diff --git a/adapters/llm.py b/adapters/llm.py
index a8f646d..8443301 100644
--- a/adapters/llm.py
+++ b/adapters/llm.py
@@ -274,6 +274,7 @@ class GovernedLLMClient:
         *,
         session_id: str | None = None,
         parent_call_id: str | None = None,
+        cache_salt: str | None = None,
     ) -> LLMResponse:
         """发起 LLM 调用，经四层治理栈：熔断 → 缓存 → 重试+流式 → 遥测。
 
@@ -281,6 +282,7 @@ class GovernedLLMClient:
             messages: OpenAI 格式消息列表。
             session_id: 会话 ID（传递到遥测）。
             parent_call_id: 父调用 ID（传递到遥测）。
+            cache_salt: 可选缓存盐，透传到 Redis 缓存键（如跨 epoch 重采样）。
 
         返回:
             LLMResponse 统一响应。
@@ -296,7 +298,11 @@ class GovernedLLMClient:
             raise CircuitOpenError(f"熔断器已开启，拒绝调用 provider={self._provider}")
 
         # ② 缓存查询（cache 为 None 时跳过）— call_id 在缓存路径独立生成
-        cached = await self._cache.get(self._model, messages) if self._cache is not None else None
+        cached = (
+            await self._cache.get(self._model, messages, cache_salt)
+            if self._cache is not None
+            else None
+        )
         if cached is not None:
             cache_call_id = str(uuid4())
             response = LLMResponse(
@@ -370,7 +376,7 @@ class GovernedLLMClient:
 
                 # ④ 写缓存（cache 为 None 时跳过）
                 if self._cache is not None:
-                    await self._cache.set(self._model, messages, response)
+                    await self._cache.set(self._model, messages, response, cache_salt)
 
                 # ⑤ 遥测
                 await self._telemetry.record_llm_call(
diff --git a/adapters/redis_cache.py b/adapters/redis_cache.py
index 4af573c..39420e6 100644
--- a/adapters/redis_cache.py
+++ b/adapters/redis_cache.py
@@ -29,36 +29,48 @@ class RedisResponseCache:
         self._redis = redis
         self._ttl_s = ttl_s
 
-    def _build_key(self, model: str, messages: list[dict[str, str]]) -> str:
+    def _build_key(
+        self,
+        model: str,
+        messages: list[dict[str, str]],
+        cache_salt: str | None = None,
+    ) -> str:
         """构造 content-addressed 缓存键。
 
         Args:
             model: 模型名称。
             messages: 消息列表。
+            cache_salt: 可选缓存盐（如跨 epoch 强制重采样）。仅当非 None 时才加入
+                键 payload，保证默认 None 时键结构与旧缓存一字节不差、旧键不失效。
 
         Returns:
             sha256 哈希字符串作为 Redis 键。
         """
-        payload = json.dumps(
-            {"model": model, "messages": messages},
-            sort_keys=True,
-            ensure_ascii=False,
-        )
+        key_obj: dict[str, Any] = {"model": model, "messages": messages}
+        if cache_salt is not None:
+            key_obj["salt"] = cache_salt
+        payload = json.dumps(key_obj, sort_keys=True, ensure_ascii=False)
         digest = hashlib.sha256(payload.encode("utf-8")).hexdigest()
         return f"llm_cache:{digest}"
 
-    async def get(self, model: str, messages: list[dict[str, str]]) -> LLMResponse | None:
+    async def get(
+        self,
+        model: str,
+        messages: list[dict[str, str]],
+        cache_salt: str | None = None,
+    ) -> LLMResponse | None:
         """从缓存读取 LLM 响应。
 
         Args:
             model: 模型名称。
             messages: 消息列表。
+            cache_salt: 可选缓存盐，透传到键构造。
 
         Returns:
             缓存命中时返回 LLMResponse，未命中或 Redis 异常时返回 None。
         """
         try:
-            key = self._build_key(model, messages)
+            key = self._build_key(model, messages, cache_salt)
             raw = await self._redis.get(key)
         except Exception:
             logger.warning("Redis 缓存读取失败，降级为未命中")
@@ -75,6 +87,7 @@ class RedisResponseCache:
         model: str,
         messages: list[dict[str, str]],
         response: LLMResponse,
+        cache_salt: str | None = None,
     ) -> None:
         """将 LLM 响应写入缓存。
 
@@ -82,9 +95,10 @@ class RedisResponseCache:
             model: 模型名称。
             messages: 消息列表。
             response: 待缓存的 LLMResponse。
+            cache_salt: 可选缓存盐，透传到键构造。
         """
         try:
-            key = self._build_key(model, messages)
+            key = self._build_key(model, messages, cache_salt)
             value = json.dumps(dataclasses.asdict(response), ensure_ascii=False)
             if self._ttl_s:
                 await self._redis.set(key, value, ex=self._ttl_s)
diff --git a/adapters/vlm.py b/adapters/vlm.py
index cf3342a..b959cb5 100644
--- a/adapters/vlm.py
+++ b/adapters/vlm.py
@@ -36,6 +36,7 @@ class GovernedVLMClient:
         *,
         session_id: str | None = None,
         parent_call_id: str | None = None,
+        cache_salt: str | None = None,
     ) -> LLMResponse:
         """图文调用：将图片编码为 base64 嵌入 messages，委托给 LLM 客户端。
 
@@ -45,6 +46,7 @@ class GovernedVLMClient:
             images: 图片文件路径列表。
             session_id: 会话 ID（遥测用）。
             parent_call_id: 父调用 ID（遥测用）。
+            cache_salt: 可选缓存盐，透传到底层 LLM 缓存键。
 
         返回:
             LLMResponse。
@@ -54,6 +56,7 @@ class GovernedVLMClient:
             vision_messages,
             session_id=session_id,
             parent_call_id=parent_call_id,
+            cache_salt=cache_salt,
         )
 
     @staticmethod
diff --git a/core/protocols.py b/core/protocols.py
index 3a08d27..2d4e89f 100644
--- a/core/protocols.py
+++ b/core/protocols.py
@@ -25,6 +25,7 @@ class LLMProvider(Protocol):
         *,
         session_id: str | None = None,
         parent_call_id: str | None = None,
+        cache_salt: str | None = None,
     ) -> LLMResponse: ...
 
 
@@ -39,6 +40,7 @@ class VLMProvider(Protocol):
         *,
         session_id: str | None = None,
         parent_call_id: str | None = None,
+        cache_salt: str | None = None,
     ) -> LLMResponse: ...
 
 
diff --git a/tests/unit/test_governed_llm.py b/tests/unit/test_governed_llm.py
index 923b6ec..9f487e4 100644
--- a/tests/unit/test_governed_llm.py
+++ b/tests/unit/test_governed_llm.py
@@ -23,8 +23,13 @@ class _FakeRedisCache:
     def __init__(self) -> None:
         self._store: dict[str, LLMResponse] = {}
 
-    async def get(self, model: str, messages: list[dict[str, str]]) -> LLMResponse | None:
-        key = f"{model}:{json.dumps(messages, sort_keys=True)}"
+    async def get(
+        self,
+        model: str,
+        messages: list[dict[str, str]],
+        cache_salt: str | None = None,
+    ) -> LLMResponse | None:
+        key = f"{model}:{cache_salt}:{json.dumps(messages, sort_keys=True)}"
         return self._store.get(key)
 
     async def set(
@@ -32,8 +37,9 @@ class _FakeRedisCache:
         model: str,
         messages: list[dict[str, str]],
         response: LLMResponse,
+        cache_salt: str | None = None,
     ) -> None:
-        key = f"{model}:{json.dumps(messages, sort_keys=True)}"
+        key = f"{model}:{cache_salt}:{json.dumps(messages, sort_keys=True)}"
         self._store[key] = response
 
 
diff --git a/tests/unit/test_redis_cache.py b/tests/unit/test_redis_cache.py
index 8523384..8b5945e 100644
--- a/tests/unit/test_redis_cache.py
+++ b/tests/unit/test_redis_cache.py
@@ -109,6 +109,18 @@ async def test_different_models_different_keys(
     assert await cache.get("claude-3-opus", MESSAGES) is None
 
 
+@pytest.mark.asyncio
+async def test_salt_changes_key(fake_redis: object) -> None:
+    """cache_salt 进入键：不同 salt 产生不同键，None 保持旧键结构。"""
+    cache = RedisResponseCache(redis=fake_redis, ttl_s=None)
+    k_none = cache._build_key("m", [{"role": "user", "content": "x"}], None)
+    k_e1 = cache._build_key("m", [{"role": "user", "content": "x"}], "run:e1")
+    k_e2 = cache._build_key("m", [{"role": "user", "content": "x"}], "run:e2")
+    assert k_none != k_e1
+    assert k_none != k_e2
+    assert k_e1 != k_e2
+
+
 @pytest.mark.asyncio
 async def test_graceful_degradation_on_error() -> None:
     """Redis 不可用时静默降级：get→None，set→不报错。"""