fix(desktop): structured Fallback Models editor

Settings → Model rendered `fallback_providers` (a list of `{provider,
model}` objects) through the generic `list` config field, which does
`value.join(', ')` and stringified each entry to `[object Object],
[object Object]`.

Add a dedicated provider+model row editor (add/remove), sourced from the
same `getGlobalModelOptions()` the composer picker uses, that reads and
writes the `{provider, model}` chain. Half-filled rows are kept in local
state so the config autosave never persists a partial entry, and an
out-of-catalog model stays selectable so existing custom entries render.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/desktop/src/app/settings/config-settings.tsx

@@ -19,6 +19,7 @@ import { useOnProfileSwitch } from '../hooks/use-on-profile-switch'
 import { PanelEmpty } from '../overlays/panel'
 
 import { CONTROL_TEXT, EMPTY_SELECT_VALUE, FIELD_DESCRIPTIONS, FIELD_LABELS, SECTIONS } from './constants'
+import { FallbackModelsField } from './fallback-models-field'
 import { fieldCopyForSchemaKey } from './field-copy'
 import { enumOptionsFor, getNested, prettyName, setNested } from './helpers'
 import { MemoryConnect } from './memory/connect'
@@ -100,6 +101,13 @@ function ConfigField({
     <ListRow action={action} description={descriptionNode} title={label} wide={wide} />
   )
 
+  // `fallback_providers` is a list of {provider, model} objects; the generic
+  // `list` branch below would stringify them to "[object Object]". Render the
+  // dedicated structured editor instead.
+  if (schemaKey === 'fallback_providers') {
+    return row(<FallbackModelsField onChange={onChange} value={value} />, true)
+  }
+
   if (schema.type === 'boolean') {
     return row(
       <div className="flex items-center justify-end">

apps/desktop/src/app/settings/fallback-models-field.tsx

@@ -0,0 +1,137 @@
+import { useQuery } from '@tanstack/react-query'
+import { useState } from 'react'
+
+import { Button } from '@/components/ui/button'
+import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from '@/components/ui/select'
+import { getGlobalModelOptions } from '@/hermes'
+import { useI18n } from '@/i18n'
+import { Plus, X } from '@/lib/icons'
+import { cn } from '@/lib/utils'
+
+import { CONTROL_TEXT } from './constants'
+
+interface FallbackEntry {
+  provider: string
+  model: string
+}
+
+// Normalize the raw config value (`fallback_providers`: a list of
+// `{provider, model}` dicts) into editor rows. Defensive against legacy string
+// entries ("provider/model") so the editor never crashes on odd data.
+function normalizeEntries(value: unknown): FallbackEntry[] {
+  if (!Array.isArray(value)) {
+    return []
+  }
+
+  return value.map(item => {
+    if (item && typeof item === 'object') {
+      const record = item as Record<string, unknown>
+
+      return { provider: String(record.provider ?? ''), model: String(record.model ?? '') }
+    }
+
+    if (typeof item === 'string') {
+      const slash = item.indexOf('/')
+
+      return slash > 0 ? { provider: item.slice(0, slash), model: item.slice(slash + 1) } : { provider: '', model: item }
+    }
+
+    return { provider: '', model: '' }
+  })
+}
+
+/**
+ * Structured editor for the top-level `fallback_providers` config list — a
+ * chain of `{provider, model}` pairs tried in order when the default model
+ * fails. Replaces the generic comma-string `list` input, which stringified the
+ * objects to "[object Object], [object Object]".
+ *
+ * Mirrors the Auxiliary Models picker in `model-settings.tsx`: provider + model
+ * selects sourced from `getGlobalModelOptions()`. Half-filled rows are kept in
+ * local state and only complete pairs are emitted upward, so the config
+ * autosave never persists a partial `{provider, model: ''}`.
+ */
+export function FallbackModelsField({
+  value,
+  onChange
+}: {
+  value: unknown
+  onChange: (next: FallbackEntry[]) => void
+}) {
+  const { t } = useI18n()
+  const m = t.settings.model
+
+  const modelOptions = useQuery({
+    queryKey: ['model-options', 'global'],
+    queryFn: () => getGlobalModelOptions()
+  })
+
+  const providers = (modelOptions.data?.providers ?? []).filter(provider => provider.slug)
+
+  const [rows, setRows] = useState<FallbackEntry[]>(() => normalizeEntries(value))
+
+  const commit = (next: FallbackEntry[]) => {
+    setRows(next)
+    onChange(next.filter(entry => entry.provider && entry.model))
+  }
+
+  const updateRow = (index: number, patch: Partial<FallbackEntry>) =>
+    commit(rows.map((entry, i) => (i === index ? { ...entry, ...patch } : entry)))
+
+  return (
+    <div className="grid w-full gap-1.5">
+      {rows.length === 0 && <p className="text-xs text-muted-foreground">{m.fallbackEmpty}</p>}
+      {rows.map((entry, index) => {
+        const providerRow = providers.find(provider => provider.slug === entry.provider)
+        const catalog = providerRow?.models ?? []
+        // Keep an out-of-catalog model selectable so an existing custom
+        // provider/model renders instead of showing a blank box.
+        const modelItems = entry.model && !catalog.includes(entry.model) ? [entry.model, ...catalog] : catalog
+
+        return (
+          <div className="flex flex-wrap items-center gap-2" key={index}>
+            <span className="w-4 shrink-0 text-center font-mono text-[0.7rem] text-muted-foreground">{index + 1}</span>
+            <Select onValueChange={provider => updateRow(index, { provider, model: '' })} value={entry.provider}>
+              <SelectTrigger className={cn('min-w-36', CONTROL_TEXT)}>
+                <SelectValue placeholder={m.provider} />
+              </SelectTrigger>
+              <SelectContent>
+                {providers.map(provider => (
+                  <SelectItem key={provider.slug} value={provider.slug}>
+                    {provider.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+            <Select onValueChange={model => updateRow(index, { model })} value={entry.model}>
+              <SelectTrigger className={cn('min-w-52 flex-1', CONTROL_TEXT)}>
+                <SelectValue placeholder={m.model} />
+              </SelectTrigger>
+              <SelectContent>
+                {modelItems.map(model => (
+                  <SelectItem key={model} value={model}>
+                    {model}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+            <Button
+              aria-label={t.common.remove}
+              onClick={() => commit(rows.filter((_, i) => i !== index))}
+              size="icon-xs"
+              variant="ghost"
+            >
+              <X className="size-3.5" />
+            </Button>
+          </div>
+        )
+      })}
+      <div>
+        <Button onClick={() => commit([...rows, { provider: '', model: '' }])} size="sm" variant="textStrong">
+          <Plus className="size-3.5" />
+          {m.fallbackAdd}
+        </Button>
+      </div>
+    </div>
+  )
+}

apps/desktop/src/i18n/en.ts

@@ -707,6 +707,9 @@ export const en: Translations = {
       change: 'Change',
       autoUseMain: 'auto · use main model',
       providerDefault: '(provider default)',
+      fallbackAdd: 'Add fallback',
+      fallbackEmpty: 'No fallback models — the default model is used unless it fails.',
+      notInCatalog: "isn't in this provider's model list — calls may fall back to a backup.",
       tasks: {
         vision: { label: 'Vision', hint: 'Image analysis' },
         web_extract: { label: 'Web extract', hint: 'Page summarization' },

apps/desktop/src/i18n/types.ts

@@ -611,6 +611,9 @@ export interface Translations {
       change: string
       autoUseMain: string
       providerDefault: string
+      fallbackAdd: string
+      fallbackEmpty: string
+      notInCatalog: string
       tasks: Record<string, AuxTaskCopy>
     }
     providers: {

apps/desktop/src/i18n/zh.ts

@@ -895,6 +895,9 @@ export const zh: Translations = {
       change: '更改',
       autoUseMain: '自动 · 使用主模型',
       providerDefault: '(提供方默认)',
+      fallbackAdd: '添加备用模型',
+      fallbackEmpty: '未配置备用模型 — 默认模型失败时才会使用备用模型。',
+      notInCatalog: '不在该提供方的模型列表中 — 调用可能回退到备用模型。',
       tasks: {
         vision: { label: '视觉', hint: '图片分析' },
         web_extract: { label: '网页提取', hint: '页面总结' },