harden dashboard API contracts and proxy errors

apps/web/test_server.py

@@ -1,10 +1,14 @@
 import http.client
+import json
 import os
 import threading
 import unittest
 from unittest.mock import patch
 
 from server import ProxyStaticHandler
+from http.server import ThreadingHTTPServer
+
+RealHTTPConnection = http.client.HTTPConnection
 
 
 class FakeUpstream:
@@ -30,6 +34,22 @@ class ProxyServerTests(unittest.TestCase):
         with patch('server.http.client.HTTPConnection', FakeUpstream):
             self.assertTrue(server.proxy_api)
 
+    def test_upstream_failure_is_structured_json(self):
+        httpd = ThreadingHTTPServer(("127.0.0.1", 0), ProxyStaticHandler)
+        thread = threading.Thread(target=httpd.serve_forever, daemon=True)
+        thread.start()
+        try:
+            with patch('server.http.client.HTTPConnection', side_effect=OSError('connection refused')):
+                conn = RealHTTPConnection('127.0.0.1', httpd.server_port, timeout=3)
+                conn.request('GET', '/api/v1/dashboard/summary')
+                response = conn.getresponse()
+                body = response.read()
+            self.assertEqual(response.status, 502)
+            self.assertEqual(response.getheader('Content-Type'), 'application/json; charset=utf-8')
+            self.assertEqual(json.loads(body), {'error': 'api_upstream_unavailable'})
+        finally:
+            httpd.shutdown(); httpd.server_close(); thread.join(timeout=2)
+
 
 if __name__ == '__main__':
     unittest.main()