fix(mobile): address Apple review onboarding flows

apps/mobile/src/lib/appleProfileNamePersistence.ts

@@ -0,0 +1,36 @@
+import type { Profile } from '../types';
+
+export interface AppleProfileNameSession {
+    userId: string;
+    accessToken: string;
+}
+
+export interface AppleProfileNamePersistenceDependencies {
+    getProfile: (accessToken: string) => Promise<{ profile: Pick<Profile, 'id' | 'name'> }>;
+    updateProfileName: (accessToken: string, name: string) => Promise<unknown>;
+}
+
+export type AppleProfileNamePersistenceResult = 'updated' | 'existing';
+
+/**
+ * Persist a first-authorization Apple display name only for the exact subject
+ * and bearer that completed the authorization. The profile read protects an
+ * existing Sauci nickname from being overwritten.
+ */
+export async function persistAppleProfileName(
+    session: AppleProfileNameSession,
+    name: string,
+    dependencies: AppleProfileNamePersistenceDependencies,
+): Promise<AppleProfileNamePersistenceResult> {
+    const { profile } = await dependencies.getProfile(session.accessToken);
+    if (profile.id !== session.userId) {
+        throw new Error('Apple profile subject did not match the authenticated user');
+    }
+
+    if (profile.name?.trim()) {
+        return 'existing';
+    }
+
+    await dependencies.updateProfileName(session.accessToken, name);
+    return 'updated';
+}