Revert "feat(multi-session): allow to infer additional fields (#6585)"

This reverts commit 137863c.

Author: Bekacru

docs/content/docs/plugins/multi-session.mdx

@@ -102,15 +102,12 @@ type revokeDeviceSession = {
 
 When a user logs out, the plugin will revoke all active sessions for the user. You can do this by calling the existing `signOut` method, which handles revoking all sessions automatically.
 
-## Options
-
 ### Max Sessions
 
 You can specify the maximum number of sessions a user can have by passing the `maximumSessions` option to the plugin. By default, the plugin allows 5 sessions per device.
 
 ```ts title="auth.ts"
 import { betterAuth } from "better-auth"
-import { multiSession } from "better-auth/plugins"
 
 export const auth = betterAuth({
     plugins: [
@@ -119,59 +116,4 @@ export const auth = betterAuth({
         })
     ]
 })
-```
-
-### Additional Fields
-
-You can infer additional fields for the `user` and `session` schema by passing the `schema` option to both plugins.
-
-<Callout type="warning">
-    Note that this only affects type inference and does not modify the actual database schema.
-    Make sure that you [extend the core schema](/docs/concepts/database#extending-core-schema) accordingly.
-</Callout>
-
-```ts title="auth.ts"
-import { betterAuth } from "better-auth"
-import { multiSession } from "better-auth/plugins"
-
-export const auth = betterAuth({
-    plugins: [
-        multiSession({
-            schema: {
-                user: {
-                    additionalFields: {
-                        lang: {
-                            type: "string",
-                            required: false,
-                            defaultValue: "en"
-                        }
-                    }
-                }
-            }
-        })
-    ]
-})
-```
-
-```ts title="auth-client.ts"
-import { createAuthClient } from "better-auth/client"
-import { multiSessionClient } from "better-auth/client/plugins"
-
-export const authClient = createAuthClient({
-    plugins: [
-        multiSessionClient({
-            schema: {
-                user: {
-                    additionalFields: {
-                        lang: {
-                            type: "string",
-                            required: false,
-                            defaultValue: "en"
-                        }
-                    }
-                }
-            }
-        })
-    ]
-})
-```
+```

packages/better-auth/src/plugins/multi-session/client.ts

@@ -1,33 +1,13 @@
 import type { BetterAuthClientPlugin } from "@better-auth/core";
-import type { DBFieldAttribute } from "@better-auth/core/db";
 import type { multiSession } from ".";
 import { MULTI_SESSION_ERROR_CODES } from "./error-codes";
 
 export * from "./error-codes";
 
-export type MultiSessionClientOptions = {
-	schema?:
-		| {
-				user?:
-					| {
-							additionalFields?: Record<string, DBFieldAttribute> | undefined;
-					  }
-					| undefined;
-				session?:
-					| {
-							additionalFields?: Record<string, DBFieldAttribute> | undefined;
-					  }
-					| undefined;
-		  }
-		| undefined;
-};
-
-export const multiSessionClient = <O extends MultiSessionClientOptions>(
-	options?: O | undefined,
-) => {
+export const multiSessionClient = () => {
 	return {
 		id: "multi-session",
-		$InferServerPlugin: {} as ReturnType<typeof multiSession<O>>,
+		$InferServerPlugin: {} as ReturnType<typeof multiSession>,
 		atomListeners: [
 			{
 				matcher(path) {

packages/better-auth/src/plugins/multi-session/index.ts

@@ -3,6 +3,7 @@ import {
 	createAuthEndpoint,
 	createAuthMiddleware,
 } from "@better-auth/core/api";
+import { defineErrorCodes } from "@better-auth/core/utils";
 import * as z from "zod";
 import { APIError, sessionMiddleware } from "../../api";
 import {
@@ -21,9 +22,9 @@ export interface MultiSessionConfig {
 	maximumSessions?: number | undefined;
 }
 
-import { MULTI_SESSION_ERROR_CODES as ERROR_CODES } from "./error-codes";
-
-export { MULTI_SESSION_ERROR_CODES as ERROR_CODES } from "./error-codes";
+const ERROR_CODES = defineErrorCodes({
+	INVALID_SESSION_TOKEN: "Invalid session token",
+});
 
 const setActiveSessionBodySchema = z.object({
 	sessionToken: z.string().meta({