refactor(compression): 请求压缩策略改为跟随客户端行为，响应支持gzip压缩

- 移除全局 ENABLE_REQUEST_COMPRESSION 配置，改为根据客户端 Content-Encoding
  决定是否对上游请求体进行 gzip 压缩
- 非流式响应根据客户端 Accept-Encoding 返回 gzip 压缩的 JSON
- ApiRequestContext 记录客户端编码偏好并透传至 handler 链路
- 新增 http_compression 模块统一处理压缩相关判断逻辑
- 上游请求头丢弃列表新增 content-encoding 防止客户端值泄露
- ensure_json_body 支持解压 gzip 编码的请求体

tests/unit/test_api_request_context.py

@@ -0,0 +1,91 @@
+from __future__ import annotations
+
+import gzip
+import json
+
+import pytest
+from fastapi import HTTPException
+from starlette.requests import Request
+
+from src.api.base.context import ApiRequestContext
+
+
+def _build_request(headers: dict[str, str] | None = None) -> Request:
+    header_items = [
+        (str(key).encode("latin-1"), str(value).encode("latin-1"))
+        for key, value in (headers or {}).items()
+    ]
+    scope = {
+        "type": "http",
+        "http_version": "1.1",
+        "method": "POST",
+        "scheme": "http",
+        "path": "/v1/messages",
+        "raw_path": b"/v1/messages",
+        "query_string": b"",
+        "headers": header_items,
+        "client": ("127.0.0.1", 12345),
+        "server": ("testserver", 80),
+    }
+
+    async def receive() -> dict[str, object]:
+        return {"type": "http.request", "body": b"", "more_body": False}
+
+    request = Request(scope, receive)
+    request.state.perf_metrics = {}
+    return request
+
+
+def _build_context(raw_body: bytes, headers: dict[str, str] | None = None) -> ApiRequestContext:
+    request = _build_request(headers=headers)
+    return ApiRequestContext(
+        request=request,
+        db=None,  # type: ignore[arg-type]
+        user=None,
+        api_key=None,
+        request_id="req_test",
+        start_time=0.0,
+        client_ip="127.0.0.1",
+        user_agent="pytest",
+        original_headers=headers or {},
+        query_params={},
+        raw_body=raw_body,
+    )
+
+
+class TestApiRequestContextEnsureJsonBody:
+    def test_decompresses_gzip_body(self) -> None:
+        payload = {"message": "hello", "count": 2}
+        raw_body = gzip.compress(json.dumps(payload).encode("utf-8"))
+        context = _build_context(raw_body, headers={"content-encoding": "gzip"})
+
+        result = context.ensure_json_body()
+
+        assert result == payload
+
+    def test_rejects_invalid_gzip_body(self) -> None:
+        context = _build_context(b"not-gzip-body", headers={"content-encoding": "gzip"})
+
+        with pytest.raises(HTTPException) as exc_info:
+            context.ensure_json_body()
+
+        assert exc_info.value.status_code == 400
+        assert exc_info.value.detail == "gzip 请求体解压失败"
+
+    def test_build_records_client_encoding_preferences(self) -> None:
+        request = _build_request(
+            headers={
+                "content-encoding": "gzip",
+                "accept-encoding": "gzip, deflate",
+            }
+        )
+        context = ApiRequestContext.build(
+            request=request,
+            db=None,  # type: ignore[arg-type]
+            user=None,
+            api_key=None,
+            raw_body=b"{}",
+        )
+
+        assert context.client_content_encoding == "gzip"
+        assert context.client_accept_encoding == "gzip, deflate"

tests/unit/test_headers.py

@@ -101,6 +101,7 @@ class TestBuildUpstreamHeaders:
                 "X-Api-Key": "client",
                 "User-Agent": "ua",
                 "Content-Type": "text/plain",
+                "Content-Encoding": "gzip",
             },
             "openai:chat",
             "provider",
@@ -112,6 +113,7 @@ class TestBuildUpstreamHeaders:
         assert result["Authorization"] == "Bearer provider"
         assert result["User-Agent"] == "extra"
         assert result["Content-Type"] == "text/plain"
+        assert "Content-Encoding" not in result
         assert result["X-Endpoint"] == "1"
         assert result["X-Extra"] == "1"
 

tests/unit/test_proxy_resolver_compression.py

@@ -0,0 +1,48 @@
+from __future__ import annotations
+
+import gzip
+import json
+
+from src.services.proxy_node.resolver import build_post_kwargs, build_stream_kwargs
+
+
+class TestProxyResolverCompression:
+    def test_build_post_kwargs_compresses_when_client_sent_gzip(self) -> None:
+        payload = {"message": "hello", "tokens": [1, 2, 3]}
+        kwargs = build_post_kwargs(
+            None,
+            url="https://example.com/v1/messages",
+            headers={"Content-Type": "application/json"},
+            payload=payload,
+            timeout=10.0,
+            client_content_encoding="gzip",
+        )
+
+        assert kwargs["headers"]["Content-Encoding"] == "gzip"
+        assert json.loads(gzip.decompress(kwargs["content"]).decode("utf-8")) == payload
+
+    def test_build_post_kwargs_keeps_plain_body_without_client_gzip(self) -> None:
+        payload = {"message": "plain"}
+        kwargs = build_post_kwargs(
+            None,
+            url="https://example.com/v1/messages",
+            headers={"Content-Type": "application/json"},
+            payload=payload,
+            timeout=10.0,
+            client_content_encoding=None,
+        )
+
+        assert "Content-Encoding" not in kwargs["headers"]
+        assert json.loads(kwargs["content"].decode("utf-8")) == payload
+
+    def test_build_stream_kwargs_drops_stale_content_encoding_header(self) -> None:
+        kwargs = build_stream_kwargs(
+            None,
+            url="https://example.com/v1/messages",
+            headers={"content-encoding": "gzip", "Content-Type": "application/json"},
+            payload={"message": "no-gzip"},
+            timeout=10.0,
+            client_content_encoding=None,
+        )
+
+        assert all(key.lower() != "content-encoding" for key in kwargs["headers"])