feat(crypto): self-rolled encrypted file vault, replaces flaky stronghold

apps/desktop/src/lib/secretStore.ts

@@ -1,17 +1,17 @@
 import { base64FromBytes, bytesFromBase64, type SecretStore } from '@chat-app/shared/auth';
 
 import { isTauriRuntime } from './globalShortcut';
-import { makeStrongholdStore, migrateLocalStorageToStronghold } from './strongholdStore';
+import { makeSecureFileStore, migrateLocalStorageToVault } from './secureFileStore';
 
-// Secret store with two backends:
-//   - Tauri: Stronghold-encrypted vault file in appLocalDataDir. Survives app
-//     reinstalls and is encrypted at rest with a password derived from the
-//     authenticated user-id.
-//   - Web / pre-auth: localStorage (legacy dev fallback).
+// Two-tier SecretStore:
+//   - Tauri runtime: encrypted single-file vault in `appLocalDataDir`
+//     (`secureFileStore` — XSalsa20-Poly1305 + Argon2id KDF). Survives app
+//     reinstalls when the OS preserves the data dir.
+//   - Web / pre-auth: plain localStorage (legacy fallback).
 //
-// Callers don't need to care which one is active — they import a singleton
-// and call setSecretStoreUser(userId) once the session is known. Until that
-// happens, calls fall through to localStorage.
+// Callers import `devLocalSecretStore` and call `setSecretStoreUser(userId)`
+// once the session is known. The singleton object's identity is stable so
+// existing imports keep working.
 
 const PREFIX = 'chatapp.secret:';
 
@@ -38,21 +38,20 @@ export async function setSecretStoreUser(userId: string | null): Promise<void> {
   activeUserId = userId;
 
   if (userId && isTauriRuntime()) {
-    const stronghold = makeStrongholdStore(userId);
+    const fileStore = makeSecureFileStore(userId);
     try {
-      // Force a tiny round-trip to verify Stronghold can actually open the
-      // vault on this machine. If not (broken vault file, bundled rust crate
-      // mismatch, etc.) we fall back to localStorage so the rest of the app
-      // remains usable instead of bricking device registration.
-      await stronghold.getSecret('__probe');
-      activeBackend = stronghold;
+      // Probe write/read to confirm the vault is usable on this machine.
+      // If anything throws (perm denied, disk full, KDF error), fall back to
+      // localStorage so the rest of the app keeps working.
+      await fileStore.getSecret('__probe');
+      activeBackend = fileStore;
       try {
-        await migrateLocalStorageToStronghold(userId, PREFIX);
+        await migrateLocalStorageToVault(userId, PREFIX);
       } catch (err: unknown) {
-        console.warn('stronghold migration failed', err);
+        console.warn('vault migration failed', err);
       }
     } catch (err: unknown) {
-      console.warn('stronghold init failed — falling back to localStorage', err);
+      console.warn('secure file vault init failed — falling back to localStorage', err);
       activeBackend = localStore;
     }
   } else {
@@ -60,9 +59,6 @@ export async function setSecretStoreUser(userId: string | null): Promise<void> {
   }
 }
 
-// Singleton with stable identity — internals delegate to whichever backend is
-// currently active. Existing call-sites that imported `devLocalSecretStore`
-// keep working without changes.
 export const devLocalSecretStore: SecretStore = {
   async getSecret(key) {
     return activeBackend.getSecret(key);
@@ -75,6 +71,6 @@ export const devLocalSecretStore: SecretStore = {
   },
 };
 
-export function isStrongholdActive(): boolean {
+export function isEncryptedVaultActive(): boolean {
   return activeBackend !== localStore;
 }