feat: carry the reasoning verdict through to LLMResponse

Both assembly paths fill it, streaming and non-streaming alike. Filling
only one is exactly the divergence this issue exposed: M3 returns
reasoning prose over SSE and nothing at all over the plain endpoint, so
a verdict computed on one path says nothing about the other.

The field defaults to UNKNOWN on both TransportResult and LLMResponse.
A transport that does not judge should not get to declare absence on
the provider's behalf, and a default that stays silent is the only one
that cannot lie.

src/polygateway/types.py

@@ -226,6 +226,15 @@ class LLMResponse:
     6:4 双峰)。实测三家供应商在未推理时都是整个 details 缺失、无人上报 `0`,
     故下游判据须为 `in (None, 0)`,写 `== 0` 的条件永远不成立。"""
 
+    thinking_observation: ThinkingObservation = ThinkingObservation.UNKNOWN
+    """本次调用"推理是否真的发生"的三态裁定(issue #16/#17)。
+
+    `UNKNOWN` = **本次无任何信号,判不出来**,**不是**"没推理"——把两者折叠
+    是 `reasoning_tokens=None` 制造的老歧义。典型来源: 非流式路径下部分模型
+    推理已计费却既不回传正文也不回传 `completion_tokens_details`(MiniMax-M3
+    实测开启档 completion 53 vs 关闭档 3),该档即为 `UNKNOWN`。
+    要判"确实没推理"只认 `ABSENT`(上游明确上报 0)。"""
+
 
 @dataclass(frozen=True)
 class ChatRequest:
@@ -321,6 +330,11 @@ class TransportResult:
     cached_prompt_tokens: int | None = None
     model_reported: str | None = None
     reasoning_tokens: int | None = None
+    thinking_observation: ThinkingObservation = ThinkingObservation.UNKNOWN
+    """本次调用"推理是否真的发生"的裁定(issue #16/#17),由 transport 组装时填。
+
+    默认 `UNKNOWN` 而非 `ABSENT`: 不做裁定的 transport(OCR/embedding 等)沉默
+    时,不该替上游做出"没推理"这个它从未做过的声明。"""
 
 
 @dataclass(frozen=True)