diff --git a/src/harness_sdk/instrumentation/grpc/__init__.py b/src/harness_sdk/instrumentation/grpc/__init__.py
index 728f8a3..bdb4d83 100644
--- a/src/harness_sdk/instrumentation/grpc/__init__.py
+++ b/src/harness_sdk/instrumentation/grpc/__init__.py
@@ -56,7 +56,8 @@ def server_wrapper(*args, **kwargs) -> None:
             logger.debug('Entering wrapper interceptors set')
             logger.debug(
                 'Setting server_interceptor_wrapper() as interceptor.')
-            kwargs["interceptors"] = [server_interceptor_wrapper(self)]
+            existing = list(kwargs.get("interceptors") or [])
+            kwargs["interceptors"] = [server_interceptor_wrapper(self)] + existing
             return self._original_wrapper_func(*args, **kwargs)
         grpc.server = server_wrapper
 
diff --git a/src/harness_sdk/instrumentation/requests/__init__.py b/src/harness_sdk/instrumentation/requests/__init__.py
index 7e265d8..7accd6f 100644
--- a/src/harness_sdk/instrumentation/requests/__init__.py
+++ b/src/harness_sdk/instrumentation/requests/__init__.py
@@ -2,6 +2,7 @@
 import logging
 from opentelemetry.instrumentation.requests import RequestsInstrumentor
 
+from harness_sdk.gen_ai.exceptions import ControlRequestBlocked
 from harness_sdk.plugins.control import get_control_registry
 from harness_sdk.instrumentation import BaseInstrumentorWrapper
 
@@ -28,7 +29,16 @@ def request_hook(self, span, request_obj):
         '''capture request data'''
         url = request_obj.url
         self.generic_request_handler(request_obj.headers, request_obj.body, span)
-        get_control_registry().evaluate(span, url, request_obj.headers, request_obj.body, False)
+        control_result = get_control_registry().evaluate(
+            span, url, request_obj.headers, request_obj.body, False
+        )
+        if control_result.block:
+            logger.debug(
+                "requests request blocked by control plugin: url=%s status=%s",
+                url,
+                control_result.response_status_code,
+            )
+            raise ControlRequestBlocked(control_result)
 
 
     def response_hook(self, span, _, response):
diff --git a/test/instrumentation/grpc/test_grpc_server_interceptors.py b/test/instrumentation/grpc/test_grpc_server_interceptors.py
new file mode 100644
index 0000000..38d0ba1
--- /dev/null
+++ b/test/instrumentation/grpc/test_grpc_server_interceptors.py
@@ -0,0 +1,30 @@
+"""grpc.server wrapper must preserve user-supplied interceptors."""
+from unittest.mock import MagicMock, patch
+
+import harness_sdk.instrumentation.grpc as grpc_module
+from harness_sdk.instrumentation.grpc import GrpcInstrumentorServerWrapper
+
+
+def test_server_wrapper_prepends_harness_interceptor():
+    wrapper = GrpcInstrumentorServerWrapper()
+    existing_interceptor = object()
+    original_server = MagicMock(return_value="server-instance")
+
+    with patch(
+        "harness_sdk.instrumentation.grpc.GrpcInstrumentorServer._instrument",
+        return_value=None,
+    ):
+        with patch(
+            "harness_sdk.instrumentation.grpc.server_interceptor_wrapper",
+            return_value="harness-interceptor",
+        ):
+            with patch("harness_sdk.instrumentation.grpc.grpc.server", original_server):
+                wrapper._instrument()  # pylint: disable=protected-access
+
+                grpc_module.grpc.server(
+                    futures=MagicMock(),
+                    interceptors=[existing_interceptor],
+                )
+
+    _, kwargs = original_server.call_args
+    assert kwargs["interceptors"] == ["harness-interceptor", existing_interceptor]
diff --git a/test/instrumentation/requests/test_requests_blocking.py b/test/instrumentation/requests/test_requests_blocking.py
new file mode 100644
index 0000000..cae45aa
--- /dev/null
+++ b/test/instrumentation/requests/test_requests_blocking.py
@@ -0,0 +1,60 @@
+"""Tests for requests client blocking via control plugins."""
+import pytest
+import requests
+
+from harness_sdk.gen_ai.exceptions import ControlRequestBlocked
+from harness_sdk.instrumentation.requests import RequestsInstrumentorWrapper
+from harness_sdk.plugins.control import ControlResult, get_control_registry
+from opentelemetry import trace
+from opentelemetry.sdk.trace import TracerProvider
+from opentelemetry.sdk.trace.export import SimpleSpanProcessor
+from opentelemetry.sdk.trace.export.in_memory_span_exporter import InMemorySpanExporter
+
+
+class _BlockingPlugin:
+    name = "test_blocking"
+    provides_blocking = True
+
+    def on_init(self, config):  # pylint: disable=unused-argument
+        pass
+
+    def evaluate(self, span, url, headers, body, is_grpc):  # pylint: disable=unused-argument
+        return ControlResult(
+            block=True,
+            response_status_code=403,
+            response_message="Blocked by policy",
+        )
+
+    def evaluate_agent_span(self, span, body=""):  # pylint: disable=unused-argument
+        return ControlResult()
+
+    def shutdown(self):
+        pass
+
+
+@pytest.fixture
+def requests_wrapper():
+    wrapper = RequestsInstrumentorWrapper()
+    yield wrapper
+    if wrapper.is_instrumented_by_opentelemetry:
+        wrapper.uninstrument()
+
+
+def test_requests_request_hook_raises_when_control_blocks(requests_wrapper):
+    exporter = InMemorySpanExporter()
+    provider = TracerProvider()
+    provider.add_span_processor(SimpleSpanProcessor(exporter))
+    trace.set_tracer_provider(provider)
+
+    get_control_registry().register(_BlockingPlugin())
+    requests_wrapper.instrument(tracer_provider=provider)
+
+    request_obj = requests.Request("GET", "https://example.com/get", headers={"x-test": "1"})
+    prepared = request_obj.prepare()
+    tracer = provider.get_tracer("test")
+    with tracer.start_as_current_span("requests") as span:
+        with pytest.raises(ControlRequestBlocked) as exc_info:
+            requests_wrapper.request_hook(span, prepared)
+
+    assert exc_info.value.result.response_status_code == 403
+    get_control_registry().clear()