feat: differentiate fetch models error messages by failure type

Distinguish between missing API key, missing endpoint, auth failure,
unsupported provider (404/405), and timeout errors instead of showing
a generic failure toast for all cases.

src/lib/api/model-fetch.ts

@@ -1,4 +1,6 @@
 import { invoke } from "@tauri-apps/api/core";
+import type { TFunction } from "i18next";
+import { toast } from "sonner";
 
 export interface FetchedModel {
   id: string;
@@ -18,3 +20,49 @@ export async function fetchModelsForConfig(
 ): Promise<FetchedModel[]> {
   return invoke("fetch_models_for_config", { baseUrl, apiKey, isFullUrl });
 }
+
+/**
+ * 根据错误类型显示对应的 toast 提示
+ */
+export function showFetchModelsError(
+  err: unknown,
+  t: TFunction,
+  opts?: { hasApiKey: boolean; hasBaseUrl: boolean },
+): void {
+  // 前端预检：缺少必填字段
+  if (opts && !opts.hasBaseUrl && !opts.hasApiKey) {
+    toast.error(t("providerForm.fetchModelsNeedConfig"));
+    return;
+  }
+  if (opts && !opts.hasApiKey) {
+    toast.error(t("providerForm.fetchModelsNeedApiKey"));
+    return;
+  }
+  if (opts && !opts.hasBaseUrl) {
+    toast.error(t("providerForm.fetchModelsNeedEndpoint"));
+    return;
+  }
+
+  // 解析后端错误字符串
+  const msg = String(err);
+
+  if (msg.includes("HTTP 401") || msg.includes("HTTP 403")) {
+    toast.error(t("providerForm.fetchModelsAuthFailed"));
+    return;
+  }
+  if (msg.includes("HTTP 404") || msg.includes("HTTP 405")) {
+    toast.error(t("providerForm.fetchModelsNotSupported"));
+    return;
+  }
+  if (msg.includes("timeout") || msg.includes("timed out")) {
+    toast.error(t("providerForm.fetchModelsTimeout"));
+    return;
+  }
+  if (msg.includes("Failed to parse")) {
+    toast.error(t("providerForm.fetchModelsNotSupported"));
+    return;
+  }
+
+  // 通用兜底
+  toast.error(t("providerForm.fetchModelsFailed"));
+}