refactor: Remove init_token handling from admin initialization logic and related tests

frontend/src/app/(auth)/setup/page.tsx

@@ -26,9 +26,6 @@ export default function SetupPage() {
   const [error, setError] = useState("");
   const [loading, setLoading] = useState(false);
 
-  // --- Init-admin mode only ---
-  const [initToken, setInitToken] = useState("");
-
   // --- Change-password mode only ---
   const [currentPassword, setCurrentPassword] = useState("");
 
@@ -82,7 +79,6 @@ export default function SetupPage() {
         body: JSON.stringify({
           email,
           password: newPassword,
-          init_token: initToken,
         }),
       });
 
@@ -190,23 +186,6 @@ export default function SetupPage() {
                 required
               />
             </div>
-            <div className="flex flex-col space-y-1">
-              <label htmlFor="initToken" className="text-sm font-medium">
-                Initialization Token
-              </label>
-              <Input
-                id="initToken"
-                type="text"
-                placeholder="Copy from server startup logs"
-                value={initToken}
-                onChange={(e) => setInitToken(e.target.value)}
-                required
-                autoComplete="off"
-              />
-              <p className="text-muted-foreground text-xs">
-                Find the <code>INIT TOKEN</code> printed in the server startup logs.
-              </p>
-            </div>
             <div className="flex flex-col space-y-1">
               <label htmlFor="password" className="text-sm font-medium">
                 Password

frontend/src/core/auth/types.ts

@@ -40,7 +40,6 @@ const AUTH_ERROR_CODES = [
   "provider_not_found",
   "not_authenticated",
   "system_already_initialized",
-  "invalid_init_token",
 ] as const;
 
 export type AuthErrorCode = (typeof AUTH_ERROR_CODES)[number];

frontend/src/core/threads/hooks.ts

@@ -322,7 +322,7 @@ export function useThreadStream({
   useEffect(() => {
     if (
       optimisticMessages.length > 0 &&
-      thread.messages.length > prevMsgCountRef.current
+      thread.messages.length > prevMsgCountRef.current + 1
     ) {
       setOptimisticMessages([]);
     }