fix(billing): resolve plan via priceId map, not price.metadata.planId (#3742)

Port trawl's #1250 fix upstream: `customer.subscription.updated` was reading
`price.metadata.planId` which is empty in real Stripe webhook payloads (planId
lives on the Product, not the Price). Every paid org's plan was silently reset
to `free` on every Stripe subscription update event.

Fix:
- Add `buildPriceIdToPlanMap()` — builds `Map<priceId, planName>` from
  `config.stripe.prices` at boot (monthly + annual per plan)
- Rewrite `resolvePlan()` — looks up plan via priceId map first; falls back to
  `price.metadata.planId` for legacy test fixtures; final fallback `free` + warn
- Sync `cancelAt`/`cancelAtPeriodEnd` on `customer.subscription.updated` — writes
  the fields added by #3741 so the UI can show pending cancellation dates
- Use priceId map in `previousPlan` detection (plan change block in updated handler)
- Strip trawl-specific `analytics.capture('subscription_changed')` calls (not ported)

Also ports `retryWithBackoff` + `isNonTransientStripeError` patterns (already
in devkit from a prior PR — kept identical to trawl).

Adds 20 unit tests covering: priceId map resolution, annual/monthly variants,
unknown priceId fallback to free, legacy metadata fallback, priority of map over
metadata, cancelAt unix→Date conversion, null cancel clear, absent field guard,
handleSubscriptionCreated race safety (E11000 idempotency), and Dashboard
subscription creation path.

Closes #3742

Author: PierreBrisorgueil

modules/billing/services/billing.webhook.service.js

@@ -57,17 +57,45 @@ const validatePlan = (plan) => {
  */
 const planRanks = Object.fromEntries((config.billing?.plans || []).map((p, i) => [p, i]));
 
+/**
+ * Reverse-map from Stripe price ID → plan name, built from config.stripe.prices at boot.
+ * config.stripe.prices = { growth: { monthly: 'price_xxx', annual: 'price_yyy' }, pro: { ... } }
+ * This avoids relying on price.metadata.planId (empty on Stripe webhook payloads — planId
+ * lives on the Product, not the Price) and avoids a Stripe API call per webhook.
+ *
+ * Fix: resolvePlan no longer reads price.metadata (always empty in real Stripe webhook payloads).
+ */
+const buildPriceIdToPlanMap = () => {
+  const map = {};
+  const stripePrices = config.stripe?.prices || {};
+  for (const [planId, intervals] of Object.entries(stripePrices)) {
+    if (!validPlans.has(planId)) continue;
+    if (intervals.monthly) map[intervals.monthly] = planId;
+    if (intervals.annual) map[intervals.annual] = planId;
+  }
+  return map;
+};
+const priceIdToPlan = buildPriceIdToPlanMap();
+
 /**
  * @description Resolve the plan name from a Stripe subscription object.
- * In webhook payloads, price.product is typically a string ID (not expanded),
- * so we check price.metadata first, then fall back to plan.metadata.
+ * Strategy (most-specific first):
+ *   1. config price-ID map (price_xxx → planId) — robust, no metadata dependency.
+ *   2. price.metadata.planId legacy fallback (works only if metadata was explicitly set).
+ *   3. plan.metadata.planId further legacy fallback.
+ *   4. 'free' when nothing resolves.
  * @param {Object} subscription - Stripe subscription object
  * @returns {string} plan name
  */
 const resolvePlan = (subscription) => {
   const item = subscription.items?.data?.[0];
-  const raw = item?.price?.metadata?.planId || item?.plan?.metadata?.planId;
-  return validatePlan(raw) || 'free';
+  const priceId = item?.price?.id;
+  if (priceId && priceIdToPlan[priceId]) {
+    return priceIdToPlan[priceId];
+  }
+  // Legacy fallback: price metadata set explicitly (e.g. test fixtures or manual Stripe edits)
+  const rawMeta = item?.price?.metadata?.planId || item?.plan?.metadata?.planId;
+  return validatePlan(rawMeta) || 'free';
 };
 
 /**
@@ -386,6 +414,18 @@ const handleSubscriptionUpdated = async (subscription, event) => {
     status: subscription.status,
   };
   if (newPeriodStart) fields.currentPeriodStart = newPeriodStart;
+  // Pending cancellation — record cancel_at_period_end flag and cancel_at date
+  // so the UI can show the user when their plan actually ends instead of treating
+  // it as an immediate downgrade. Does NOT change `plan` — subscription stays on
+  // the current plan until cancel_at.
+  if (typeof subscription.cancel_at_period_end === 'boolean') {
+    fields.cancelAtPeriodEnd = subscription.cancel_at_period_end;
+  }
+  if (subscription.cancel_at) {
+    fields.cancelAt = new Date(subscription.cancel_at * 1000);
+  } else if (subscription.cancel_at === null) {
+    fields.cancelAt = null;
+  }
 
   const updated = await SubscriptionRepository.updateIfEventNewer(String(existing._id), event.created, event.id, fields, 'subscription');
   if (!updated) {
@@ -423,7 +463,9 @@ const handleSubscriptionUpdated = async (subscription, event) => {
   const previousItems = event?.data?.previous_attributes?.items?.data;
   let planChangeResetTriggered = false;
   if (previousItems) {
-    const previousPlan = previousItems[0]?.price?.metadata?.planId
+    const previousPriceId = previousItems[0]?.price?.id;
+    const previousPlan = (previousPriceId && priceIdToPlan[previousPriceId])
+      || previousItems[0]?.price?.metadata?.planId
       || previousItems[0]?.plan?.metadata?.planId
       || null;
     if (previousPlan && previousPlan !== newPlan) {