feat: model the thinking switch as shape plus capability (issue #5)

enable_thinking=False was a no-op for minimax and openai sources: both
profiles had empty dicts on each side, so the payload update injected
nothing while the caller believed reasoning had been turned off. A
downstream project was blocked on exactly this.

The root cause is that an empty dict meant two different things -- "no
injection needed" and "we do not know how this provider spells it" --
and that a provider-level table cannot express what turned out to be a
per-model property. Live testing showed MiniMax-M3 can disable
reasoning via reasoning_effort while M2.7 and M2.5 cannot be disabled
at all, which two external registries independently confirm.

So the shape stays at provider level and a capability table joins it at
model level. Unknown, unsupported and no-opinion are now three distinct
values, and resolve_thinking is the single place they meet: it raises at
assembly time when a model cannot honour the request, warns and injects
for unregistered models, and injects silently otherwise. Every registered
capability carries the evidence it was derived from.

enable_thinking also joins the cache fingerprint, since it now really
does change the request body.

tests/unit/test_openai_compat.py

@@ -506,6 +506,65 @@ class TestRequestShaping:
             assert "enable_thinking" not in seen
         assert seen["stream_options"] == {"include_usage": True}
 
+    @pytest.mark.parametrize(
+        ("enable_thinking", "expected"),
+        [(True, "medium"), (False, "none")],
+    )
+    async def test_minimax_injects_reasoning_effort(self, enable_thinking, expected):
+        """issue #5: MiniMax 认的是 reasoning_effort,不是 enable_thinking。"""
+        seen = {}
+
+        def handler(request):
+            seen.update(json.loads(request.content))
+            return _sse_stream(_chunk(content="x"), _chunk(usage=_USAGE))
+
+        source = _source(
+            name="mm", provider="minimax", model="MiniMax-M3", enable_thinking=enable_thinking
+        )
+        await _complete(_transport_for(handler), source)
+        assert seen["reasoning_effort"] == expected
+        assert "enable_thinking" not in seen  # 旧形态实测被静默丢弃,不再下发
+
+    async def test_extra_body_overrides_the_profile_slot(self):
+        """注入顺序即优先级: profile → extra_body → overlay,两行不可调换。"""
+        seen = {}
+
+        def handler(request):
+            seen.update(json.loads(request.content))
+            return _sse_stream(_chunk(content="x"), _chunk(usage=_USAGE))
+
+        source = _source(
+            name="mm",
+            provider="minimax",
+            model="MiniMax-M3",
+            enable_thinking=True,
+            extra_body={"reasoning_effort": "high"},
+        )
+        await _complete(_transport_for(handler), source)
+        assert seen["reasoning_effort"] == "high"
+
+    async def test_model_that_cannot_disable_is_rejected_not_silently_ignored(self):
+        """M2.x 关不掉推理: 必须是四分类之一的 RequestRejected,不是裸 ValueError。
+
+        裸异常会逃出 chat() —— 它不属错误四分类、TelemetryMW 也不捕,结果是一行
+        遥测都没有就崩了(设计 §5.1)。
+        """
+
+        def handler(request):  # pragma: no cover - 不该走到发请求
+            raise AssertionError("请求不该发出")
+
+        source = _source(name="mm", provider="minimax", model="MiniMax-M2.7", enable_thinking=False)
+        with pytest.raises(RequestRejectedError, match="MiniMax-M2.7"):
+            await _complete(_transport_for(handler), source)
+
+    async def test_unknown_shape_is_rejected(self):
+        def handler(request):  # pragma: no cover - 不该走到发请求
+            raise AssertionError("请求不该发出")
+
+        source = _source(name="k3", provider="openai", model="kimi-k3", enable_thinking=False)
+        with pytest.raises(RequestRejectedError, match="register_provider"):
+            await _complete(_transport_for(handler), source)
+
     async def test_overlay_merged_into_payload(self):
         seen = {}