diff --git a/server/package.json b/server/package.json
index 5e2aa8c5b..400e203e4 100644
--- a/server/package.json
+++ b/server/package.json
@@ -21,7 +21,7 @@
 		"workers": "bun src/workers.ts",
 		"cron": "bun src/cron.ts",
 		"check": "bun src/check.ts",
-		"t": "ENV_FILE=.env infisical run --env=dev --recursive -- bun tests/testRunner/runParallelGroupsV3.ts",
+		"t": "cd ../ && bun t $* && cd ./server",
 		"parallel-tests": "ENV_FILE=.env infisical run --env=dev --recursive -- bun tests/testRunner/runParallelGroupsV3.ts",
 		"parallel-tests:v1": "ENV_FILE=.env infisical run --env=dev --recursive -- bun tests/testRunner/runParallelGroups.ts",
 		"parallel-tests:verbose": "ENV_FILE=.env infisical run --env=dev --recursive -- bun tests/testRunner/runParallelGroups.ts --verbose",
diff --git a/server/src/internal/customers/internalHandlers/handleGetInvoiceLineItems.ts b/server/src/internal/customers/internalHandlers/handleGetInvoiceLineItems.ts
index d7fc8833b..e4d9990b2 100644
--- a/server/src/internal/customers/internalHandlers/handleGetInvoiceLineItems.ts
+++ b/server/src/internal/customers/internalHandlers/handleGetInvoiceLineItems.ts
@@ -1,4 +1,4 @@
-import { Scopes, stripeToAtmnAmount } from "@autumn/shared";
+import { ProcessorType, Scopes, stripeToAtmnAmount } from "@autumn/shared";
 import { z } from "zod/v4";
 import { createStripeCli } from "@/external/connect/createStripeCli";
 import { createRoute } from "@/honoMiddlewares/routeHandler.js";
@@ -32,10 +32,15 @@ export const handleGetInvoiceLineItems = createRoute({
 				org: ctx.org,
 				env: ctx.env,
 			});
-			const autumnInvoices = await InvoiceService.getMany({
-				db,
-				ids: invoice_ids,
-			});
+			const autumnInvoices = (
+				await InvoiceService.getMany({
+					db,
+					ids: invoice_ids,
+				})
+			).filter(
+				(inv) =>
+					(inv.processor_type ?? ProcessorType.Stripe) === ProcessorType.Stripe,
+			);
 			const stripeInvoices = [];
 			for (const invoice of autumnInvoices) {
 				// Throttle to avoid Stripe rate limits.
diff --git a/server/src/internal/invoices/InvoiceService.ts b/server/src/internal/invoices/InvoiceService.ts
index 6b3aea1f7..50b29486f 100644
--- a/server/src/internal/invoices/InvoiceService.ts
+++ b/server/src/internal/invoices/InvoiceService.ts
@@ -9,6 +9,7 @@ import {
 	type InvoiceStatus,
 	invoices,
 	type Organization,
+	ProcessorType,
 	RecaseError,
 	stripeToAtmnAmount,
 } from "@autumn/shared";
@@ -33,6 +34,7 @@ export const processInvoice = ({
 		// product_ids: invoice.product_ids,
 		plan_ids: invoice.product_ids,
 		stripe_id: invoice.stripe_id,
+		processor_type: invoice.processor_type ?? ProcessorType.Stripe,
 		status: invoice.status ?? "",
 		total: invoice.total,
 		currency: invoice.currency,
@@ -227,6 +229,7 @@ export class InvoiceService {
 			product_ids: uniqueProductIds,
 			created_at: stripeInvoice.created * 1000,
 			stripe_id: stripeInvoice.id!,
+			processor_type: ProcessorType.Stripe,
 			hosted_invoice_url: stripeInvoice.hosted_invoice_url || null,
 			status: status || (stripeInvoice.status as InvoiceStatus | null),
 			internal_product_ids: uniqueInternalProductIds,
diff --git a/server/src/internal/invoices/handlers/handleRedirectToInvoice.ts b/server/src/internal/invoices/handlers/handleRedirectToInvoice.ts
index 96a73377b..b2177824b 100644
--- a/server/src/internal/invoices/handlers/handleRedirectToInvoice.ts
+++ b/server/src/internal/invoices/handlers/handleRedirectToInvoice.ts
@@ -1,4 +1,4 @@
-import { ErrCode, RecaseError, Scopes } from "@autumn/shared";
+import { ErrCode, ProcessorType, RecaseError, Scopes } from "@autumn/shared";
 import { StatusCodes } from "http-status-codes";
 import { createStripeCli } from "@/external/connect/createStripeCli.js";
 import { createRoute } from "@/honoMiddlewares/routeHandler.js";
@@ -28,6 +28,16 @@ export const handleRedirectToInvoice = createRoute({
 			});
 		}
 
+		if (
+			(invoice.processor_type ?? ProcessorType.Stripe) !== ProcessorType.Stripe
+		) {
+			throw new RecaseError({
+				message: "Hosted invoice URL is not available for this invoice",
+				code: ErrCode.InvalidRequest,
+				statusCode: StatusCodes.NOT_FOUND,
+			});
+		}
+
 		try {
 			const org = invoice.customer.org;
 			const env = invoice.customer.env;
diff --git a/server/src/internal/invoices/utils/initInvoiceFromStripe.ts b/server/src/internal/invoices/utils/initInvoiceFromStripe.ts
index 460120c84..f851f73c7 100644
--- a/server/src/internal/invoices/utils/initInvoiceFromStripe.ts
+++ b/server/src/internal/invoices/utils/initInvoiceFromStripe.ts
@@ -3,6 +3,7 @@ import {
 	type FullCustomer,
 	type FullProduct,
 	type InsertInvoice,
+	ProcessorType,
 	secondsToMs,
 	stripeToAtmnAmount,
 } from "@autumn/shared";
@@ -62,6 +63,7 @@ export const initInvoiceFromStripe = async ({
 		internal_product_ids: [...new Set(internalProductIds)],
 		created_at: secondsToMs(stripeInvoice.created),
 		stripe_id: stripeInvoice.id!,
+		processor_type: ProcessorType.Stripe,
 		hosted_invoice_url: stripeInvoice.hosted_invoice_url || null,
 		status: stripeInvoice.status as string | undefined,
 		internal_entity_id: internalEntityId || null,
diff --git a/server/tests/integration/db/full-subject/utils/fullSubjectScenarioBuilders.ts b/server/tests/integration/db/full-subject/utils/fullSubjectScenarioBuilders.ts
index bd53751bd..0d4cba635 100644
--- a/server/tests/integration/db/full-subject/utils/fullSubjectScenarioBuilders.ts
+++ b/server/tests/integration/db/full-subject/utils/fullSubjectScenarioBuilders.ts
@@ -19,6 +19,7 @@ import {
 	FeatureType,
 	type InvoiceRow,
 	InvoiceStatus,
+	ProcessorType,
 	type SubscriptionRow,
 } from "@autumn/shared";
 import { AllowanceType } from "@shared/models/productModels/entModels/entModels.js";
@@ -401,6 +402,7 @@ const buildInvoice = ({
 	internal_customer_id: customer.internal_id,
 	internal_entity_id: internalEntityId,
 	stripe_id: `stripe_inv_${key}_${suffix}`,
+	processor_type: ProcessorType.Stripe,
 	status: InvoiceStatus.Paid,
 	hosted_invoice_url: null,
 	total: 1000,
diff --git a/server/tests/unit/full-subject-cache/sanitizeCachedPayloads.test.ts b/server/tests/unit/full-subject-cache/sanitizeCachedPayloads.test.ts
index eeccf028a..b8b97b431 100644
--- a/server/tests/unit/full-subject-cache/sanitizeCachedPayloads.test.ts
+++ b/server/tests/unit/full-subject-cache/sanitizeCachedPayloads.test.ts
@@ -2,6 +2,7 @@ import { describe, expect, test } from "bun:test";
 import {
 	type AggregatedFeatureBalanceSchema,
 	AppEnv,
+	ProcessorType,
 	ProductSchema,
 	type SubjectBalance,
 } from "@autumn/shared";
@@ -142,6 +143,66 @@ describe("normalizeFromSchema (core walker)", () => {
 			normalizeFromSchema({ schema, data: "not an object" }),
 		).not.toThrow();
 	});
+
+	// processor_type cache safety: confirms `.default()` fires symmetrically
+	// through both walkers. This is the core guarantee Option A relies on —
+	// Upstash cjson strips the field for old cached entries and the walker
+	// must hydrate it back to ProcessorType.Stripe so consumers see a defined
+	// value. The explicit-null case is documented as walker passthrough; the
+	// `?? ProcessorType.Stripe` consumer mask is what handles that.
+
+	test("ZodDefault fires for ProcessorType enum on undefined (FullSubject walker)", () => {
+		const schema = z.object({
+			processor_type: z.enum(ProcessorType).default(ProcessorType.Stripe),
+		});
+		const result = normalizeFromSchema<{ processor_type: ProcessorType }>({
+			schema,
+			data: {},
+		});
+		expect(result.processor_type).toBe(ProcessorType.Stripe);
+	});
+
+	test("ZodDefault passes through explicit null (FullSubject walker)", () => {
+		const schema = z.object({
+			processor_type: z.enum(ProcessorType).default(ProcessorType.Stripe),
+		});
+		const result = normalizeFromSchema<{
+			processor_type: ProcessorType | null;
+		}>({
+			schema,
+			data: { processor_type: null },
+		});
+		// Documents Option A's known limitation: `.default()` only fires for
+		// undefined. The consumer-side `?? ProcessorType.Stripe` (in
+		// processInvoice / latent breakage filters) covers this case.
+		expect(result.processor_type).toBeNull();
+	});
+
+	test("ZodDefault does NOT fire on primitive leaves in cacheUtils walker (documented limitation)", () => {
+		// The FullCustomer / cacheUtils walker has no leaf-level ZodDefault
+		// application — for primitive types like ZodEnum, it returns `data`
+		// unchanged (see normalizeFromSchema.ts:139). This is a known
+		// asymmetry vs the FullSubject walker (which DOES handle ZodDefault
+		// at primitive leaves). Out of scope to fix in this stage; tracked as
+		// follow-up in the invoice-schema-rename-plan.
+		//
+		// Why this is OK for processor_type: the consumer-side
+		// `?? ProcessorType.Stripe` mask in `processInvoice` and the latent
+		// breakage filters covers the undefined case from this walker just
+		// as it covers the null case from the FullSubject walker. The wire
+		// always emits a defined value.
+		const schema = z.object({
+			processor_type: z.enum(ProcessorType).default(ProcessorType.Stripe),
+		});
+		const result = normalizeFromSchemaCacheUtils<{
+			processor_type: ProcessorType | undefined;
+		}>({
+			schema: schema as unknown as z.ZodTypeAny,
+			data: {},
+		});
+		// Walker returns the field undefined. Consumer `??` is what masks it.
+		expect(result.processor_type).toBeUndefined();
+	});
 });
 
 describe("sanitizeCachedSubjectBalance", () => {
@@ -454,6 +515,141 @@ describe("sanitizeCachedFullSubject", () => {
 	});
 });
 
+// ═══════════════════════════════════════════════════════════════════════════════
+// processor_type — multi-processor invoice scaffolding
+//
+// Locks in the Option A contract: the schema's `.default(ProcessorType.Stripe)`
+// fires through the walker for `undefined` (covers cjson-stripped fields on
+// pre-deploy cached entries), `null` is passed through unchanged (consumers
+// mask via `?? ProcessorType.Stripe`), and explicit `"stripe"` / `"revenuecat"`
+// values round-trip cleanly without over-correction.
+// ═══════════════════════════════════════════════════════════════════════════════
+
+describe("sanitizeCachedFullSubject — processor_type (Option A walker behavior)", () => {
+	const buildCachedFullSubject = (): unknown => ({
+		subjectType: "customer",
+		customerId: "cus_proc",
+		internalCustomerId: "cus_int_proc",
+		_cachedAt: Date.now(),
+		subjectViewEpoch: 1,
+		meteredFeatures: [],
+		customerEntitlementIdsByFeatureId: {},
+		customer: {
+			internal_id: "cus_int_proc",
+			org_id: "org_proc",
+			env: AppEnv.Live,
+			created_at: 1,
+		},
+		customer_products: [],
+		products: [],
+		entitlements: [],
+		prices: [],
+		free_trials: [],
+		subscriptions: [],
+		invoices: [],
+		flags: {},
+	});
+
+	const buildInvoice = (
+		overrides: Record<string, unknown> = {},
+	): Record<string, unknown> => ({
+		id: "inv_proc",
+		created_at: 1,
+		internal_customer_id: "cus_int_proc",
+		product_ids: [],
+		internal_product_ids: [],
+		stripe_id: "in_proc",
+		total: 100,
+		currency: "usd",
+		discounts: [],
+		items: [],
+		...overrides,
+	});
+
+	test("walker fills missing processor_type via ZodDefault → stripe", () => {
+		// Pre-deploy cache entries don't have the field at all (cjson stripped
+		// or never written).
+		const malformed = buildCachedFullSubject() as unknown as Record<
+			string,
+			unknown
+		>;
+		malformed.invoices = [buildInvoice()]; // no processor_type key
+		const result = sanitizeCachedFullSubject({
+			cachedFullSubject: malformed as unknown as CachedFullSubject,
+		});
+		expect(result.invoices[0].processor_type).toBe(ProcessorType.Stripe);
+	});
+
+	test("walker passes through explicit null processor_type unchanged", () => {
+		// Documents the Option A limitation: `.default()` only fires for
+		// undefined. Consumers (processInvoice, latent breakage filters)
+		// handle the null case via `?? ProcessorType.Stripe`. This test
+		// guards against any future "convenience" change that silently
+		// coerces null at the walker level — consumer code relies on the
+		// passthrough semantics.
+		const malformed = buildCachedFullSubject() as unknown as Record<
+			string,
+			unknown
+		>;
+		malformed.invoices = [buildInvoice({ processor_type: null })];
+		const result = sanitizeCachedFullSubject({
+			cachedFullSubject: malformed as unknown as CachedFullSubject,
+		});
+		expect(result.invoices[0].processor_type).toBeNull();
+	});
+
+	test("walker preserves explicit processor_type='stripe'", () => {
+		const malformed = buildCachedFullSubject() as unknown as Record<
+			string,
+			unknown
+		>;
+		malformed.invoices = [
+			buildInvoice({ processor_type: ProcessorType.Stripe }),
+		];
+		const result = sanitizeCachedFullSubject({
+			cachedFullSubject: malformed as unknown as CachedFullSubject,
+		});
+		expect(result.invoices[0].processor_type).toBe(ProcessorType.Stripe);
+	});
+
+	test("walker preserves explicit processor_type='revenuecat' (no over-correction)", () => {
+		const malformed = buildCachedFullSubject() as unknown as Record<
+			string,
+			unknown
+		>;
+		malformed.invoices = [
+			buildInvoice({ processor_type: ProcessorType.RevenueCat }),
+		];
+		const result = sanitizeCachedFullSubject({
+			cachedFullSubject: malformed as unknown as CachedFullSubject,
+		});
+		expect(result.invoices[0].processor_type).toBe(ProcessorType.RevenueCat);
+	});
+
+	test("end-to-end: walker null + processInvoice consumer → wire stripe", async () => {
+		// Composite contract: walker leaves null, consumer masks. Documents the
+		// agreed Option A pattern as runnable code so a future regression in
+		// either the walker OR the consumer trips this test.
+		const malformed = buildCachedFullSubject() as unknown as Record<
+			string,
+			unknown
+		>;
+		malformed.invoices = [buildInvoice({ processor_type: null })];
+		const sanitized = sanitizeCachedFullSubject({
+			cachedFullSubject: malformed as unknown as CachedFullSubject,
+		});
+		expect(sanitized.invoices[0].processor_type).toBeNull();
+
+		const { processInvoice } = await import(
+			"@/internal/invoices/InvoiceService.js"
+		);
+		const wire = processInvoice({
+			invoice: sanitized.invoices[0],
+		});
+		expect(wire.processor_type).toBe(ProcessorType.Stripe);
+	});
+});
+
 describe("sanitizeCachedAggregatedFeatureBalance", () => {
 	test("fills undefined at nullable positions for AggregatedFeatureBalance", () => {
 		// AggregatedFeatureBalance entities is .nullish() — undefined should
diff --git a/server/tests/unit/invoices/processInvoice.test.ts b/server/tests/unit/invoices/processInvoice.test.ts
new file mode 100644
index 000000000..50aa23f20
--- /dev/null
+++ b/server/tests/unit/invoices/processInvoice.test.ts
@@ -0,0 +1,86 @@
+import { describe, expect, test } from "bun:test";
+import { type Invoice, ProcessorType } from "@autumn/shared";
+import { processInvoice } from "@/internal/invoices/InvoiceService.js";
+
+// ═══════════════════════════════════════════════════════════════════════════════
+// processInvoice — processor_type wire mapping
+//
+// `processInvoice` is the single boundary between the raw Drizzle/cached
+// `Invoice` row and the public V5 `ApiInvoiceV1` wire shape. It must always
+// emit a defined `processor_type` regardless of input shape.
+//
+// Coverage matrix:
+//   • explicit "stripe"     → wire "stripe"
+//   • explicit "revenuecat" → wire "revenuecat"
+//   • null                  → wire "stripe" (consumer `??` mask, since
+//                              ZodDefault doesn't fire on explicit null)
+//   • undefined             → wire "stripe" (same `??` mask covers it; the
+//                              schema's ZodDefault would also fire through
+//                              the cache walker before reaching this point)
+//
+// Together these tests prove the wire never emits null/undefined for the new
+// optional field, regardless of where the input row came from (DB, cache,
+// pre-deploy cached entry).
+// ═══════════════════════════════════════════════════════════════════════════════
+
+const buildBaseInvoice = (overrides: Partial<Invoice> = {}): Invoice =>
+	({
+		id: "inv_test",
+		created_at: 1_700_000_000_000,
+		product_ids: [],
+		internal_product_ids: [],
+		internal_customer_id: "cus_int_test",
+		internal_entity_id: null,
+		stripe_id: "in_test",
+		status: "paid",
+		hosted_invoice_url: null,
+		total: 100,
+		amount_paid: 100,
+		refunded_amount: 0,
+		currency: "usd",
+		discounts: [],
+		items: [],
+		processor_type: ProcessorType.Stripe,
+		...overrides,
+	}) as Invoice;
+
+describe("processInvoice — processor_type wire mapping", () => {
+	test("explicit stripe → wire stripe", () => {
+		const wire = processInvoice({
+			invoice: buildBaseInvoice({ processor_type: ProcessorType.Stripe }),
+		});
+		expect(wire.processor_type).toBe(ProcessorType.Stripe);
+		expect(wire.stripe_id).toBe("in_test");
+	});
+
+	test("explicit revenuecat → wire revenuecat", () => {
+		const wire = processInvoice({
+			invoice: buildBaseInvoice({
+				processor_type: ProcessorType.RevenueCat,
+				stripe_id: "rc:txn_test",
+			}),
+		});
+		expect(wire.processor_type).toBe(ProcessorType.RevenueCat);
+		expect(wire.stripe_id).toBe("rc:txn_test");
+	});
+
+	test("null processor_type masks to stripe via consumer `??`", () => {
+		// Simulates a cached payload from a DB row with NULL processor_type
+		// that survived the cjson roundtrip without being stripped.
+		const wire = processInvoice({
+			invoice: buildBaseInvoice({
+				processor_type: null as unknown as ProcessorType,
+			}),
+		});
+		expect(wire.processor_type).toBe(ProcessorType.Stripe);
+	});
+
+	test("undefined processor_type masks to stripe via consumer `??`", () => {
+		// Simulates a raw row from the cache walker that had the field
+		// stripped by Upstash cjson (the most common pre-deploy case).
+		const raw = buildBaseInvoice();
+		delete (raw as Record<string, unknown>).processor_type;
+		const wire = processInvoice({ invoice: raw });
+		expect(wire.processor_type).toBe(ProcessorType.Stripe);
+	});
+});
diff --git a/shared/api/others/apiInvoice/apiInvoiceV1.ts b/shared/api/others/apiInvoice/apiInvoiceV1.ts
index 0741fde29..4fa5d96fb 100644
--- a/shared/api/others/apiInvoice/apiInvoiceV1.ts
+++ b/shared/api/others/apiInvoice/apiInvoiceV1.ts
@@ -1,4 +1,5 @@
 import { z } from "zod/v4";
+import { ProcessorType } from "../../../models/genModels/genEnums";
 
 export const ApiInvoiceV1Schema = z.object({
 	plan_ids: z.array(z.string()).meta({
@@ -9,6 +10,13 @@ export const ApiInvoiceV1Schema = z.object({
 		description: "The Stripe invoice ID",
 		example: "in_1A2B3C4D5E6F7G8H",
 	}),
+	processor_type: z
+		.enum(ProcessorType)
+		.default(ProcessorType.Stripe)
+		.meta({
+			description: "The billing processor that owns this invoice.",
+			example: "stripe",
+		}),
 	status: z.string().meta({
 		description: "The status of the invoice",
 		example: "paid",
diff --git a/shared/models/cusModels/invoiceModels/invoiceModels.ts b/shared/models/cusModels/invoiceModels/invoiceModels.ts
index 056c46d61..c15a57825 100644
--- a/shared/models/cusModels/invoiceModels/invoiceModels.ts
+++ b/shared/models/cusModels/invoiceModels/invoiceModels.ts
@@ -1,4 +1,5 @@
 import { z } from "zod/v4";
+import { ProcessorType } from "../../genModels/genEnums.js";
 
 export enum InvoiceStatus {
 	Draft = "draft",
@@ -34,6 +35,7 @@ export const InvoiceSchema = z.object({
 
 	// Stripe fields
 	stripe_id: z.string(),
+	processor_type: z.enum(ProcessorType).default(ProcessorType.Stripe),
 	status: z.nativeEnum(InvoiceStatus).nullable().optional(),
 	hosted_invoice_url: z.string().nullable(),
 
diff --git a/shared/models/cusModels/invoiceModels/invoiceTable.ts b/shared/models/cusModels/invoiceModels/invoiceTable.ts
index 157344cc5..f719fdbcd 100644
--- a/shared/models/cusModels/invoiceModels/invoiceTable.ts
+++ b/shared/models/cusModels/invoiceModels/invoiceTable.ts
@@ -25,6 +25,7 @@ export const invoices = pgTable(
 		internal_entity_id: text("internal_entity_id"),
 
 		stripe_id: text("stripe_id").notNull(),
+		processor_type: text("processor_type"),
 		status: text("status").notNull().default("draft"),
 		hosted_invoice_url: text("hosted_invoice_url"),
 		total: numeric({ mode: "number" }).notNull().default(0),