feat(vault): vault storage (user-isolated, multi-account)

src/config/index.ts

@@ -67,9 +67,9 @@ export const API_ENDPOINTS = {
 // =============================================================================
 // Vault storage (user-isolated, multi-account)
 // =============================================================================
-// - AsyncStorage keys for vault state (S0 share, initialized flag).
-// - User-scoped: each account has its own keys so vault state is isolated.
-// - Store: use getVaultStorageKeys(userId) and write to INITIALIZED / SHARE_DEVICE.
+// - AsyncStorage keys for vault state (S0 share, initialized flag, mnemonic part backup).
+// - User-scoped: each account has its own keys so vault/mnemonic state is isolated.
+// - Store: use getVaultStorageKeys(userId) and write to INITIALIZED / SHARE_DEVICE / MNEMONIC_PART_LOCAL.
 // - Clear: use same keys in multiRemove (e.g. MeScreen Reset Vault State).
 // - Multi-account: same device, multiple users → each has independent vault (no cross-user leakage).
 
@@ -79,21 +79,24 @@ const VAULT_KEY_PREFIX = 'sentinel_vault';
 export const VAULT_STORAGE_KEYS = {
   INITIALIZED: 'sentinel_vault_initialized',
   SHARE_DEVICE: 'sentinel_vault_s0',
+  MNEMONIC_PART_LOCAL: 'sentinel_mnemonic_part_local',
 } as const;
 
 /**
  * Returns vault storage keys for the given user (user isolation).
- * - Use for: reading S0, writing S0 after mnemonic, clearing on Reset Vault State.
+ * - Use for: reading/writing S0, mnemonic part backup, clearing on Reset Vault State.
  * - userId null → guest namespace (_guest). userId set → per-user namespace (_u{userId}).
  */
 export function getVaultStorageKeys(userId: number | string | null): {
   INITIALIZED: string;
   SHARE_DEVICE: string;
+  MNEMONIC_PART_LOCAL: string;
 } {
   const suffix = userId != null ? `_u${userId}` : '_guest';
   return {
     INITIALIZED: `${VAULT_KEY_PREFIX}_initialized${suffix}`,
     SHARE_DEVICE: `${VAULT_KEY_PREFIX}_s0${suffix}`,
+    MNEMONIC_PART_LOCAL: `sentinel_mnemonic_part_local${suffix}`,
   };
 }
 

src/screens/MeScreen.tsx

@@ -315,6 +315,7 @@ export default function MeScreen() {
       await AsyncStorage.multiRemove([
         vaultKeys.INITIALIZED,
         vaultKeys.SHARE_DEVICE,
+        vaultKeys.MNEMONIC_PART_LOCAL,
       ]);
       setResetVaultFeedback({
         status: 'success',

src/screens/VaultScreen.tsx

@@ -258,7 +258,7 @@ export default function VaultScreen() {
     setProgressIndex(0);
     progressAnim.setValue(0);
     setTimeout(() => setShowMnemonic(true), 200);
-    AsyncStorage.setItem('sentinel_mnemonic_part_local', parts[0].join(' ')).catch(() => {
+    AsyncStorage.setItem(vaultKeys.MNEMONIC_PART_LOCAL, parts[0].join(' ')).catch(() => {
       // Best-effort local store; UI remains available
     });
   };