fix(request-body): 使用 deepcopy 防止请求体在处理流程中被意外修改

handler 基类和格式转换 registry 中，原始请求体通过浅拷贝或直接引用传递，
导致下游处理（模型映射、格式转换、重试整流）可能修改原始数据，
影响后续重试或并发请求的正确性。统一改用 copy.deepcopy 隔离副本。

tests/api/handlers/base/test_cli_request_body_isolation.py

@@ -0,0 +1,146 @@
+from __future__ import annotations
+
+import copy
+from types import SimpleNamespace
+from typing import Any
+
+import pytest
+
+import src.api.handlers.base.cli_stream_mixin as mixmod
+from src.api.handlers.base.cli_stream_mixin import CliStreamMixin
+from src.api.handlers.base.stream_context import StreamContext
+
+
+class _StopBuild(Exception):
+    pass
+
+
+class _DummyAuthInfo:
+    auth_header = "authorization"
+    auth_value = "Bearer test"
+    decrypted_auth_config = None
+
+    def as_tuple(self) -> tuple[str, str]:
+        return self.auth_header, self.auth_value
+
+
+class _CaptureBuilder:
+    def __init__(self) -> None:
+        self.request_body: dict[str, Any] | None = None
+
+    def build(self, request_body: dict[str, Any], *args: Any, **kwargs: Any) -> Any:
+        self.request_body = request_body
+        raise _StopBuild()
+
+
+class _DummyCliStreamHandler(CliStreamMixin):
+    FORMAT_ID = "openai:cli"
+
+    def __init__(self) -> None:
+        self.primary_api_format = "openai:cli"
+        self.request_id = "req-test"
+        self.api_key = SimpleNamespace(id="user-key-1")
+        self._request_builder = _CaptureBuilder()
+
+    async def _get_mapped_model(self, source_model: str, provider_id: str) -> str | None:
+        return None
+
+    def apply_mapped_model(self, request_body: dict[str, Any], mapped_model: str) -> dict[str, Any]:
+        out = dict(request_body)
+        out["model"] = mapped_model
+        return out
+
+    def prepare_provider_request_body(self, request_body: dict[str, Any]) -> dict[str, Any]:
+        request_body.pop("_aether_compact", None)
+        request_body["input"][0]["content"][0]["text"] = "prepared"
+        return request_body
+
+    def finalize_provider_request(
+        self,
+        request_body: dict[str, Any],
+        *,
+        mapped_model: str | None,
+        provider_api_format: str | None,
+    ) -> dict[str, Any]:
+        request_body["input"][0]["content"].append({"type": "input_text", "text": "finalized"})
+        return request_body
+
+    def get_model_for_url(
+        self,
+        request_body: dict[str, Any],
+        mapped_model: str | None,
+    ) -> str | None:
+        return mapped_model or str(request_body.get("model") or "")
+
+
+@pytest.mark.asyncio
+async def test_execute_stream_request_does_not_mutate_original_request_body(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    async def _fake_get_provider_auth(endpoint: Any, key: Any) -> _DummyAuthInfo:
+        return _DummyAuthInfo()
+
+    monkeypatch.setattr(mixmod, "get_provider_auth", _fake_get_provider_auth)
+    monkeypatch.setattr(
+        mixmod,
+        "get_provider_behavior",
+        lambda **kwargs: SimpleNamespace(
+            envelope=None,
+            same_format_variant=None,
+            cross_format_variant=None,
+        ),
+    )
+    monkeypatch.setattr(mixmod, "get_upstream_stream_policy", lambda *args, **kwargs: None)
+    monkeypatch.setattr(
+        mixmod,
+        "resolve_upstream_is_stream",
+        lambda *, client_is_stream, policy: client_is_stream,
+    )
+    monkeypatch.setattr(mixmod, "enforce_stream_mode_for_upstream", lambda *args, **kwargs: None)
+    monkeypatch.setattr(
+        mixmod,
+        "maybe_patch_request_with_prompt_cache_key",
+        lambda request_body, **kwargs: request_body,
+    )
+
+    handler = _DummyCliStreamHandler()
+    ctx = StreamContext(model="gpt-test", api_format="openai:cli")
+    ctx.client_api_format = "openai:cli"
+
+    provider = SimpleNamespace(name="provider", id="provider-1", provider_type="", proxy=None)
+    endpoint = SimpleNamespace(id="endpoint-1", api_format="openai:cli", base_url="https://x")
+    key = SimpleNamespace(id="key-1", proxy=None)
+    candidate = SimpleNamespace(
+        mapping_matched_model=None, needs_conversion=False, output_limit=None
+    )
+
+    original_request_body = {
+        "model": "gpt-test",
+        "_aether_compact": True,
+        "input": [
+            {
+                "role": "user",
+                "content": [
+                    {"type": "input_text", "text": "hello"},
+                ],
+            }
+        ],
+    }
+    snapshot = copy.deepcopy(original_request_body)
+
+    with pytest.raises(_StopBuild):
+        await handler._execute_stream_request(
+            ctx,
+            provider,
+            endpoint,
+            key,
+            original_request_body,
+            {},
+            candidate=candidate,
+        )
+
+    assert original_request_body == snapshot
+    assert handler._request_builder.request_body is not None
+    assert "_aether_compact" not in handler._request_builder.request_body
+    assert handler._request_builder.request_body["input"][0]["content"][0]["text"] == "prepared"
+    assert handler._request_builder.request_body["input"][0]["content"][-1]["text"] == "finalized"