fix: address completion verdict review findings

- fidelity cacheability also requires a non-empty projected body, so
  think-tag-only answers are no longer cached
- a no-argument tool sent with arguments null only is a deterministic
  dialect: ResultInvalid tool_arguments_null instead of retried
- text mode treats choice index null as 0 and no longer lets False pose
  as 0
- null-only tool_calls elements no longer produce an empty tool_calls
  list; non-stream fidelity checks role before the verdict; warning
  paths are length-bounded
- docs: ARCHITECTURE 7.8 field counts, README cache/watchdog wording,
  CHANGELOG notes, review record in the design, hook note in the plan

Red: 8 new tests failed before this change (e.g.
test_openai_cacheable_requires_projected_body,
test_null_arguments_tool_is_result_invalid_stream,
test_text_mode_choice_index_null_is_zero[None-True]).

tests/unit/test_cache.py

@@ -1116,3 +1116,14 @@ async def test_new_fields_roundtrip_through_cache():
     assert stored["finish_reason"] == "stop" and stored["stream_end"] == "eof_after_finish"
     hit = await mw(ChatRequest(messages=_MSGS), terminal)
     assert hit.cache_hit is True and hit.finish_reason == "stop" and hit.stream_end is None
+
+
+async def test_fidelity_think_only_projection_not_cached():
+    """审查 I1: qwen think 标签剥离后投影为空的保真结果不写缓存。"""
+    completion = OpenAIChatCompletion(
+        {"role": "assistant", "content": "<think>x</think>"}, "stop", "up", None
+    )
+    response = _resp(content="", thinking="x", finish_reason="stop", completion=completion)
+    backend = InMemoryCache()
+    await _mw(backend)(ChatRequest(messages=_MSGS, response_mode="openai"), _Terminal(response))
+    assert not backend._store

tests/unit/test_completion_transport.py

@@ -85,7 +85,7 @@ async def test_eof_after_finish_usage_only_frame_and_tools():
     result = await _run(frames, done=False, mode="openai")
     tool = result.completion.message["tool_calls"][0]
     assert tool["function"] == {"name": "lookup", "arguments": '{"q": 1}'}
-    assert result.stream_end == "eof_after_finish"
+    assert result.stream_end == "eof_after_finish" and result.usage_source == "measured"
 
 
 @pytest.mark.parametrize(
@@ -416,3 +416,38 @@ async def test_openai_reasoning_length_single_attempt_via_client():
         await client._transport.aclose()
     assert len(calls) == 1 and response.call_stats.attempts == 1
     assert response.stream_end == "eof_after_finish" and response.finish_reason == "length"
+
+
+async def test_eof_after_finish_stop_single_attempt_via_client():
+    """#31 验收 1 经治理链: stop + usage 无 DONE,attempts=1、不重试到耗尽。"""
+    from tests.unit.test_client import _client
+
+    calls = []
+
+    def handler(_):
+        calls.append(1)
+        return _sse_stream(_assistant(content="ok"), _f({}, "stop", _USAGE), done=False)
+
+    client = _client(handler=handler)
+    try:
+        response = await client.chat([{"role": "user", "content": "hi"}])
+    finally:
+        await client._transport.aclose()
+    assert len(calls) == 1 and response.call_stats.attempts == 1
+    assert response.stream_end == "eof_after_finish" and response.usage_source == "measured"
+
+
+async def test_text_salvage_with_length_partial_content_delivered():
+    """文本 salvage + length + 部分正文(finish 后无 usage): 交付、salvaged。"""
+    frames = [_assistant(content="part"), _f({}, finish="length")]
+    result = await _run(frames, done=False, missing_done="salvage")
+    assert result.content == "part" and result.stream_end == "salvaged"
+    assert result.finish_reason == "length"
+
+
+async def test_null_arguments_tool_is_result_invalid_stream():
+    """审查 I2: 无参函数 arguments 全程 null → ResultInvalid,不重试。"""
+    tool = {"index": 0, "id": "c", "type": "function", "function": {"name": "f", "arguments": None}}
+    frames = [_assistant(tool_calls=[tool]), _f({}, "tool_calls", _USAGE)]
+    with pytest.raises(ResultInvalidError, match="tool_arguments_null"):
+        await _run(frames, done=True, mode="openai")

tests/unit/test_completion_verdict.py

@@ -244,3 +244,22 @@ def test_stream_end_exported():
     import polygateway
 
     assert "StreamEnd" in polygateway.__all__
+
+
+def test_openai_cacheable_requires_projected_body():
+    """审查 I1: think 标签剥离后投影为空,即使原文非空也不可缓存。"""
+    think_only = _completion(content="<think>x</think>")
+    assert not _is_cacheable(
+        mode="openai", content="", finish_reason="stop", stream_end="done", completion=think_only
+    )
+
+
+def test_null_arguments_only_tool_is_result_invalid():
+    """审查 I2: 无参函数 arguments 全程 null(其余齐全)→ 确定性方言,ResultInvalid。"""
+    tool = {"id": "t1", "type": "function", "function": {"name": "f", "arguments": None}}
+    summary = _summarize_message({"role": "assistant", "tool_calls": [tool]}, "")
+    assert summary.null_arguments and not summary.tools_ok
+    verdict = _judge_outcome(mode="openai", summary=summary, finish="natural")
+    assert (verdict.error_kind, verdict.code) == ("result_invalid", "tool_arguments_null")
+    broken = {"id": "t1", "type": "function", "function": {"arguments": None}}
+    assert not _summarize_message({"role": "assistant", "tool_calls": [broken]}, "").null_arguments

tests/unit/test_openai_completion.py

@@ -421,3 +421,48 @@ def test_nonstream_null_tool_elements_stripped():
     assert parse_chat_completion(body).message["tool_calls"] == [tool]
     body["choices"][0]["message"]["tool_calls"] = None
     assert parse_chat_completion(body).message["tool_calls"] is None
+
+
+@pytest.mark.parametrize(("index", "taken"), [(None, True), (0, True), (False, False), (1, False)])
+def test_text_mode_choice_index_null_is_zero(index, taken):
+    """审查 I3: 文本模式 index:null 视缺省(=0);bool 不冒充 0。"""
+    state = ChatCompletionAccumulator(response_mode="text")
+    delta = state.add_chunk(
+        {"choices": [{"index": index, "delta": {"content": "hi"}, "finish_reason": "stop"}]}
+    )
+    assert (delta.content == "hi") is taken and (state.finish_reason == "stop") is taken
+
+
+def test_null_only_tool_elements_do_not_create_empty_list():
+    """审查 Minor1: tool_calls null 后 [null] 不得产出会被上游拒收的空数组。"""
+    state = ChatCompletionAccumulator(response_mode="openai")
+    _feed(
+        state,
+        _frame({"role": "assistant", "content": "a", "tool_calls": None}),
+        _frame({"tool_calls": [None]}, finish="stop"),
+    )
+    assert state.finish().message["tool_calls"] is None
+    body = {"choices": [{"message": {"role": "assistant", "content": "a", "tool_calls": [None]}}]}
+    assert parse_chat_completion(body).message["tool_calls"] is None
+
+
+def test_tool_calls_null_then_list_merges():
+    """tool_calls 先 null 后列表: 正常聚合工具。"""
+    state = ChatCompletionAccumulator(response_mode="openai")
+    tool = {"index": 0, "id": "a", "type": "function", "function": {"name": "f", "arguments": "{}"}}
+    _feed(
+        state,
+        _frame({"role": "assistant", "tool_calls": None}),
+        _frame({"tool_calls": [tool]}, finish="tool_calls"),
+    )
+    assert state.finish().message["tool_calls"][0]["id"] == "a"
+
+
+def test_nonstream_role_checked_before_verdict():
+    """审查 Minor3: 非流式缺 role 是形态失败,先于结局判定。"""
+    from polygateway.transports._openai_completion import check_completion_body
+
+    with pytest.raises(TransientError, match="role"):
+        check_completion_body(
+            {"choices": [{"message": {"content": "a"}, "finish_reason": "length"}]}
+        )