test: make the 429 red line actually catch its violation

Verifier mutation test: flipping _translate_429 to parse the summary
left all 824 tests green. The padding was one long string value, so the
cut landed inside it - and head-and-tail retention kept the trailing
error object, leaving the summary parseable. Many keys put the cut
between structural tokens, where the summary stops being valid JSON.
Mutation now fails as it should. Also splits OCR 429 out on its own.

tests/unit/test_openai_compat.py

@@ -16,6 +16,7 @@ from polygateway.errors import (
 )
 from polygateway.middleware.telemetry import TelemetryEmitter
 from polygateway.pricing import ModelPrice, PricingTable
+from polygateway.transports._http_errors import summarize_body
 from polygateway.transports.openai_compat import (
     OpenAICompatTransport,
     _iter_sse_deltas,
@@ -754,11 +755,20 @@ class TestErrorBodyRetention:
 
         摘要会破坏 JSON 结构,若改用摘要解析,超长 body 的配额耗尽将退化成普通
         限速——配额已耗尽的源不再 force_open,一个诊断改进就变成了治理 bug。
+
+        **填充必须是多个键**,不能是单个超长字符串值: 后者的截断点落在字符串
+        *内部*,省略标记成了合法的字符串内容,而头尾保留又让尾部的 error 对象
+        幸存——摘要照样解析得出 `insufficient_quota`,用例即告空转(2026-08-16
+        verifier 变异测试发现: 按错误写法实现,全套件 824 项依然全绿)。多键
+        填充让截断点落在结构记号之间,摘要才真正不可解析。
         """
         body = json.dumps(
-            {"padding": "P" * 4000, "error": {"type": "insufficient_quota", "message": "spent"}}
+            {**{f"k{i}": "v" * 10 for i in range(300)}, "error": {"type": "insufficient_quota"}}
         )
         assert len(body) > 2048
+        with pytest.raises(json.JSONDecodeError):
+            # 判别力的前提: 摘要确实不再是合法 JSON,读它必然拿不到 type
+            json.loads(summarize_body(body))
 
         def handler(request):
             return httpx.Response(429, content=body.encode())