fix: normalize baseURL per protocol — auto-append /v1 if missing

@ai-sdk/anthropic expects baseURL to include /v1, but users often
configure without it. Now normalizeBaseUrl() handles all cases:
- https://xxx/api/coding → https://xxx/api/coding/v1 (appended)
- https://xxx/api/coding/v1 → unchanged
- https://xxx/api/coding/v1/ → trailing slash removed

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: deepracticexs

packages/routerx/src/app.ts

@@ -32,23 +32,49 @@ export interface RouterXConfig {
   apiKey?: string;
 }
 
+// ============================================================================
+// BaseURL normalization — each SDK expects a specific suffix
+// ============================================================================
+
+const PROTOCOL_BASE_SUFFIX: Record<string, string> = {
+  "openai-compatible": "/v1",
+  anthropic: "/v1",
+};
+
+const PROTOCOL_DEFAULT_BASE: Record<string, string> = {
+  "openai-compatible": "https://api.openai.com/v1",
+  anthropic: "https://api.anthropic.com/v1",
+};
+
+function normalizeBaseUrl(baseUrl: string, protocol: string): string {
+  const suffix = PROTOCOL_BASE_SUFFIX[protocol];
+  if (!suffix) return baseUrl;
+  const cleaned = baseUrl.replace(/\/+$/, "");
+  if (cleaned.endsWith(suffix)) return cleaned;
+  return cleaned + suffix;
+}
+
 // ============================================================================
 // Vercel AI SDK model factory
 // ============================================================================
 
 function createModel(provider: RegisteredProvider, modelId: string): LanguageModel {
+  const baseURL = provider.baseUrl
+    ? normalizeBaseUrl(provider.baseUrl, provider.protocol)
+    : PROTOCOL_DEFAULT_BASE[provider.protocol];
+
   switch (provider.protocol) {
     case "openai-compatible": {
       const p = createOpenAICompatible({
         name: provider.id,
-        baseURL: provider.baseUrl ?? "https://api.openai.com/v1",
+        baseURL,
         apiKey: provider.apiKey,
       });
       return p(modelId);
     }
     case "anthropic": {
       const p = createAnthropic({
-        baseURL: provider.baseUrl ?? "https://api.anthropic.com",
+        baseURL,
         apiKey: provider.apiKey,
       });
       return p(modelId);