diff --git a/server/src/api/lifecycle.py b/server/src/api/lifecycle.py
index 49e91c077..d507cc9ac 100644
--- a/server/src/api/lifecycle.py
+++ b/server/src/api/lifecycle.py
@@ -429,11 +429,6 @@ async def proxy_sandbox_endpoint_request(request: Request, sandbox_id: str, port
 
     target_host = endpoint.endpoint
     query_string = request.url.query
-    target_url = (
-        f"http://{target_host}/{full_path}?{query_string}"
-        if query_string
-        else f"http://{target_host}/{full_path}"
-    )
 
     client: httpx.AsyncClient = request.app.state.http_client
 
@@ -463,9 +458,10 @@ async def proxy_sandbox_endpoint_request(request: Request, sandbox_id: str, port
 
         req = client.build_request(
             method=request.method,
-            url=target_url,
+            url=f"http://{target_host}/{full_path}",
+            params=query_string if query_string else None,
             headers=headers,
-            content=request.stream(),
+            content=request.stream() if request.method in ("POST", "PUT", "PATCH", "DELETE") else None,
         )
 
         resp = await client.send(req, stream=True)
diff --git a/server/tests/test_routes_proxy.py b/server/tests/test_routes_proxy.py
index 8bd042b03..cc6c183fb 100644
--- a/server/tests/test_routes_proxy.py
+++ b/server/tests/test_routes_proxy.py
@@ -39,10 +39,18 @@ def __init__(self):
         self.raise_connect_error = False
         self.raise_generic_error = False
 
-    def build_request(self, method: str, url: str, headers: dict, content):
+    def build_request(
+        self,
+        method: str,
+        url: str,
+        headers: dict,
+        content,
+        params: str | None = None,
+    ):
         self.built = {
             "method": method,
             "url": url,
+            "params": params,
             "headers": headers,
             "content": content,
         }
@@ -103,7 +111,8 @@ def get_endpoint(sandbox_id: str, port: int, resolve_internal: bool = False) ->
 
     assert fake_client.built is not None
     assert fake_client.built["method"] == "POST"
-    assert fake_client.built["url"] == "http://10.57.1.91:40109/api/run?q=search"
+    assert fake_client.built["url"] == "http://10.57.1.91:40109/api/run"
+    assert fake_client.built["params"] == "q=search"
     forwarded_headers = fake_client.built["headers"]
     lowered_headers = {k.lower(): v for k, v in forwarded_headers.items()}
     assert "host" not in lowered_headers
@@ -116,6 +125,87 @@ def get_endpoint(sandbox_id: str, port: int, resolve_internal: bool = False) ->
     assert lowered_headers.get("x-trace") == "trace-1"
 
 
+def test_proxy_forwards_get_request_with_query_params(
+    client: TestClient,
+    auth_headers: dict,
+    monkeypatch,
+) -> None:
+    """Test that GET requests with query parameters are forwarded correctly.
+
+    This test verifies the fix for issue #484 where GET requests with query
+    parameters were failing with 400 MISSING_QUERY when using use_server_proxy.
+    The query string should be passed via httpx params, not embedded in URL.
+    """
+    class StubService:
+        @staticmethod
+        def get_endpoint(sandbox_id: str, port: int, resolve_internal: bool = False) -> Endpoint:
+            assert sandbox_id == "sbx-123"
+            assert port == 44772
+            assert resolve_internal is True
+            return Endpoint(endpoint="10.57.1.91:40109")
+
+    monkeypatch.setattr(lifecycle, "sandbox_service", StubService())
+
+    fake_client = _FakeAsyncClient()
+    fake_client.response = _FakeStreamingResponse(
+        status_code=200,
+        headers={"content-type": "application/json"},
+        chunks=[b'[{"name":"file.txt","size":100}]'],
+    )
+    client.app.state.http_client = fake_client
+
+    response = client.get(
+        "/v1/sandboxes/sbx-123/proxy/44772/files/search",
+        params={"path": "/workspace"},
+        headers=auth_headers,
+    )
+
+    assert response.status_code == 200
+    assert fake_client.built is not None
+    assert fake_client.built["method"] == "GET"
+    assert fake_client.built["url"] == "http://10.57.1.91:40109/files/search"
+    assert fake_client.built["params"] == "path=%2Fworkspace"
+    assert fake_client.built["content"] is None
+
+
+def test_proxy_forwards_delete_request_with_body(
+    client: TestClient,
+    auth_headers: dict,
+    monkeypatch,
+) -> None:
+    """Test that DELETE requests with body payload are forwarded correctly.
+
+    This verifies that DELETE requests with JSON/body payload are not
+    incorrectly stripped when proxying.
+    """
+    class StubService:
+        @staticmethod
+        def get_endpoint(sandbox_id: str, port: int, resolve_internal: bool = False) -> Endpoint:
+            return Endpoint(endpoint="10.57.1.91:40109")
+
+    monkeypatch.setattr(lifecycle, "sandbox_service", StubService())
+
+    fake_client = _FakeAsyncClient()
+    fake_client.response = _FakeStreamingResponse(
+        status_code=200,
+        headers={"content-type": "application/json"},
+        chunks=[b'{"deleted":true}'],
+    )
+    client.app.state.http_client = fake_client
+
+    response = client.request(
+        "DELETE",
+        "/v1/sandboxes/sbx-123/proxy/44772/resources",
+        headers=auth_headers,
+        content=b'{"id": "resource-123"}',
+    )
+
+    assert response.status_code == 200
+    assert fake_client.built is not None
+    assert fake_client.built["method"] == "DELETE"
+    assert fake_client.built["content"] is not None
+
+
 def test_proxy_filters_response_hop_by_hop_headers(
     client: TestClient,
     auth_headers: dict,