fix: normalise scope and blank strings on the construction path too

The verifier found four more env-only behaviours of the same class the branch
was already fixing. The worst is scope: it goes straight into the Redis keys
(pgw:limit:{scope}, pgw:gate:{scope}), so one process using from_env("LLM")
and another constructing scope="LLM" by hand split the rate limit and breaker
state across two namespaces, each tracking its own quota, with no error.

Blank redis_url and pricing_path now collapse to None as from_env has always
done, so they fall into the required-field checks instead of reaching the redis
client as an unparseable URL. EmbeddingSettings gains the __post_init__ it never
had, moving its batch_size and expected_dim checks off the from_env-only path.

Also adds the cache backend whitelist test that mutation testing showed missing.

tests/unit/test_config.py

@@ -7,7 +7,7 @@ import pytest
 from loguru import logger
 
 from polygateway.client import GatewayClient
-from polygateway.config import GatewaySettings, OcrSettings
+from polygateway.config import EmbeddingSettings, GatewaySettings, OcrSettings
 
 _BASE_ENV = {
     "LLM__QWEN__1__BASE_URL": "https://gw-a.example/v1",
@@ -271,6 +271,11 @@ class TestAssemblyGuards:
         with pytest.raises(ValueError, match="TELEMETRY_BACKEND"):
             GatewaySettings.from_env("LLM", env=_env(PGW_TELEMETRY_BACKEND="mysql"))
 
+    def test_cache_backend_whitelist(self):
+        """对称于上一条: env 层的域检查保留是为了报错能点出键名,得有测试守着。"""
+        with pytest.raises(ValueError, match="CACHE_BACKEND"):
+            GatewaySettings.from_env("LLM", env=_env(PGW_CACHE_BACKEND="rediss"))
+
     def test_pricing_path_optional(self):
         assert GatewaySettings.from_env("LLM", env=_env()).pricing_path is None
         s = GatewaySettings.from_env("LLM", env=_env(PGW_PRICING_PATH="conf/prices.json"))
@@ -552,6 +557,51 @@ class TestCrossFieldInvariants:
         assert settings.telemetry_pg_dsn == "postgresql://u@h/db"
         assert not warnings
 
+    # —— 构造期规范化: env 路一直在做的,构造路也要做(否则两条路产出不同的值)——
+
+    @pytest.mark.parametrize("raw", ["LLM", " llm ", " LLM "])
+    def test_scope_normalized_on_direct_construction(self, raw):
+        """scope 直接进 Redis key(pgw:limit:{scope}:…)。
+
+        大小写不一致会让同一逻辑 scope 的限流/熔断状态分裂到两套命名空间——
+        两边各记各的配额与熔断状态,分布式治理静默失效且不报错。
+        """
+        base = self._base()
+        assert dataclasses.replace(base, scope=raw).scope == "llm"
+
+    def test_blank_redis_url_normalized_to_none(self):
+        """空串此前只有 env 路归 None,构造路留着它骗过 `is None` 判断。"""
+        base = self._base()
+        assert dataclasses.replace(base, redis_url="").redis_url is None
+
+    def test_blank_redis_url_still_blocks_redis_backend(self):
+        """归 None 后必须落进条件必填,而不是放行到 redis 库去抛连接串天书。"""
+        base = self._base()
+        with pytest.raises(ValueError, match="redis_url"):
+            dataclasses.replace(base, limiter_backend="redis", redis_url="")
+
+    def test_blank_pricing_path_normalized_to_none(self):
+        base = self._base()
+        assert dataclasses.replace(base, pricing_path="").pricing_path is None
+
+    # —— EmbeddingSettings 自身的字段域(此前只有 from_env 校验)——
+
+    @pytest.mark.parametrize("bad", [0, -3])
+    def test_embedding_settings_rejects_non_positive_batch_size(self, bad):
+        base = self._base()
+        with pytest.raises(ValueError, match="batch_size"):
+            EmbeddingSettings(gateway=base, batch_size=bad)
+
+    def test_embedding_settings_rejects_non_positive_expected_dim(self):
+        base = self._base()
+        with pytest.raises(ValueError, match="expected_dim"):
+            EmbeddingSettings(gateway=base, batch_size=8, expected_dim=0)
+
+    def test_embedding_settings_accepts_valid_values(self):
+        base = self._base()
+        settings = EmbeddingSettings(gateway=base, batch_size=8, expected_dim=1024)
+        assert settings.batch_size == 8 and settings.expected_dim == 1024
+
     # —— 回归护栏: client.py 的 assert 前提确实被保证了 ——
 
     def test_factory_accepts_valid_redis_stack(self):