Stabilize API routing, CORS, and settings save behavior

frontend/src/lib/api.test.ts

@@ -97,11 +97,11 @@ async function runApiTests(): Promise<void> {
     assert(await thumbnail.text() === 'preview-bytes', 'Thumbnail blob bytes mismatch');
     assert(await preview.text() === 'preview-bytes', 'Preview blob bytes mismatch');
     assert(
-      requestUrls[0] === '/api/v1/documents/doc-1/thumbnail',
+      requestUrls[0] === 'http://localhost:8000/api/v1/documents/doc-1/thumbnail',
       `Unexpected thumbnail URL ${requestUrls[0]}`,
     );
     assert(
-      requestUrls[1] === '/api/v1/documents/doc-1/preview',
+      requestUrls[1] === 'http://localhost:8000/api/v1/documents/doc-1/preview',
       `Unexpected preview URL ${requestUrls[1]}`,
     );
     assert(requestAuthHeaders[0] === null, `Expected no auth header for thumbnail request, got "${requestAuthHeaders[0]}"`);

frontend/src/lib/api.ts

@@ -14,7 +14,7 @@ import type {
 } from '../types';
 
 /**
- * Resolves backend base URL from environment with same-origin proxy fallback.
+ * Resolves backend base URL from environment with host-derived HTTP fallback.
  */
 function resolveApiBase(): string {
   const envValue = import.meta.env?.VITE_API_BASE;
@@ -25,7 +25,10 @@ function resolveApiBase(): string {
     }
   }
 
-  return '/api/v1';
+  if (typeof window !== 'undefined' && window.location?.hostname) {
+    return `${window.location.protocol}//${window.location.hostname}:8000/api/v1`;
+  }
+  return 'http://localhost:8000/api/v1';
 }
 
 const API_BASE = resolveApiBase();
@@ -54,6 +57,8 @@ let runtimeTokenResolver: ApiTokenResolver | null = null;
 
 type ApiRequestInit = Omit<RequestInit, 'headers'> & { headers?: HeadersInit };
 
+type ApiErrorPayload = { detail?: string } | null;
+
 /**
  * Normalizes candidate token values by trimming whitespace and filtering non-string values.
  */
@@ -163,6 +168,21 @@ function apiRequest(input: string, init: ApiRequestInit = {}): Promise<Response>
   });
 }
 
+/**
+ * Extracts backend error detail text from JSON payloads when available.
+ */
+async function responseErrorDetail(response: Response): Promise<string> {
+  try {
+    const payload = (await response.json()) as ApiErrorPayload;
+    if (payload && typeof payload.detail === 'string' && payload.detail.trim()) {
+      return payload.detail.trim();
+    }
+  } catch {
+    return '';
+  }
+  return '';
+}
+
 /**
  * Encodes query parameters while skipping undefined and null values.
  */
@@ -607,7 +627,8 @@ export async function updateAppSettings(payload: AppSettingsUpdate): Promise<App
     body: JSON.stringify(payload),
   });
   if (!response.ok) {
-    throw new Error('Failed to update settings');
+    const detail = await responseErrorDetail(response);
+    throw new Error(detail ? `Failed to update settings: ${detail}` : 'Failed to update settings');
   }
   return response.json() as Promise<AppSettings>;
 }

frontend/vite.config.ts

@@ -10,11 +10,5 @@ export default defineConfig({
   server: {
     host: '0.0.0.0',
     port: 5173,
-    proxy: {
-      '/api/v1': {
-        target: process.env.VITE_DEV_PROXY_TARGET ?? 'http://localhost:8000',
-        changeOrigin: true,
-      },
-    },
   },
 });