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.

tests/unit/test_thinking.py

@@ -6,11 +6,27 @@
 """
 
 import pytest
+from loguru import logger
 
-from polygateway.thinking import observe_thinking
+from polygateway.providers import get_provider
+from polygateway.thinking import (
+    DEFAULT_CAPABILITIES,
+    ThinkingCapability,
+    get_capability,
+    observe_thinking,
+    register_capability,
+    resolve_thinking,
+)
 from polygateway.types import ThinkingObservation
 
 
+def _warnings():
+    """捕获库发出的 WARNING;loguru 不经标准 logging,pytest 的 caplog 抓不到。"""
+    messages: list[str] = []
+    sink_id = logger.add(messages.append, level="WARNING")
+    return messages, sink_id
+
+
 class TestObserveThinking:
     """三态裁定: 证据硬度决定优先级,无信号一律 UNKNOWN。"""
 
@@ -74,3 +90,76 @@ def test_unknown_strings_are_rejected(bogus):
     """非法值必须抛 ValueError: 缓存回放靠它把污染数据挡成"未命中"(设计 §6)。"""
     with pytest.raises(ValueError):
         ThinkingObservation(bogus)
+
+
+class TestThinkingCapability:
+    """issue #5: 能力按 model 登记——同一 provider 内部代际差异是决定性的。"""
+
+    def test_registered_models_carry_evidence(self):
+        """登记必须附实测证据: 表会过期,没有出处就无从判断该不该信。"""
+        for model in ("MiniMax-M3", "MiniMax-M2.7", "MiniMax-M2.5"):
+            cap = get_capability(model)
+            assert cap is not None and cap.evidence.strip()
+
+    def test_m3_can_disable_but_m2x_cannot(self):
+        assert get_capability("MiniMax-M3").can_disable is True
+        assert get_capability("MiniMax-M2.7").can_disable is False
+        assert get_capability("MiniMax-M2.5").can_disable is False
+
+    def test_unregistered_model_is_unknown(self):
+        assert get_capability("some-brand-new-model") is None
+
+    def test_register_capability_is_pure(self):
+        table = register_capability("x-1", ThinkingCapability(True, "实测"))
+        assert get_capability("x-1", table=table) is not None
+        assert get_capability("x-1") is None  # 默认表未被污染
+
+    def test_default_capabilities_mapping_is_read_only(self):
+        with pytest.raises(TypeError):
+            DEFAULT_CAPABILITIES["hack"] = None  # type: ignore[index]
+
+
+class TestResolveThinking:
+    """五条判定规则(顺序即语义);设计 §5 真值表。"""
+
+    def test_rule1_none_injects_nothing(self):
+        got = resolve_thinking(get_provider("minimax"), None, None, model="MiniMax-M3")
+        assert got == {}
+
+    @pytest.mark.parametrize("enable", [True, False])
+    def test_rule2_unknown_shape_raises_and_points_the_way(self, enable):
+        with pytest.raises(ValueError, match="register_provider") as exc:
+            resolve_thinking(get_provider("openai"), None, enable, model="kimi-k3")
+        assert "extra_body" in str(exc.value)
+
+    def test_rule3_unregistered_model_warns_but_passes(self):
+        messages, sink_id = _warnings()
+        try:
+            got = resolve_thinking(get_provider("minimax"), None, False, model="MiniMax-M9")
+        finally:
+            logger.remove(sink_id)
+        assert got == {"reasoning_effort": "none"}
+        assert any("MiniMax-M9" in m for m in messages)
+
+    def test_rule4_cannot_disable_raises_with_the_model_name(self):
+        cap = get_capability("MiniMax-M2.7")
+        with pytest.raises(ValueError, match="MiniMax-M2.7"):
+            resolve_thinking(get_provider("minimax"), cap, False, model="MiniMax-M2.7")
+
+    def test_rule4_only_blocks_the_off_direction(self):
+        """关不掉 ≠ 开不了: M2.x 默认就在推理,开的方向不该被拦。"""
+        cap = get_capability("MiniMax-M2.7")
+        got = resolve_thinking(get_provider("minimax"), cap, True, model="MiniMax-M2.7")
+        assert got == {"reasoning_effort": "medium"}
+
+    def test_rule5_normal_path(self):
+        cap = get_capability("MiniMax-M3")
+        assert resolve_thinking(get_provider("minimax"), cap, False, model="MiniMax-M3") == {
+            "reasoning_effort": "none"
+        }
+
+    def test_unknown_shape_beats_capability_check(self):
+        """第 2 步先于第 4 步: 形态未知时无从注入,能力如何无关紧要。"""
+        cap = ThinkingCapability(can_disable=False, evidence="构造")
+        with pytest.raises(ValueError, match="register_provider"):
+            resolve_thinking(get_provider("openai"), cap, False, model="whatever")