fix: scope display contact lookup to workspace (ENG-818)

The doesContactExist helper used by POST /api/v2/client/{workspaceId}/displays
checked contact existence by id only, allowing a caller to bind a display
in one workspace to a contact from a different workspace.

PR #7984 previously fixed this by adding an environmentId filter, but the
Formbricks 5 migration (PR #8017) dropped that filter when renaming
environmentId → workspaceId. Re-apply the workspace check.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/app/api/v2/client/[workspaceId]/displays/lib/contact.test.ts

@@ -21,24 +21,25 @@ vi.mock("react", async () => {
 });
 
 const contactId = "test-contact-id";
+const workspaceId = "test-workspace-id";
 
 describe("doesContactExist", () => {
   afterEach(() => {
     vi.resetAllMocks();
   });
 
-  test("should return true if contact exists", async () => {
+  test("should return true if contact exists in the workspace", async () => {
     vi.mocked(prisma.contact.findFirst).mockResolvedValue({
       id: contactId,
       createdAt: new Date(),
       updatedAt: new Date(),
     } as any);
 
-    const result = await doesContactExist(contactId);
+    const result = await doesContactExist(contactId, workspaceId);
 
     expect(result).toBe(true);
     expect(prisma.contact.findFirst).toHaveBeenCalledWith({
-      where: { id: contactId },
+      where: { id: contactId, workspaceId },
       select: { id: true },
     });
   });
@@ -46,11 +47,11 @@ describe("doesContactExist", () => {
   test("should return false if contact does not exist in the workspace", async () => {
     vi.mocked(prisma.contact.findFirst).mockResolvedValue(null);
 
-    const result = await doesContactExist(contactId);
+    const result = await doesContactExist(contactId, workspaceId);
 
     expect(result).toBe(false);
     expect(prisma.contact.findFirst).toHaveBeenCalledWith({
-      where: { id: contactId },
+      where: { id: contactId, workspaceId },
       select: { id: true },
     });
   });

apps/web/app/api/v2/client/[workspaceId]/displays/lib/contact.ts

@@ -1,10 +1,11 @@
 import { cache as reactCache } from "react";
 import { prisma } from "@formbricks/database";
 
-export const doesContactExist = reactCache(async (id: string): Promise<boolean> => {
+export const doesContactExist = reactCache(async (id: string, workspaceId: string): Promise<boolean> => {
   const contact = await prisma.contact.findFirst({
     where: {
       id,
+      workspaceId,
     },
     select: {
       id: true,

apps/web/app/api/v2/client/[workspaceId]/displays/lib/display.test.ts

@@ -87,7 +87,7 @@ describe("createDisplay", () => {
     const result = await createDisplay(displayInput);
 
     expect(validateInputs).toHaveBeenCalledWith([displayInput, expect.any(Object)]);
-    expect(doesContactExist).toHaveBeenCalledWith(contactId);
+    expect(doesContactExist).toHaveBeenCalledWith(contactId, workspaceId);
     expect(prisma.display.create).toHaveBeenCalledWith({
       data: {
         survey: { connect: { id: surveyId } },
@@ -121,7 +121,7 @@ describe("createDisplay", () => {
     const result = await createDisplay(displayInput);
 
     expect(validateInputs).toHaveBeenCalledWith([displayInput, expect.any(Object)]);
-    expect(doesContactExist).toHaveBeenCalledWith(contactId);
+    expect(doesContactExist).toHaveBeenCalledWith(contactId, workspaceId);
     expect(prisma.display.create).toHaveBeenCalledWith({
       data: {
         survey: { connect: { id: surveyId } },
@@ -148,7 +148,7 @@ describe("createDisplay", () => {
     vi.mocked(prisma.survey.findUnique).mockResolvedValue(null);
 
     await expect(createDisplay(displayInput)).rejects.toThrow(new ResourceNotFoundError("Survey", surveyId));
-    expect(doesContactExist).toHaveBeenCalledWith(contactId);
+    expect(doesContactExist).toHaveBeenCalledWith(contactId, workspaceId);
     expect(prisma.survey.findUnique).toHaveBeenCalledWith({
       where: { id: surveyId, workspaceId },
     });

apps/web/app/api/v2/client/[workspaceId]/displays/lib/display.ts

@@ -14,7 +14,7 @@ export const createDisplay = async (displayInput: TDisplayCreateInputV2): Promis
   const { contactId, surveyId, workspaceId } = displayInput;
 
   try {
-    const contactExists = contactId ? await doesContactExist(contactId) : false;
+    const contactExists = contactId ? await doesContactExist(contactId, workspaceId) : false;
 
     const survey = await prisma.survey.findUnique({
       where: {