fix(launch-flow): auto-link /join signups to existing PreRegistration

When a /join submitter's email matches a pending/selected/invited
PreRegistration, mark the pre-reg as accepted and link memberId to the
new Member. Prevents the same person from appearing as both an active
member and an unaccepted pre-registrant. Silent — no email, no UI.

Adds the PreRegistration mock to helcim-customer and free-signup-flow
test suites, since both invoke the customer handler at runtime.

server/api/helcim/customer.post.js

@@ -2,6 +2,7 @@ import { getRequestHeader, getRequestIP } from 'h3'
 import Member from '../../models/member.js'
 import { connectDB } from '../../utils/mongoose.js'
 import { createHelcimCustomer } from '../../utils/helcim.js'
+import PreRegistration from '../../models/preRegistration.js'
 import { sendMagicLink } from '../../utils/magicLink.js'
 import { setPaymentBridgeCookie } from '../../utils/auth.js'
 import { rateLimit } from '../../utils/rateLimit.js'
@@ -82,6 +83,32 @@ export default defineEventHandler(async (event) => {
       })
     }
 
+    // If this email matches a pending pre-registrant, mark the PreRegistration
+    // as accepted and link it to the new Member. Silent — keeps /join and
+    // /admin/pre-registrants from showing the same person twice.
+    try {
+      const preReg = await PreRegistration.findOne({ email: normalizedEmail })
+      if (
+        preReg &&
+        !preReg.memberId &&
+        ['pending', 'selected', 'invited'].includes(preReg.status)
+      ) {
+        await PreRegistration.findByIdAndUpdate(
+          preReg._id,
+          {
+            $set: {
+              status: 'accepted',
+              acceptedAt: new Date(),
+              memberId: member._id,
+            },
+          },
+          { runValidators: false }
+        )
+      }
+    } catch (linkError) {
+      console.error('Failed to link PreRegistration to new member:', linkError)
+    }
+
     await sendMagicLink(normalizedEmail, {
       subject: 'Verify your Ghost Guild signup',
       intro: 'Verify your email to finish your Ghost Guild signup:',

tests/server/api/free-signup-flow.test.js

@@ -20,6 +20,9 @@ vi.mock('../../../server/models/member.js', () => ({
     findOneAndUpdate: vi.fn()
   }
 }))
+vi.mock('../../../server/models/preRegistration.js', () => ({
+  default: { findOne: vi.fn().mockResolvedValue(null), findByIdAndUpdate: vi.fn() }
+}))
 vi.mock('../../../server/utils/mongoose.js', () => ({ connectDB: vi.fn() }))
 vi.mock('../../../server/utils/helcim.js', () => ({
   createHelcimCustomer: vi.fn(),

tests/server/api/helcim-customer.test.js

@@ -12,6 +12,9 @@ import { createMockEvent } from '../helpers/createMockEvent.js'
 vi.mock('../../../server/models/member.js', () => ({
   default: { findOne: vi.fn(), create: vi.fn(), findByIdAndUpdate: vi.fn() }
 }))
+vi.mock('../../../server/models/preRegistration.js', () => ({
+  default: { findOne: vi.fn().mockResolvedValue(null), findByIdAndUpdate: vi.fn() }
+}))
 vi.mock('../../../server/utils/mongoose.js', () => ({ connectDB: vi.fn() }))
 vi.mock('../../../server/utils/helcim.js', () => ({
   createHelcimCustomer: vi.fn()