feat: implement TASK-WP1-01 registration transaction

apps/api/src/resend-adapter.ts

@@ -0,0 +1,25 @@
+export interface RegistrationCodeMessage {
+  challengeId: string;
+  code: string;
+  email: string;
+  purpose: "register";
+}
+
+export interface ResendAdapter {
+  sendRegistrationCode(message: RegistrationCodeMessage): Promise<void>;
+}
+
+export class MockResendAdapter implements ResendAdapter {
+  readonly calls: RegistrationCodeMessage[] = [];
+
+  async sendRegistrationCode(message: RegistrationCodeMessage) {
+    this.calls.push({ ...message });
+  }
+
+  readLatestCode(email: string) {
+    const normalizedEmail = email.trim().toLowerCase();
+    const call = this.calls.findLast((candidate) => candidate.email === normalizedEmail);
+    if (!call) throw new Error("No mock registration message exists for that email.");
+    return call.code;
+  }
+}