feat(dev-plans): charge full price on tier upgrade

Replace prorated tier-change billing with a full-charge, fresh-cycle
model for DevPass and Chat plan upgrades.

On an upgrade we now update the Stripe subscription with
`billing_cycle_anchor: "now"` + `proration_behavior: "none"` +
`payment_behavior: "error_if_incomplete"`, so Stripe immediately charges
the full new-tier price, starts a fresh billing period, and applies no
proration. Credits reset to the new tier's full allowance with usage
zeroed. This removes the custom prorated-invoice + manual-rollback dance
and the prorated credit-delta math.

Downgrades are unchanged (DevPass deferred to renewal; Chat immediate).

- dev-plans: full-charge upgrade, full-reset credits, keep per-cycle
  claim as a double-charge guard; preview returns full price + full
  new-tier credits.
- stripe webhook: tier-change invoice (subscription_update) now full-
  resets to the new tier (read from subscription metadata), idempotent
  via unique stripeInvoiceId; add a chat-subscription skip branch so a
  chat subscription_update invoice never flips the org to Pro.
- chat-plans: mirror the upgrade model; record the invoice id.
- remove now-unused getProratedCreditDelta; update tests + UI copy.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: steebchen

apps/api/src/routes/chat-plans.ts

@@ -431,58 +431,75 @@ chatPlans.openapi(changeTier, async (c) => {
 		const subscription = await getStripe().subscriptions.retrieve(
 			personalOrg.chatPlanStripeSubscriptionId,
 		);
+		const subscriptionItemId = subscription.items.data[0].id;
+		const newCreditsLimit = getChatPlanCreditsLimit(newTier);
 
-		// Same payment-behavior strategy as dev-plans: charge prorated upgrades
-		// synchronously and reject the upgrade if the card declines, so we don't
-		// leave the customer on the higher tier without collecting.
-		const updated = await getStripe().subscriptions.update(
-			personalOrg.chatPlanStripeSubscriptionId,
-			{
-				items: [
-					{
-						id: subscription.items.data[0].id,
-						price: newPriceId,
+		if (isUpgrade) {
+			// Charge the full new-tier price today and start a fresh billing cycle
+			// (`billing_cycle_anchor: "now"`) with no proration
+			// (`proration_behavior: "none"`). `error_if_incomplete` makes the update
+			// atomic, so a declined card leaves the subscription on the old tier.
+			const updated = await getStripe().subscriptions.update(
+				personalOrg.chatPlanStripeSubscriptionId,
+				{
+					items: [{ id: subscriptionItemId, price: newPriceId }],
+					proration_behavior: "none",
+					billing_cycle_anchor: "now",
+					payment_behavior: "error_if_incomplete",
+					metadata: {
+						...subscription.metadata,
+						chatPlan: newTier,
+						chatPlanCycle: "monthly",
 					},
-				],
-				proration_behavior: isUpgrade ? "always_invoice" : "create_prorations",
-				payment_behavior: isUpgrade
-					? "error_if_incomplete"
-					: "allow_incomplete",
-				metadata: {
-					...subscription.metadata,
+				},
+			);
+
+			if (updated.status !== "active" && updated.status !== "trialing") {
+				throw new HTTPException(402, {
+					message:
+						"Upgrade payment could not be collected. Update your payment method and try again.",
+				});
+			}
+
+			// Fresh billing cycle: reset credits to the new tier's full allowance,
+			// zero out usage, and advance the cycle start. The resulting
+			// `subscription_update` invoice is recorded and emailed by the webhook
+			// (handleInvoicePaymentSucceeded), keyed on its unique stripeInvoiceId, so
+			// we don't insert an upgrade transaction here.
+			await db
+				.update(tables.organization)
+				.set({
 					chatPlan: newTier,
-					chatPlanCycle: "monthly",
+					chatPlanCreditsLimit: newCreditsLimit.toString(),
+					chatPlanCreditsUsed: "0",
+					chatPlanBillingCycleStart: new Date(),
+				})
+				.where(eq(tables.organization.id, personalOrg.id));
+		} else {
+			// Downgrade: unchanged behavior. Take effect immediately with Stripe
+			// proration crediting the unused higher-tier time on the next invoice.
+			await getStripe().subscriptions.update(
+				personalOrg.chatPlanStripeSubscriptionId,
+				{
+					items: [{ id: subscriptionItemId, price: newPriceId }],
+					proration_behavior: "create_prorations",
+					payment_behavior: "allow_incomplete",
+					metadata: {
+						...subscription.metadata,
+						chatPlan: newTier,
+						chatPlanCycle: "monthly",
+					},
 				},
-			},
-		);
+			);
 
-		if (
-			isUpgrade &&
-			updated.status !== "active" &&
-			updated.status !== "trialing"
-		) {
-			throw new HTTPException(402, {
-				message:
-					"Upgrade payment could not be collected. Update your payment method and try again.",
-			});
-		}
-
-		const newCreditsLimit = getChatPlanCreditsLimit(newTier);
+			await db
+				.update(tables.organization)
+				.set({
+					chatPlan: newTier,
+					chatPlanCreditsLimit: newCreditsLimit.toString(),
+				})
+				.where(eq(tables.organization.id, personalOrg.id));
 
-		await db
-			.update(tables.organization)
-			.set({
-				chatPlan: newTier,
-				chatPlanCreditsLimit: newCreditsLimit.toString(),
-			})
-			.where(eq(tables.organization.id, personalOrg.id));
-
-		// Upgrades charge a prorated amount (`always_invoice`); the resulting
-		// `subscription_update` invoice is recorded and emailed by the webhook
-		// (handleInvoicePaymentSucceeded), keyed on its unique stripeInvoiceId, so
-		// we must not insert a duplicate upgrade transaction here. Downgrades issue
-		// no charge/invoice, so record the tier change now.
-		if (!isUpgrade) {
 			await db.insert(tables.transaction).values({
 				organizationId: personalOrg.id,
 				type: "chat_plan_downgrade",