From e1d22c1f64edb9688c952e1aee06d781e9a9d508 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adel=20Rodr=C3=ADguez?= <hello@adelrodriguez.com>
Date: Sun, 23 Aug 2026 11:13:56 -0400
Subject: [PATCH] fix: persist mobile sessions by matching the API auth cookie
 prefix

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 apps/api/src/shared/auth.ts      | 7 ++-----
 packages/auth/src/constants.ts   | 3 +++
 packages/auth/src/expo/client.ts | 6 +++++-
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/apps/api/src/shared/auth.ts b/apps/api/src/shared/auth.ts
index fa2e9ff3..c157f3e0 100644
--- a/apps/api/src/shared/auth.ts
+++ b/apps/api/src/shared/auth.ts
@@ -1,7 +1,7 @@
 import {
   AUTH_ADVANCED_OPTIONS,
+  AUTH_API_COOKIE_PREFIX,
   AUTH_APP_NAME,
-  AUTH_COOKIE_PREFIX,
   AUTH_EMAIL_AND_PASSWORD_OPTIONS,
   AUTH_SESSION_OPTIONS,
 } from "@init/auth/constants"
@@ -14,10 +14,7 @@ import { ENV } from "#shared/env.generated.ts"
 import { allowedOrigins, baseUrl } from "#shared/utils.ts"
 
 export const auth = createAuth({
-  // The app's auth instance shares the localhost cookie jar during
-  // development, so this instance namespaces its cookies to keep the two
-  // sessions from clobbering each other.
-  advanced: { ...AUTH_ADVANCED_OPTIONS, cookiePrefix: `${AUTH_COOKIE_PREFIX}-api` },
+  advanced: { ...AUTH_ADVANCED_OPTIONS, cookiePrefix: AUTH_API_COOKIE_PREFIX },
   appName: AUTH_APP_NAME,
   basePath: "/auth",
   baseURL: baseUrl,
diff --git a/packages/auth/src/constants.ts b/packages/auth/src/constants.ts
index 73a2b4ac..0148d4be 100644
--- a/packages/auth/src/constants.ts
+++ b/packages/auth/src/constants.ts
@@ -1,6 +1,9 @@
 import { seconds } from "humanspan"
 
 export const AUTH_COOKIE_PREFIX = "init"
+// The API's auth instance namespaces its cookies so the two localhost jars
+// stay separate during development.
+export const AUTH_API_COOKIE_PREFIX = `${AUTH_COOKIE_PREFIX}-api`
 export const AUTH_APP_NAME = "init"
 
 export const AUTH_ADVANCED_OPTIONS = {
diff --git a/packages/auth/src/expo/client.ts b/packages/auth/src/expo/client.ts
index a6572d74..dbff2127 100644
--- a/packages/auth/src/expo/client.ts
+++ b/packages/auth/src/expo/client.ts
@@ -1,8 +1,12 @@
 import { expoClient as baseExpoClient } from "@better-auth/expo/client"
-import { AUTH_COOKIE_PREFIX } from "#constants.ts"
+import { AUTH_API_COOKIE_PREFIX, AUTH_COOKIE_PREFIX } from "#constants.ts"
 
 export function expoClient(opts: Parameters<typeof baseExpoClient>[0]) {
   return baseExpoClient({
+    // Must match the API's cookie prefix: the Expo plugin only persists
+    // cookies whose names start with this value, and it defaults to
+    // "better-auth" when unset.
+    cookiePrefix: AUTH_API_COOKIE_PREFIX,
     scheme: AUTH_COOKIE_PREFIX,
     storagePrefix: AUTH_COOKIE_PREFIX,
     ...opts,