refactor(schemas): extract nullable-default helpers to shared file

The three defensive Zod helpers (stringOrEmpty, numberOrZero,
booleanOrFalse) used by user.ts are general-purpose Zod utilities
that any schema may need — they're not user-specific. The original
inline declaration in user.ts had two downsides:

1. Any new schema (chat, auth, metrics, etc.) that needs the same
   'null | undefined → default scalar' pattern would have to
   duplicate the helper.

2. The long defensive-parse comment block (11 lines) lived inside
   user.ts and didn't explain the helpers' general purpose.

Move them to src/data/schemas/nullable-defaults.ts (top-level
sibling of auth/, chat/, metrics/, user/ subdirs) so any schema
can import them. Keep the original explanation verbatim at the
top of the new file.

Bundled in this commit:
- user.ts imports the helpers from the new file (drops 11 lines
  of comment + 3 const declarations)
- 3 auto-generated barrel index files regenerated by barrelsby
  to pick up the new exports (chat/, subscription/, stores/user/)

src/app/chat/components/index.ts

@@ -10,7 +10,6 @@ export * from "./chat-input-bar";
 export * from "./chat-input-text-field";
 export * from "./chat-quota-exhausted-banner";
 export * from "./chat-screen";
-
 export * from "./chat-send-button";
 export * from "./date-header";
 export * from "./fullscreen-image-viewer";

src/app/subscription/components/index.ts

@@ -5,7 +5,9 @@
 export * from "./subscription-back-link";
 export * from "./subscription-banner";
 export * from "./subscription-benefits-card";
+export * from "./subscription-checkout-button";
 export * from "./subscription-cta-button";
+export * from "./subscription-manage-button";
 export * from "./subscription-plan-card";
 export * from "./subscription-screen";
 export * from "./subscription-user-row";

src/data/schemas/nullable-defaults.ts

@@ -0,0 +1,33 @@
+/**
+ * Zod 默认值辅助器（处理 `null | undefined` → 标量默认）
+ *
+ * 防御性解析：后端对 Facebook / Apple 等 OAuth 用户可能返回 `null`（如 `email: null`），
+ * Zod 默认的 `.default("")` 只接受 `undefined`，遇到 `null` 会抛 ZodError → 登录静默失败。
+ * 用 `z.string().nullable().transform(v => v ?? "").default("")` 模式：
+ *   - input 接受 `string | null | undefined`（保持 optional）
+ *   - output 永远是 `string`（User 类的 `email: string` 声明不会破）
+ *
+ * 这是前端防御性解析（不要求后端修改）—— 和后端对齐更稳。
+ */
+import { z } from "zod";
+
+/** `string | null | undefined` → `string`（默认空串） */
+export const stringOrEmpty = z
+  .string()
+  .nullable()
+  .transform((v) => v ?? "")
+  .default("");
+
+/** `number | null | undefined` → `number`（默认 0） */
+export const numberOrZero = z
+  .number()
+  .nullable()
+  .transform((v) => v ?? 0)
+  .default(0);
+
+/** `boolean | null | undefined` → `boolean`（默认 false） */
+export const booleanOrFalse = z
+  .boolean()
+  .nullable()
+  .transform((v) => v ?? false)
+  .default(false);

src/data/schemas/user/user.ts

@@ -4,19 +4,11 @@
  */
 import { z } from "zod";
 import { PersonalityTraitsSchema, PERSONALITY_TRAITS_DEFAULTS } from "./personality_traits";
-
+import {
-/**
+  booleanOrFalse,
- * 防御性解析：后端对 Facebook / Apple 等 OAuth 用户可能返回 `null`（如 `email: null`），
+  numberOrZero,
- * Zod 默认的 `.default("")` 只接受 `undefined`，遇到 `null` 会抛 ZodError → 登录静默失败。
+  stringOrEmpty,
- * 用 `z.string().nullable().transform(v => v ?? "").default("")` 模式：
+} from "../nullable-defaults";
- *   - input 接受 `string | null | undefined`（保持 optional）
- *   - output 永远是 `string`（User 类的 `email: string` 声明不会破）
- *
- * 这是前端防御性解析（不要求后端修改）—— 和后端对齐更稳。
- */
-const stringOrEmpty = z.string().nullable().transform((v) => v ?? "").default("");
-const numberOrZero = z.number().nullable().transform((v) => v ?? 0).default(0);
-const booleanOrFalse = z.boolean().nullable().transform((v) => v ?? false).default(false);
 
 export const UserSchema = z.object({
   id: stringOrEmpty, // 兜底：理论 id 不会 null，但保持防御

src/stores/user/index.ts

@@ -4,5 +4,7 @@
 
 export * from "./user-context";
 export * from "./user-events";
+export * from "./user-machine.actors";
+export * from "./user-machine.helpers";
 export * from "./user-machine";
 export * from "./user-state";