perf(api-server): normalize chat content linearly (#46079)

tests/gateway/test_api_server_normalize.py

@@ -1,5 +1,6 @@
 """Tests for _normalize_chat_content in the API server adapter."""
 
+from gateway.platforms import api_server
 from gateway.platforms.api_server import _normalize_chat_content
 
 
@@ -85,3 +86,19 @@ class TestNormalizeChatContent:
 
     def test_empty_list_returns_empty(self):
         assert _normalize_chat_content([]) == ""
+
+    def test_many_small_parts_normalize_without_quadratic_rescan(self, monkeypatch):
+        """Large content arrays should normalize in linear time."""
+        content = [{"type": "text", "text": "x"} for _ in range(1000)]
+        sum_calls = 0
+
+        def counting_sum(values):
+            nonlocal sum_calls
+            sum_calls += 1
+            return sum(values)
+
+        monkeypatch.setattr(api_server, "sum", counting_sum, raising=False)
+        result = _normalize_chat_content(content)
+
+        assert result.count("x") == 1000
+        assert sum_calls == 0