feat(desktop): make xAI Grok a first-class OAuth provider in the launcher

xAI Grok was only reachable via the "I have an API key" form. xAI's
OAuth (SuperGrok / Premium+) flow already exists in the backend
(`hermes auth add xai-oauth`) but was never surfaced in the desktop
onboarding launcher.

Add a loopback PKCE flow: the local backend binds the 127.0.0.1
callback listener, the client opens the browser, and the redirect lands
back automatically — no code to copy/paste. Reuses the existing xAI
OAuth helpers (discovery, callback server, token exchange, persist)
rather than duplicating them.

- web_server: catalog entry (flow: loopback) + status dispatch +
  _start_xai_loopback_flow + background worker + route branch
- desktop: 'loopback' flow type, awaiting_browser status, xAI Grok card
  (PROVIDER_DISPLAY / FLOW_SUBTITLES / FlowPanel waiting render)
- tests: catalog listing, start authorize-url, worker persist, state
  mismatch rejection

apps/desktop/src/components/desktop-onboarding-overlay.tsx

@@ -107,8 +107,9 @@ const PROVIDER_DISPLAY: Record<string, { order: number; title: string }> = {
   anthropic: { order: 1, title: 'Anthropic Claude' },
   'openai-codex': { order: 2, title: 'OpenAI Codex / ChatGPT' },
   'minimax-oauth': { order: 3, title: 'MiniMax' },
-  'claude-code': { order: 4, title: 'Claude Code' },
-  'qwen-oauth': { order: 5, title: 'Qwen Code' }
+  'xai-oauth': { order: 4, title: 'xAI Grok' },
+  'claude-code': { order: 5, title: 'Claude Code' },
+  'qwen-oauth': { order: 6, title: 'Qwen Code' }
 }
 
 const assetPath = (path: string) => `${import.meta.env.BASE_URL}${path.replace(/^\/+/, '')}`
@@ -116,6 +117,7 @@ const assetPath = (path: string) => `${import.meta.env.BASE_URL}${path.replace(/
 const FLOW_SUBTITLES: Record<OAuthProvider['flow'], string> = {
   pkce: 'Opens your browser to sign in, then continues here',
   device_code: 'Opens a verification page in your browser — Hermes connects automatically',
+  loopback: 'Opens your browser to sign in — Hermes connects automatically',
   external: 'Sign in once in your terminal, then come back to chat'
 }
 
@@ -565,6 +567,24 @@ function FlowPanel({ ctx, flow }: { ctx: OnboardingContext; flow: OnboardingFlow
     )
   }
 
+  if (flow.status === 'awaiting_browser') {
+    return (
+      <Step title={`Sign in with ${title}`}>
+        <p className="text-sm text-muted-foreground">
+          We opened {title} in your browser. Authorize Hermes there and you'll be connected
+          automatically — nothing to copy or paste.
+        </p>
+        <FlowFooter left={<DocsLink href={flow.start.auth_url}>Re-open sign-in page</DocsLink>}>
+          <span className="flex items-center gap-2 text-xs text-muted-foreground">
+            <Loader2 className="size-3 animate-spin" />
+            Waiting for you to authorize...
+          </span>
+          <CancelBtn size="sm" />
+        </FlowFooter>
+      </Step>
+    )
+  }
+
   if (flow.status === 'external_pending') {
     return (
       <Step title={`Sign in with ${title}`}>

apps/desktop/src/store/onboarding.ts

@@ -18,6 +18,7 @@ import type { ModelOptionProvider, OAuthProvider, OAuthStartResponse } from '@/t
 
 type PkceStart = Extract<OAuthStartResponse, { flow: 'pkce' }>
 type DeviceStart = Extract<OAuthStartResponse, { flow: 'device_code' }>
+type LoopbackStart = Extract<OAuthStartResponse, { flow: 'loopback' }>
 
 export type OnboardingMode = 'apikey' | 'oauth'
 
@@ -26,6 +27,10 @@ export type OnboardingFlow =
   | { provider: OAuthProvider; status: 'starting' }
   | { code: string; provider: OAuthProvider; start: PkceStart; status: 'awaiting_user' }
   | { copied: boolean; provider: OAuthProvider; start: DeviceStart; status: 'polling' }
+  // Loopback PKCE (xAI Grok): browser opens, the local backend's 127.0.0.1
+  // listener catches the redirect, and we poll until the worker finishes.
+  // No code to paste and no user_code to show — just a waiting state.
+  | { provider: OAuthProvider; start: LoopbackStart; status: 'awaiting_browser' }
   | { provider: OAuthProvider; start: OAuthStartResponse; status: 'submitting' }
   | { copied: boolean; provider: OAuthProvider; status: 'external_pending' }
   | { provider: OAuthProvider; status: 'success' }
@@ -419,7 +424,8 @@ export async function startProviderOAuth(provider: OAuthProvider, ctx: Onboardin
 
   try {
     const start = await startOAuthLogin(provider.id)
-    await window.hermesDesktop?.openExternal(start.flow === 'pkce' ? start.auth_url : start.verification_url)
+    const browserUrl = start.flow === 'device_code' ? start.verification_url : start.auth_url
+    await window.hermesDesktop?.openExternal(browserUrl)
 
     if (start.flow === 'pkce') {
       setFlow({ status: 'awaiting_user', provider, start, code: '' })
@@ -427,14 +433,26 @@ export async function startProviderOAuth(provider: OAuthProvider, ctx: Onboardin
       return
     }
 
+    if (start.flow === 'loopback') {
+      // No code to paste: the redirect lands on the backend's loopback
+      // listener. Just wait and poll the session until the worker finishes.
+      setFlow({ status: 'awaiting_browser', provider, start })
+      pollTimer = window.setInterval(() => void pollSession(provider, start, ctx), POLL_MS)
+
+      return
+    }
+
     setFlow({ status: 'polling', provider, start, copied: false })
-    pollTimer = window.setInterval(() => void pollDevice(provider, start, ctx), POLL_MS)
+    pollTimer = window.setInterval(() => void pollSession(provider, start, ctx), POLL_MS)
   } catch (error) {
     setFlow({ status: 'error', provider, message: `Could not start sign-in: ${errMessage(error)}` })
   }
 }
 
-async function pollDevice(provider: OAuthProvider, start: DeviceStart, ctx: OnboardingContext) {
+// Poll a session-backed flow (device_code or loopback) until it resolves.
+// Both shapes only need the session_id to poll; the start is threaded
+// through to the error flow so the user can retry from the same context.
+async function pollSession(provider: OAuthProvider, start: DeviceStart | LoopbackStart, ctx: OnboardingContext) {
   try {
     const { error_message, status } = await pollOAuthSession(provider.id, start.session_id)
 

apps/desktop/src/types/hermes.ts

@@ -48,7 +48,7 @@ export interface OAuthProviderStatus {
 export interface OAuthProvider {
   cli_command: string
   docs_url: string
-  flow: 'device_code' | 'external' | 'pkce'
+  flow: 'device_code' | 'external' | 'loopback' | 'pkce'
   id: string
   name: string
   status: OAuthProviderStatus
@@ -73,6 +73,12 @@ export type OAuthStartResponse =
       user_code: string
       verification_url: string
     }
+  | {
+      auth_url: string
+      expires_in: number
+      flow: 'loopback'
+      session_id: string
+    }
 
 export interface OAuthSubmitResponse {
   message?: string