feat(adapters): 实现 RedisResponseCache

content-addressed sha256 缓存键，Redis 不可用时静默降级。

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/unit/test_redis_cache.py

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+"""RedisResponseCache 单元测试。"""
+
+from __future__ import annotations
+
+import pytest
+
+from adapters.redis_cache import RedisResponseCache
+from core.types import LLMResponse
+
+
+@pytest.fixture()
+def fake_redis():
+    """创建 fakeredis 异步实例。"""
+    try:
+        import fakeredis.aioredis
+    except ImportError:
+        pytest.skip("fakeredis not installed")
+    return fakeredis.aioredis.FakeRedis(decode_responses=True)
+
+
+@pytest.fixture()
+def sample_response() -> LLMResponse:
+    """构造一个标准测试用 LLMResponse。"""
+    return LLMResponse(
+        content="你好世界",
+        thinking="思考过程",
+        model="gpt-4o",
+        provider="openai",
+        prompt_tokens=10,
+        completion_tokens=5,
+        latency_ms=120,
+        ttft_ms=45.0,
+        max_inter_token_ms=12.3,
+        cache_hit=False,
+        call_id="test-call-001",
+    )
+
+
+MESSAGES = [{"role": "user", "content": "你好"}]
+
+
+class _BrokenRedis:
+    """模拟 Redis 连接异常的假实现。"""
+
+    async def get(self, _key: str) -> None:
+        raise ConnectionError("redis down")
+
+    async def set(self, _key: str, _value: str, **_kw: object) -> None:
+        raise ConnectionError("redis down")
+
+
+# ── 测试用例 ──────────────────────────────────────────────
+
+
+@pytest.mark.asyncio
+async def test_cache_miss_returns_none(fake_redis: object) -> None:
+    """缓存未命中时返回 None。"""
+    cache = RedisResponseCache(redis=fake_redis, ttl_s=60)
+    result = await cache.get("gpt-4o", MESSAGES)
+    assert result is None
+
+
+@pytest.mark.asyncio
+async def test_cache_roundtrip(
+    fake_redis: object, sample_response: LLMResponse
+) -> None:
+    """set 后 get 应返回相同内容。"""
+    cache = RedisResponseCache(redis=fake_redis, ttl_s=300)
+    await cache.set("gpt-4o", MESSAGES, sample_response)
+    result = await cache.get("gpt-4o", MESSAGES)
+
+    assert result is not None
+    assert result.content == sample_response.content
+    assert result.thinking == sample_response.thinking
+    assert result.model == sample_response.model
+    assert result.provider == sample_response.provider
+    assert result.prompt_tokens == sample_response.prompt_tokens
+    assert result.completion_tokens == sample_response.completion_tokens
+    assert result.latency_ms == sample_response.latency_ms
+    assert result.ttft_ms == sample_response.ttft_ms
+    assert result.max_inter_token_ms == sample_response.max_inter_token_ms
+    assert result.cache_hit == sample_response.cache_hit
+    assert result.call_id == sample_response.call_id
+
+
+@pytest.mark.asyncio
+async def test_different_messages_different_keys(
+    fake_redis: object, sample_response: LLMResponse
+) -> None:
+    """不同 messages 应产生不同缓存键。"""
+    cache = RedisResponseCache(redis=fake_redis, ttl_s=300)
+    messages_a = [{"role": "user", "content": "问题A"}]
+    messages_b = [{"role": "user", "content": "问题B"}]
+
+    await cache.set("gpt-4o", messages_a, sample_response)
+
+    assert await cache.get("gpt-4o", messages_a) is not None
+    assert await cache.get("gpt-4o", messages_b) is None
+
+
+@pytest.mark.asyncio
+async def test_different_models_different_keys(
+    fake_redis: object, sample_response: LLMResponse
+) -> None:
+    """不同 model 应产生不同缓存键。"""
+    cache = RedisResponseCache(redis=fake_redis, ttl_s=300)
+
+    await cache.set("gpt-4o", MESSAGES, sample_response)
+
+    assert await cache.get("gpt-4o", MESSAGES) is not None
+    assert await cache.get("claude-3-opus", MESSAGES) is None
+
+
+@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。"""
+    cache = RedisResponseCache(redis=_BrokenRedis(), ttl_s=60)
+    response = LLMResponse(
+        content="x",
+        thinking="",
+        model="m",
+        provider="p",
+        prompt_tokens=0,
+        completion_tokens=0,
+        latency_ms=0,
+        ttft_ms=None,
+        max_inter_token_ms=None,
+        cache_hit=False,
+        call_id="broken-test",
+    )
+
+    # get 应返回 None 而非抛异常
+    assert await cache.get("m", MESSAGES) is None
+
+    # set 应静默吞掉异常
+    await cache.set("m", MESSAGES, response)