docs: retire the criterion this version disproved, everywhere it survived

The reasoning_tokens docstring was still teaching downstream to treat
None or 0 as no reasoning. The changelog and the schema page had both
been corrected; the docstring had not, and it is the copy that ships in
the wheel and shows up on hover. Someone writing a report from it would
have counted every real MiniMax reasoning call as not reasoning, which
is issue #16 all over again with the tests green.

The original wording stays, since reading pre-1.3.1 rows still needs
it. What follows it now says when it expired and what to read instead.

Two more places had drifted the same way: the changelog and the
architecture doc described the throttle and the cache fallback as they
were before this review, which is to say as the opposite of what the
code now does.

The claim that the two throttle sets would suppress each other does not
survive checking, as the mutation testing showed: their key spaces do
not overlap. Keeping them apart is still right, but for the honest
reason, which is that the two warnings have unrelated lifetimes.

src/polygateway/types.py

@@ -224,7 +224,12 @@ class LLMResponse:
     usage 时会用本地 tokenizer 补算并整体替换 usage 对象,把
     `completion_tokens_details` 一并吃掉(findings §4c 实测同一请求 10 轮呈
     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。"""
+    故下游判据须为 `in (None, 0)`,写 `== 0` 的条件永远不成立。
+
+    **该口径 2026-08-25 作废**(issue #16/#17): 供应商可能整体停报
+    `completion_tokens_details`(MiniMax 这一路实测已停),此时 `None` 只意味着
+    「没上报」而非「没推理」——同一次调用里库拿得到 185 字符推理正文。判「有没有
+    推理」一律改读 `thinking_observation`,上面那段只用于解读本版之前的历史数据。"""
 
     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)。