refactor: give reasoning decisions their own module

providers.py had been holding two jobs: the registry of what each
provider looks like, and the decisions made from those declarations.
Adding response-side judgement would have made it the module for
everything about reasoning, so the decisions move to thinking.py and
the registry keeps only profiles and their lookup.

Moving a module breaks any deep-path import of what moved, so the six
public symbols are promoted to the package root at the same time. The
top level is this library's stated API surface; giving downstream a
stable name to import is what makes the next reorganisation harmless.
observe_thinking stays unexported — downstream reads the verdict off
LLMResponse, and exporting it would be a permanent promise for nothing.

src/polygateway/thinking.py

@@ -7,6 +7,14 @@
 内层 `types.py`;定义在这里会让 `types.py` 反向 import 决策模块(依赖铁律)。
 """
 
+from collections.abc import Mapping
+from dataclasses import dataclass
+from types import MappingProxyType
+from typing import Any
+
+from loguru import logger
+
+from polygateway.providers import ProviderProfile
 from polygateway.types import ThinkingObservation
 
 
@@ -27,3 +35,141 @@ def observe_thinking(*, thinking: str, reasoning_tokens: int | None) -> Thinking
     if reasoning_tokens is None:
         return ThinkingObservation.UNKNOWN
     return ThinkingObservation.OBSERVED if reasoning_tokens > 0 else ThinkingObservation.ABSENT
+
+
+class ThinkingUnsupportedError(ValueError):
+    """推理开关无法满足: 形态未知或该模型不支持该方向(issue #5)。
+
+    是 `ValueError` 的子类而非 `errors.py` 四分类之一——它描述的是**配置**
+    不可满足(装配期就该炸),不是一次调用的运行时失败。transport 在请求期
+    捕获它并翻译为 `RequestRejectedError` 再进四分类。单列一个类型是为了让
+    捕获点能精确到它,而不是宽catch 整个 `ValueError`(那会把序列化等无关
+    错误误贴成"推理开关无法满足")。
+    """
+
+
+@dataclass(frozen=True)
+class ThinkingCapability:
+    """某个**具体模型**能否关闭推理(issue #5);登记必须附实测证据与日期。
+
+    与 `ProviderProfile` 的分工: 后者声明**形态**(参数长什么样,按 provider 变,
+    数年不变一次),本类声明**能力**(按 model 变,同一 provider 每代都变)。二者
+    合一在 provider 级表达不了代际差异——实测 MiniMax-M3 可关闭推理,而同厂的
+    M2.7/M2.5 三种参数形态全部无效(findings §2.3),profile 一格管不住三个模型。
+
+    `evidence` 不是装饰: 能力表过期是必然事件,没有出处就无从判断该不该信它。
+    """
+
+    can_disable: bool
+    evidence: str
+
+
+DEFAULT_CAPABILITIES: Mapping[str, ThinkingCapability] = MappingProxyType(
+    {
+        "MiniMax-M3": ThinkingCapability(
+            can_disable=True,
+            evidence="2026-08-02 经 new-api 中转实测 N=10: reasoning_effort=none 稳定关闭,零跳变",
+        ),
+        "MiniMax-M2.7": ThinkingCapability(
+            can_disable=False,
+            evidence=(
+                "2026-08-02 实测 reasoning_effort=none / thinking:{disabled} / thinking:{adaptive} "
+                "各 N=3 全部无效;OpenRouter 注册表登记 mandatory:true,models.dev 登记无控制手段"
+            ),
+        ),
+        "MiniMax-M2.5": ThinkingCapability(
+            can_disable=False,
+            evidence="2026-08-02 实测同 M2.7: 三种形态各 N=3 全部无效;外部注册表同样登记为强制推理",
+        ),
+        "qwen3.7-plus": ThinkingCapability(
+            can_disable=True,
+            evidence="2026-08-02 实测 enable_thinking=false 关闭(completion 5 token,无推理)",
+        ),
+        "deepseek-v4-pro": ThinkingCapability(
+            can_disable=True,
+            evidence="2026-08-02 实测 thinking:{type:disabled} 关闭(completion 3 token,无推理)",
+        ),
+    }
+)
+"""在用模型的推理能力登记(YAGNI: 不覆盖全世界,未登记走 `resolve_thinking` 退化)。"""
+
+
+def get_capability(
+    model: str, *, table: Mapping[str, ThinkingCapability] | None = None
+) -> ThinkingCapability | None:
+    """按模型名精确查找;未登记返回 None(= 能力未知,由调用方决定如何退化)。
+
+    与 `get_provider` 未注册即报错不同: provider 是配置里写死的少数几个值,
+    写错就是配置错误;而模型名千变万化,新模型上线不该被库挡住(设计 §5 R4)。
+    """
+    return (DEFAULT_CAPABILITIES if table is None else table).get(model)
+
+
+def register_capability(
+    model: str,
+    capability: ThinkingCapability,
+    *,
+    base: Mapping[str, ThinkingCapability] | None = None,
+) -> dict[str, ThinkingCapability]:
+    """纯函数注册: 返回 base(缺省 DEFAULT_CAPABILITIES)+ 新条目的新表,同名覆盖。"""
+    table = dict(DEFAULT_CAPABILITIES if base is None else base)
+    table[model] = capability
+    return table
+
+
+def resolve_thinking(
+    profile: ProviderProfile,
+    capability: ThinkingCapability | None,
+    enable_thinking: bool | None,
+    *,
+    model: str,
+    warn_unregistered: bool = True,
+) -> Mapping[str, Any]:
+    """三态 + 两层能力 → 请求体注入片段;不可满足时 ValueError。
+
+    调用点负责翻译: 装配期直接冒泡(配置错误),transport 内翻译为
+    `RequestRejectedError`(四分类之一)。判定顺序即语义,不可调换——形态未知时
+    无从注入,能力如何无关紧要,故 Phase 2 必须先于 Phase 4;未登记模型没有
+    `can_disable` 可读,故 Phase 3 必须先于 Phase 4。
+
+    `model` 只用于错误与告警文案: 报错能定位到具体模型才有可操作性,而
+    `capability` 为 None(未登记)时无从从别处取得模型名。
+
+    `warn_unregistered=False` 供请求热路径去重用: 装配期已经喊过一次,逐次
+    调用再喊只会刷屏。判定结果不受此参数影响。
+    """
+    # Phase 1: 调用方不表态 —— 与 False 严格区分,用模型默认档
+    if enable_thinking is None:
+        return {}
+    slot = profile.thinking_on if enable_thinking else profile.thinking_off
+    direction = "thinking_on" if enable_thinking else "thinking_off"
+    # Phase 2: 形态未知 —— 提供了开关却不知道怎么发,静默放行就是欺骗调用方
+    if slot is None:
+        raise ThinkingUnsupportedError(
+            f"provider {profile.name!r} 的 {direction} 形态未知(模型 {model!r}): "
+            f"本库不知道该 provider 如何表达这一档。请用 register_provider 注册形态,"
+            f"或改用 SourceConfig.extra_body 直接下发供应商参数"
+        )
+    # Phase 3: 能力未登记 —— 新模型上线不该被库挡住,但也不该假装成功
+    if capability is None:
+        if warn_unregistered:
+            _warn_unregistered(model, profile, slot)
+        return slot
+    # Phase 4: 明确不支持关闭 —— 调用方要的是"不推理"的语义保证,给不了必须说
+    if enable_thinking is False and not capability.can_disable:
+        raise ThinkingUnsupportedError(
+            f"模型 {model!r} 无法关闭推理,enable_thinking=False 无法满足: "
+            f"{capability.evidence}。该模型的推理是固有属性,任何参数都关不掉——"
+            f"需要关闭思维链请换用支持关闭的模型"
+        )
+    return slot
+
+
+def _warn_unregistered(model: str, profile: ProviderProfile, slot: Mapping[str, Any]) -> None:
+    logger.warning(
+        "模型 {} 的推理能力未登记,按 provider {} 的形态尽力注入 {};"
+        "若该模型实际不支持这一档,本次设置将静默失效。实测后请用 register_capability 登记",
+        model,
+        profile.name,
+        dict(slot),
+    )