diff --git a/packages/db/prisma/migrations/20261009110000_billing_checkout_sessions/migration.sql b/packages/db/prisma/migrations/20261009110000_billing_checkout_sessions/migration.sql
new file mode 100644
index 00000000..30dd512a
--- /dev/null
+++ b/packages/db/prisma/migrations/20261009110000_billing_checkout_sessions/migration.sql
@@ -0,0 +1,21 @@
+-- Preserve every checkout reference_id so superseded Xendit sessions still resolve on webhook.
+CREATE TABLE "billing_checkout_sessions" (
+    "provider_reference" TEXT NOT NULL,
+    "user_id" TEXT NOT NULL,
+    "workspace_id" TEXT NOT NULL,
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    CONSTRAINT "billing_checkout_sessions_pkey" PRIMARY KEY ("provider_reference")
+);
+
+CREATE INDEX "billing_checkout_sessions_workspace_id_created_at_idx"
+  ON "billing_checkout_sessions"("workspace_id", "created_at");
+
+ALTER TABLE "billing_checkout_sessions" ADD CONSTRAINT "billing_checkout_sessions_user_id_fkey"
+  FOREIGN KEY ("user_id") REFERENCES "user"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+ALTER TABLE "billing_checkout_sessions" ADD CONSTRAINT "billing_checkout_sessions_workspace_id_fkey"
+  FOREIGN KEY ("workspace_id") REFERENCES "organization"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+INSERT INTO "billing_checkout_sessions" ("provider_reference", "user_id", "workspace_id", "created_at")
+SELECT "provider_reference", "user_id", "workspace_id", COALESCE("created_at", CURRENT_TIMESTAMP)
+FROM "subscriptions"
+WHERE "provider_reference" IS NOT NULL;
diff --git a/packages/db/prisma/schema.prisma b/packages/db/prisma/schema.prisma
index dbdf5ea7..cd040955 100644
--- a/packages/db/prisma/schema.prisma
+++ b/packages/db/prisma/schema.prisma
@@ -29,6 +29,7 @@ model User {
   actionAutoReviewPreferences ActionAutoReviewPreference[]
   devices          Device[]
   subscriptions    Subscription[]
+  billingCheckoutSessions BillingCheckoutSession[]
   paymentEvents    PaymentEvent[]
   usageReservations UsageReservation[]
   usageLedger       UsageLedger[]
@@ -125,6 +126,7 @@ model Organization {
   runtimes    Runtime[]
   keyEnvelopes KeyEnvelope[]
   subscriptions Subscription[]
+  billingCheckoutSessions BillingCheckoutSession[]
   paymentEvents  PaymentEvent[]
   usageReservations UsageReservation[]
   usageLedger       UsageLedger[]
@@ -202,6 +204,19 @@ model Subscription {
   @@map("subscriptions")
 }
 
+/// Immutable lookup from Xendit reference_id to workspace for every checkout started.
+model BillingCheckoutSession {
+  providerReference String       @id @map("provider_reference")
+  userId            String       @map("user_id")
+  user              User         @relation(fields: [userId], references: [id], onDelete: Cascade)
+  workspaceId       String       @map("workspace_id")
+  workspace         Organization @relation(fields: [workspaceId], references: [id], onDelete: Cascade)
+  createdAt         DateTime     @default(now()) @map("created_at")
+
+  @@index([workspaceId, createdAt])
+  @@map("billing_checkout_sessions")
+}
+
 model PaymentEvent {
   id              String       @id @default(cuid())
   userId          String       @map("user_id")
diff --git a/packages/db/src/platform.test.ts b/packages/db/src/platform.test.ts
index 986253bf..1a48b7a1 100644
--- a/packages/db/src/platform.test.ts
+++ b/packages/db/src/platform.test.ts
@@ -473,4 +473,54 @@ describe("platform control-plane repositories", () => {
       data: { status: "released", finalizedAt: new Date("2026-09-02T00:00:00.000Z") },
     });
   });
+
+  it("resolves payment targets for superseded checkout references", async () => {
+    const { findPaymentTargetByProviderReference } = await import("./platform.js");
+    const findUniqueSession = vi.fn().mockResolvedValue({
+      userId: "user-1",
+      workspaceId: "workspace-1",
+    });
+    const subscriptionFindUnique = vi.fn();
+    const db = {
+      billingCheckoutSession: { findUnique: findUniqueSession },
+      subscription: { findUnique: subscriptionFindUnique },
+    };
+
+    await expect(findPaymentTargetByProviderReference(db as any, "checkout-old")).resolves.toEqual({
+      userId: "user-1",
+      workspaceId: "workspace-1",
+    });
+    expect(subscriptionFindUnique).not.toHaveBeenCalled();
+  });
+
+  it("records every checkout reference when a workspace starts a new session", async () => {
+    const { beginCheckout } = await import("./platform.js");
+    const createSession = vi.fn().mockResolvedValue(undefined);
+    const upsert = vi.fn().mockResolvedValue(undefined);
+    const db = {
+      $transaction: async (steps: unknown[]) => {
+        for (const step of steps) {
+          if (typeof step === "object" && step !== null && "then" in step) await step;
+        }
+      },
+      billingCheckoutSession: { create: createSession },
+      subscription: { upsert },
+    };
+
+    await beginCheckout(db as any, {
+      userId: "user-1",
+      workspaceId: "workspace-1",
+      provider: "xendit",
+      providerReference: "checkout-2",
+    });
+
+    expect(createSession).toHaveBeenCalledWith({
+      data: {
+        providerReference: "checkout-2",
+        userId: "user-1",
+        workspaceId: "workspace-1",
+      },
+    });
+    expect(upsert).toHaveBeenCalledOnce();
+  });
 });
diff --git a/packages/db/src/platform.ts b/packages/db/src/platform.ts
index 8466f11e..0439e653 100644
--- a/packages/db/src/platform.ts
+++ b/packages/db/src/platform.ts
@@ -524,6 +524,11 @@ export async function tombstoneEncryptedSyncObject(
 }
 
 export async function findPaymentTargetByProviderReference(db: Db, providerReference: string) {
+  const session = await db.billingCheckoutSession.findUnique({
+    where: { providerReference },
+    select: { userId: true, workspaceId: true },
+  });
+  if (session) return session;
   return db.subscription.findUnique({
     where: { providerReference },
     select: { userId: true, workspaceId: true },
@@ -534,24 +539,33 @@ export async function beginCheckout(
   db: Db,
   input: { userId: string; workspaceId: string; provider: string; providerReference: string },
 ): Promise<void> {
-  await db.subscription.upsert({
-    where: { workspaceId: input.workspaceId },
-    create: {
-      userId: input.userId,
-      workspaceId: input.workspaceId,
-      planCode: "plus",
-      state: "checkout_pending",
-      provider: input.provider,
-      providerReference: input.providerReference,
-    },
-    update: {
-      planCode: "plus",
-      state: "checkout_pending",
-      provider: input.provider,
-      providerReference: input.providerReference,
-      graceEndsAt: null,
-    },
-  });
+  await db.$transaction([
+    db.billingCheckoutSession.create({
+      data: {
+        providerReference: input.providerReference,
+        userId: input.userId,
+        workspaceId: input.workspaceId,
+      },
+    }),
+    db.subscription.upsert({
+      where: { workspaceId: input.workspaceId },
+      create: {
+        userId: input.userId,
+        workspaceId: input.workspaceId,
+        planCode: "plus",
+        state: "checkout_pending",
+        provider: input.provider,
+        providerReference: input.providerReference,
+      },
+      update: {
+        planCode: "plus",
+        state: "checkout_pending",
+        provider: input.provider,
+        providerReference: input.providerReference,
+        graceEndsAt: null,
+      },
+    }),
+  ]);
 }
 
 interface PlatformTransaction {