fix(notifications): P2 extreme-audit P1 fixes before deploy

Independent audit verdict was NOT SAFE; all findings fixed:
- dispatcher Idempotency-Key is now per-attempt (${id}:${attempts}),
  not row id alone, so a transient-failure response cached by Resend
  cannot permanently suppress every retry and silently lose an email.
- enqueueDues is fully try/catch wrapped so a notifications-table or
  render failure can never throw into / wedge the Stripe money path.
- dues_lapsed dedupe falls back to the subscription id when periodEnd
  is null (canceled/deleted subs), so future lapses no longer collapse
  to one key and get suppressed. New test; suite 499.
- documented the dispatcher's once/min concurrency assumption.

app/api/cron/notifications/route.ts

@@ -4,10 +4,14 @@
 // (cron has none) so proxy.ts whitelists /api/cron; trust is the CRON_SECRET
 // shared-secret header, compared in constant time.
 //
-// Re-entrancy: a row is updated immediately after its own send, and sendEmail
-// passes the row id as Resend's Idempotency-Key, so an overlapping run cannot
-// double-send. Transient failures (retryable) stay pending for the next
-// minute until the attempt budget is exhausted; permanent ones go to 'failed'.
+// Re-entrancy: there is no row-level claim/lock, so two overlapping runs can
+// scan the same pending rows. This is safe because (a) the crontab fires once
+// a minute and a run drains <=20 rows in ~5s, so overlap is rare, and (b)
+// sendEmail passes a per-attempt Idempotency-Key (`${id}:${attempts}`):
+// concurrent runs of the SAME attempt dedupe at Resend, while the next
+// minute's retry of a transiently-failed row is a deliberately fresh send.
+// Transient failures stay pending until the attempt budget is exhausted;
+// permanent ones go to 'failed'.
 import { NextRequest, NextResponse } from 'next/server'
 import { timingSafeEqual } from 'node:crypto'
 import { createAdminClient } from '@/lib/supabase/admin'
@@ -63,7 +67,13 @@ export async function POST(req: NextRequest) {
       subject: row.subject as string,
       html: row.body_html as string,
       text: row.body_text as string,
-      idempotencyKey: row.id as string,
+      // Per-attempt, NOT row.id alone: Resend dedupes 24h on key+payload and
+      // its docs do not guarantee a failed response is excluded from that
+      // cache. A stable key would let a cached transient failure permanently
+      // suppress every later retry (email silently lost). Tying the key to
+      // the attempt number means concurrent runs of the SAME attempt still
+      // dedupe, but the next minute's real retry is a fresh send.
+      idempotencyKey: `${row.id}:${(row.attempts as number) ?? 0}`,
     })
 
     if (res.ok) {

app/api/stripe/webhook/[space]/route.ts

@@ -88,6 +88,11 @@ export async function POST(
   // inline (keeps this money path fast + retry-safe); the dispatcher cron
   // sends. ignoreDuplicates + the (space_id, dedupe_key) unique index make a
   // Stripe event replay (new event id, same invoice/period) a no-op.
+  //
+  // BEST-EFFORT: the entire body is wrapped so a notifications-table or
+  // render failure can NEVER throw into the money path. The Stripe ledger /
+  // member_billing / status writes must finalize even if email infra is
+  // down; a missed enqueue is acceptable, a wedged money path is not.
   async function enqueueDues(
     type: DuesNotificationType,
     args: {
@@ -97,45 +102,55 @@ export async function POST(
       currency?: string | null
       periodEnd?: string | null
       invoiceId?: string | null
+      subscriptionId?: string | null
     },
   ): Promise<void> {
-    if (!args.memberId) return
-    const { data: mem } = await admin
-      .from('space_members')
-      .select('email, display_name')
-      .eq('id', args.memberId)
-      .eq('space_id', spaceId)
-      .maybeSingle()
-    const recipient = ((mem?.email as string | null) || args.fallbackEmail || '').trim()
-    if (!recipient) return
-    const { subject, html, text } = renderDuesEmail({
-      type,
-      spaceName: await getSpaceName(),
-      memberName: (mem?.display_name as string | null) ?? null,
-      amount: args.amount ?? null,
-      currency: args.currency ?? null,
-      periodEnd: args.periodEnd ?? null,
-      manageUrl,
-    })
-    await admin.from('notifications').upsert(
-      {
-        space_id: spaceId,
-        member_id: args.memberId,
+    try {
+      if (!args.memberId) return
+      const { data: mem } = await admin
+        .from('space_members')
+        .select('email, display_name')
+        .eq('id', args.memberId)
+        .eq('space_id', spaceId)
+        .maybeSingle()
+      const recipient = ((mem?.email as string | null) || args.fallbackEmail || '').trim()
+      if (!recipient) return
+      const { subject, html, text } = renderDuesEmail({
         type,
-        channel: 'email',
-        recipient,
-        subject,
-        body_html: html,
-        body_text: text,
-        status: 'pending',
-        dedupe_key: duesDedupeKey(type, {
-          invoiceId: args.invoiceId,
-          memberId: args.memberId,
-          periodEnd: args.periodEnd,
-        }),
-      },
-      { onConflict: 'space_id,dedupe_key', ignoreDuplicates: true },
-    )
+        spaceName: await getSpaceName(),
+        memberName: (mem?.display_name as string | null) ?? null,
+        amount: args.amount ?? null,
+        currency: args.currency ?? null,
+        periodEnd: args.periodEnd ?? null,
+        manageUrl,
+      })
+      const { error: enqErr } = await admin.from('notifications').upsert(
+        {
+          space_id: spaceId,
+          member_id: args.memberId,
+          type,
+          channel: 'email',
+          recipient,
+          subject,
+          body_html: html,
+          body_text: text,
+          status: 'pending',
+          dedupe_key: duesDedupeKey(type, {
+            invoiceId: args.invoiceId,
+            memberId: args.memberId,
+            periodEnd: args.periodEnd,
+            subscriptionId: args.subscriptionId,
+          }),
+        },
+        { onConflict: 'space_id,dedupe_key', ignoreDuplicates: true },
+      )
+      if (enqErr) console.error(`[stripe webhook] enqueue ${type} failed:`, enqErr.message)
+    } catch (e) {
+      console.error(
+        `[stripe webhook] enqueue ${type} threw:`,
+        e instanceof Error ? e.message : e,
+      )
+    }
   }
 
   // Resolve our member: prefer metadata (set on the subscription + session),
@@ -211,7 +226,7 @@ export async function POST(
     // Dues lapsed past grace -> one "marked late" email per lapsed period
     // (dedupe is member + periodEnd, so next cycle can lapse again).
     if (desired === 'late') {
-      await enqueueDues('dues_lapsed', { memberId, periodEnd })
+      await enqueueDues('dues_lapsed', { memberId, periodEnd, subscriptionId: sub.id })
     }
   }