fix(library): 文章库导入失败时透传结构化 detail，恢复粘贴模式降级提示

frontend/src/composables/__tests__/useAuthFetch.spec.js

@@ -89,13 +89,37 @@ describe('useAuthFetch', () => {
     )
   })
 
-  it('对象 detail: stringify 而非 [object Object]', async () => {
+  it('对象 detail: hint/error 当作 message · 原对象挂到 err.detail', async () => {
+    fetchMock.mockResolvedValueOnce(
+      new Response(
+        JSON.stringify({ detail: { error: 'fetch_failed', hint: '抓取失败，请改用粘贴正文模式' } }),
+        { status: 400 }
+      )
+    )
+
+    const { authFetchJson } = useAuthFetch()
+    try {
+      await authFetchJson('/library/articles', { url: 'https://x.example' })
+      throw new Error('should have thrown')
+    } catch (err) {
+      expect(err.message).toBe('抓取失败，请改用粘贴正文模式')
+      expect(err.detail).toEqual({ error: 'fetch_failed', hint: '抓取失败，请改用粘贴正文模式' })
+    }
+  })
+
+  it('对象 detail 无 hint/error: 退回 JSON 串当 message · 仍挂 err.detail', async () => {
     fetchMock.mockResolvedValueOnce(
       new Response(JSON.stringify({ detail: { code: 'X', reason: 'Y' } }), { status: 500 })
     )
 
     const { authFetchJson } = useAuthFetch()
-    await expect(authFetchJson('/api/weird', {})).rejects.toThrow(/"code":"X"/)
+    try {
+      await authFetchJson('/api/weird', {})
+      throw new Error('should have thrown')
+    } catch (err) {
+      expect(err.message).toMatch(/"code":"X"/)
+      expect(err.detail).toEqual({ code: 'X', reason: 'Y' })
+    }
   })
 
   it('network 错误路径: 透传 fetch 抛出的错误', async () => {

frontend/src/composables/useAuthFetch.js

@@ -90,6 +90,7 @@ export function useAuthFetch() {
     })
     if (!resp.ok) {
       let detail = `HTTP ${resp.status}`
+      let structured = null
       try {
         const body = await resp.json()
         const raw = body?.detail ?? body?.error
@@ -100,12 +101,17 @@ export function useAuthFetch() {
           const parts = raw.map((d) => (d && typeof d === 'object' && d.msg) || JSON.stringify(d))
           if (parts.length) detail = parts.join('; ')
         } else if (raw != null && typeof raw === 'object') {
-          detail = JSON.stringify(raw)
+          // 结构化 detail（如 {error, hint}）：message 取 hint/error 作可读文案，
+          // 同时把原对象挂到 err.detail，让调用方能按业务字段降级处理
+          structured = raw
+          detail = raw.hint || raw.error || JSON.stringify(raw)
         }
       } catch {
         /* ignore parse error */
       }
-      throw new Error(detail)
+      const err = new Error(detail)
+      if (structured) err.detail = structured
+      throw err
     }
     return resp.json()
   }