks.
+
+## Activation Checklist
 
 1. Copy `billing-adapter.ts.example` to `src/lib/server/billing/provider.ts`.
 2. Keep `POLAR_ACCESS_TOKEN` server-side only.
-3. Create checkout sessions from server routes or Convex actions, never from client components.
+3. Create checkout sessions and customer portal sessions from server routes or Convex actions, never from client components.
 4. Store `external_customer_id` as the app user ID.
-5. Add webhook handling before granting paid access.
+5. Add webhook handling (`/api/webhooks/polar`) before granting paid access.
 6. Remove Autumn or other billing providers after Polar checkout and entitlement sync work.
 
-Official docs checked while creating this scaffold:
+## References
 
-- Polar API overview: https://polar.sh/docs/api-reference/introduction
-- Polar create Checkout Session: https://polar.sh/docs/api-reference/checkouts/create-session
+- Polar API Overview: https://polar.sh/docs/api-reference/introduction
+- Polar Create Checkout Session: https://polar.sh/docs/api-reference/checkouts/create-session
+- Polar Customer Portal: https://polar.sh/docs/api-reference/customer-portal
+- Polar Webhooks: https://polar.sh/docs/api-reference/webhooks

_template_options/payments/_polar/billing-adapter.ts.example

@@ -67,3 +67,25 @@ export async function createCheckoutSession(
 		checkoutUrl: checkout.url
 	};
 }
+
+export async function createCustomerPortalSession(
+	customerId: string,
+	env: PolarBillingEnv
+): Promise<string> {
+	const response = await fetch(`${getPolarBaseUrl(env.POLAR_SERVER)}/customer-portal/customers/${customerId}/session`, {
+		method: 'POST',
+		headers: {
+			Authorization: `Bearer ${env.POLAR_ACCESS_TOKEN}`,
+			'Content-Type': 'application/json',
+			Accept: 'application/json'
+		}
+	});
+
+	const data = (await response.json()) as { url?: string; detail?: string };
+	if (!response.ok || !data.url) {
+		throw new Error(data.detail ?? 'Failed to create Polar customer portal session');
+	}
+
+	return data.url;
+}
+