diff --git a/apps/web/lib/api.test.ts b/apps/web/lib/api.test.ts
new file mode 100644
index 0000000..f1e9fcb
--- /dev/null
+++ b/apps/web/lib/api.test.ts
@@ -0,0 +1,63 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { __resetApiAvailabilityForTests, api, resolveApiBase } from './api';
+
+test('API base defaults to same-origin in production and localhost in development', () => {
+  assert.equal(resolveApiBase({ NODE_ENV: 'production' }), '/api/v1');
+  assert.equal(resolveApiBase({ NODE_ENV: 'development' }), 'http://localhost:3001/api/v1');
+  assert.equal(
+    resolveApiBase({ NODE_ENV: 'production', NEXT_PUBLIC_API_URL: 'https://api.example.com/api/v1/' }),
+    'https://api.example.com/api/v1',
+  );
+});
+
+test('API requests use the resolved base path', async () => {
+  const originalFetch = globalThis.fetch;
+  const apiBase = resolveApiBase();
+  const urls: string[] = [];
+
+  globalThis.fetch = (async (input: RequestInfo | URL, init?: RequestInit) => {
+    urls.push(String(input));
+    return new Response(JSON.stringify(init?.method === 'POST' ? { ok: true } : {}), {
+      status: 200,
+      headers: { 'Content-Type': 'application/json' },
+    });
+  }) as typeof fetch;
+
+  try {
+    __resetApiAvailabilityForTests();
+    await api.post('/config/ai/test', { id: 'provider-1' });
+    assert.deepEqual(urls, [`${apiBase}/config/ai`, `${apiBase}/config/ai/test`]);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});
+
+test('API availability probe retries after a transient failure', async () => {
+  const originalFetch = globalThis.fetch;
+  const apiBase = resolveApiBase();
+  const calls: string[] = [];
+
+  globalThis.fetch = (async (input: RequestInfo | URL, init?: RequestInit) => {
+    calls.push(String(input));
+    if (calls.length === 1) throw new Error('temporary network failure');
+    return new Response(JSON.stringify(init?.method === 'POST' ? { ok: true } : {}), {
+      status: 200,
+      headers: { 'Content-Type': 'application/json' },
+    });
+  }) as typeof fetch;
+
+  try {
+    __resetApiAvailabilityForTests();
+    await assert.rejects(() => api.post('/config/ai/test', { id: 'provider-1' }), /API 不可用/);
+    await api.post('/config/ai/test', { id: 'provider-1' });
+    assert.deepEqual(calls, [
+      `${apiBase}/config/ai`,
+      `${apiBase}/config/ai`,
+      `${apiBase}/config/ai/test`,
+    ]);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});
diff --git a/apps/web/lib/api.ts b/apps/web/lib/api.ts
index b8b48e4..30a4e0c 100644
--- a/apps/web/lib/api.ts
+++ b/apps/web/lib/api.ts
@@ -1,4 +1,14 @@
-const API_BASE = process.env.NEXT_PUBLIC_API_URL || 'http://localhost:3001/api/v1';
+type ApiEnv = {
+  NEXT_PUBLIC_API_URL?: string;
+  NODE_ENV?: string;
+};
+
+export function resolveApiBase(env: ApiEnv = process.env) {
+  const fallback = env.NODE_ENV === 'production' ? '/api/v1' : 'http://localhost:3001/api/v1';
+  return (env.NEXT_PUBLIC_API_URL || fallback).replace(/\/$/, '');
+}
+
+const API_BASE = resolveApiBase();
 
 let apiAvailable: boolean | null = null;
 let probePromise: Promise<boolean> | null = null;
@@ -23,17 +33,19 @@ export class ApiRequestError extends Error {
 }
 
 async function checkApi(): Promise<boolean> {
-  if (apiAvailable !== null) return apiAvailable;
+  if (apiAvailable === true) return true;
   if (probePromise) return probePromise;
   probePromise = (async () => {
     try {
       // 探测一个不依赖数据库的端点（/config/ai 总是返回 200，只要 NestJS 起来了）
       const res = await fetch(`${API_BASE}/config/ai`, { method: 'GET', signal: AbortSignal.timeout(1500) });
-      apiAvailable = res.ok;
+      apiAvailable = res.ok ? true : null;
     } catch {
-      apiAvailable = false;
+      apiAvailable = null;
+    } finally {
+      probePromise = null;
     }
-    return apiAvailable;
+    return apiAvailable === true;
   })();
   return probePromise;
 }
@@ -45,7 +57,10 @@ async function request<T>(path: string, options?: RequestInit): Promise<T> {
     headers: { 'Content-Type': 'application/json', ...options?.headers },
     ...options,
   }).catch(() => null);
-  if (!res) throw new Error('API 不可用');
+  if (!res) {
+    apiAvailable = null;
+    throw new Error('API 不可用');
+  }
   if (!res.ok) {
     const error = await res.json().catch(() => ({}));
     throw new ApiRequestError(res.status, error);
@@ -83,3 +98,8 @@ export const api = {
     }
   },
 };
+
+export function __resetApiAvailabilityForTests() {
+  apiAvailable = null;
+  probePromise = null;
+}