diff --git a/src/polygateway/thinking.py b/src/polygateway/thinking.py
index da8af1f..55f3837 100644
--- a/src/polygateway/thinking.py
+++ b/src/polygateway/thinking.py
@@ -696,6 +696,13 @@ def _tier_unsupported(
         if fallback == "nearest" or effort is Effort.AUTO
         else ";若希望自动落到最近的档,请配 EFFORT_FALLBACK=nearest"
     )
+    if effort is Effort.AUTO:
+        example = capability.cheapest_effort or Effort.NONE
+        hint = (
+            ";请显式选择清单中的档位，例如 "
+            f"{{SCOPE}}__{{PROVIDER}}__{{N}}__REASONING_EFFORT={example.value}，"
+            f"或调用时传 reasoning_effort=Effort.{example.name}；库不会自动应用此选择"
+        )
     return f"{head}{body}{hint}"
 
 
diff --git a/tests/unit/test_client.py b/tests/unit/test_client.py
index af51c6b..e08e8b8 100644
--- a/tests/unit/test_client.py
+++ b/tests/unit/test_client.py
@@ -1316,3 +1316,27 @@ class TestManagedReasoningAdmission:
             assert (await client._limiter_backend.source_stats(source.name)).inflight == 0
         finally:
             await client._transport.aclose()
+
+
+async def test_managed_conflict_returns_half_open_probe_and_permit():
+    """本地拒绝没有上游响应，不计故障且必须归还半开探针。"""
+    from tests.contracts.conftest import FakeClock
+
+    clock = FakeClock()
+    source = _source(
+        provider="openai", reasoning_effort="high", extra_body={"reasoning_effort": "high"}
+    )
+    gate = InMemoryGate(config=BreakerConfig(1, 1, 10), now=clock)
+    entry = await gate.try_enter(source.name, "setup")
+    await gate.record_failure(entry, "source_dead", True)
+    clock.advance(2)
+    client = _client(sources=[source], breaker=gate)
+    try:
+        with pytest.raises(RequestRejectedError, match="冲突"):
+            await client.chat([])
+        assert (await client._limiter_backend.source_stats(source.name)).inflight == 0
+        next_entry = await gate.try_enter(source.name, "next")
+        assert next_entry.allowed and next_entry.is_probe
+        await gate.release_probe(next_entry)
+    finally:
+        await client._transport.aclose()
diff --git a/tests/unit/test_thinking.py b/tests/unit/test_thinking.py
index e3bb6bc..00c00cc 100644
--- a/tests/unit/test_thinking.py
+++ b/tests/unit/test_thinking.py
@@ -911,3 +911,14 @@ class TestThinkingRawOwnership:
         wire = ThinkingWire(off=None, on_base={"output_config": {"enabled": True}}, effort_key=None)
         with pytest.raises(ThinkingUnsupportedError):
             validate_thinking_raw(raw, effort=Effort.AUTO, wire=wire, origin="test")
+
+
+def test_auto_rejection_explains_how_to_choose_explicitly():
+    """可执行配置是指路，不由库自动应用其建议。"""
+    with pytest.raises(ThinkingUnsupportedError) as error:
+        resolve_thinking(
+            get_provider("minimax"), get_capability("MiniMax-M3"), Effort.AUTO, model="MiniMax-M3"
+        )
+    assert "REASONING_EFFORT=" in str(error.value)
+    assert "reasoning_effort=Effort." in str(error.value)
+    assert "EFFORT_FALLBACK=nearest" not in str(error.value)