fix(desktop): collect + persist API key for custom OpenAI endpoints (#43896)

The desktop "Local / custom endpoint" onboarding never collected an API
key and /api/model/set silently dropped one, so an auth-gated endpoint
(e.g. a hosted vLLM behind a key) could never enumerate models — and
Settings' "Set up custom endpoint" routed `custom` into a non-existent
OAuth flow, booting the user back to the first screen (the reported loop).

Backend (web_server.py):
- /api/providers/validate accepts an optional api_key and sends it as a
  Bearer header when probing a custom endpoint's /v1/models.
- /api/model/set accepts api_key, persists it to model.api_key (same
  switch/preserve lifecycle as base_url), and registers a named
  custom_providers entry via _save_custom_provider — matching the
  `hermes model` CLI flow so the endpoint shows up as a ready picker row.

Desktop:
- ApiKeyForm shows an optional API key field for the local/custom option;
  the key is threaded through saveOnboardingLocalEndpoint → validate +
  setModelAssignment.
- New onboarding `localEndpoint` intent + startManualLocalEndpoint(); the
  Settings "Set up custom endpoint" button now opens the local-endpoint
  form (URL + key) instead of the OAuth dead-end.
- Added localApiKeyPlaceholder i18n key (en + types + zh).

Tests: api_key lifecycle on _apply_main_model_assignment, key persistence
+ custom_providers registration on /api/model/set, Bearer-header probe;
onboarding store forwards + persists the key.

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

@@ -26,7 +26,8 @@ function setProviders(providers: OAuthProvider[]) {
     reason: null,
     requested: false,
     firstRunSkipped: false,
-    manual: false
+    manual: false,
+    localEndpoint: false
   } satisfies DesktopOnboardingState)
 }
 
@@ -49,7 +50,8 @@ afterEach(() => {
     reason: null,
     requested: false,
     firstRunSkipped: false,
-    manual: false
+    manual: false,
+    localEndpoint: false
   })
 })
 

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

@@ -430,19 +430,24 @@ const persistShowAll = (value: boolean) => {
 
 export function Picker({ ctx }: { ctx: OnboardingContext }) {
   const { t } = useI18n()
-  const { manual, mode, providers } = useStore($desktopOnboarding)
+  const { localEndpoint, manual, mode, providers } = useStore($desktopOnboarding)
   const [showAll, setShowAll] = useState(readShowAll)
   const ordered = useMemo(() => (providers ? sortProviders(providers) : []), [providers])
   const hasOauth = ordered.length > 0
   const apiKeyOptions = useApiKeyCatalog()
 
-  if (mode === 'apikey' || !hasOauth) {
+  // localEndpoint forces the key form regardless of `mode` (which a manual
+  // provider refresh may flip back to 'oauth'); it preselects the local option
+  // and hides the "back to sign in" link since the user came specifically to
+  // configure a custom endpoint.
+  if (localEndpoint || mode === 'apikey' || !hasOauth) {
     return (
       <div className="grid gap-3">
         <ApiKeyForm
-          canGoBack={hasOauth}
+          canGoBack={hasOauth && !localEndpoint}
+          initialEnvKey={localEndpoint ? 'OPENAI_BASE_URL' : undefined}
           onBack={() => setOnboardingMode('oauth')}
-          onSave={(envKey, value, name) => saveOnboardingApiKey(envKey, value, name, ctx)}
+          onSave={(envKey, value, name, apiKey) => saveOnboardingApiKey(envKey, value, name, ctx, apiKey)}
           options={apiKeyOptions}
         />
         {manual ? null : (
@@ -630,6 +635,7 @@ export function ProviderRow({
 // surfaces render the identical form.
 export function ApiKeyForm({
   canGoBack,
+  initialEnvKey,
   isSet,
   onBack,
   onClear,
@@ -638,16 +644,31 @@ export function ApiKeyForm({
   redactedValue
 }: {
   canGoBack: boolean
+  /** Preselect a specific option by env key (e.g. 'OPENAI_BASE_URL' to land on
+   *  the local / custom endpoint form). Falls back to the first option. */
+  initialEnvKey?: string
   isSet?: (envKey: string) => boolean
   onBack: () => void
   onClear?: (envKey: string) => void
-  onSave: (envKey: string, value: string, name: string) => Promise<{ message?: string; ok: boolean }>
+  onSave: (
+    envKey: string,
+    value: string,
+    name: string,
+    apiKey?: string
+  ) => Promise<{ message?: string; ok: boolean }>
   options?: ApiKeyOption[]
   redactedValue?: (envKey: string) => null | string | undefined
 }) {
   const { t } = useI18n()
-  const [option, setOption] = useState<ApiKeyOption>(options[0])
+
+  const [option, setOption] = useState<ApiKeyOption>(
+    () => options.find(o => o.envKey === initialEnvKey) ?? options[0]
+  )
+
   const [value, setValue] = useState('')
+  // Optional endpoint API key, only used by the local / custom endpoint option
+  // (whose `value` is the base URL). Cleared whenever the option changes.
+  const [localKey, setLocalKey] = useState('')
   const [saving, setSaving] = useState(false)
   const [error, setError] = useState<null | string>(null)
   // `options` can change at runtime when callers filter the catalog (e.g. the
@@ -657,6 +678,7 @@ export function ApiKeyForm({
     if (options.length > 0 && !options.some(o => o.envKey === option.envKey)) {
       setOption(options[0])
       setValue('')
+      setLocalKey('')
       setError(null)
     }
   }, [option.envKey, options])
@@ -668,6 +690,7 @@ export function ApiKeyForm({
   const pick = (o: ApiKeyOption) => {
     setOption(o)
     setValue('')
+    setLocalKey('')
     setError(null)
     requestAnimationFrame(() => {
       entryRef.current?.scrollIntoView({ behavior: 'smooth', block: 'center' })
@@ -693,10 +716,11 @@ export function ApiKeyForm({
 
     setSaving(true)
     setError(null)
-    const result = await onSave(option.envKey, value, option.name)
+    const result = await onSave(option.envKey, value, option.name, isLocal ? localKey : undefined)
 
     if (result.ok) {
       setValue('')
+      setLocalKey('')
     } else {
       setError(result.message ?? t.onboarding.couldNotSave)
     }
@@ -759,6 +783,17 @@ export function ApiKeyForm({
           type={isLocal ? 'text' : 'password'}
           value={value}
         />
+        {isLocal ? (
+          <Input
+            autoComplete="off"
+            className="font-mono"
+            onChange={e => setLocalKey(e.target.value)}
+            onKeyDown={e => e.key === 'Enter' && void submit()}
+            placeholder={t.onboarding.localApiKeyPlaceholder}
+            type="password"
+            value={localKey}
+          />
+        ) : null}
         {error ? <p className="text-xs text-destructive">{error}</p> : null}
       </div>
 

apps/desktop/src/components/gateway-connecting-overlay.test.tsx

@@ -41,7 +41,8 @@ function resetStores() {
     reason: null,
     requested: false,
     firstRunSkipped: false,
-    manual: false
+    manual: false,
+    localEndpoint: false
   })
 }