diff --git a/s16_team_protocols/code.py b/s16_team_protocols/code.py
index d7993fb9e..104531625 100644
--- a/s16_team_protocols/code.py
+++ b/s16_team_protocols/code.py
@@ -547,22 +547,34 @@ def run():
                     inbox = BUS.read_inbox(name)
                     if not inbox:
                         continue
+                    should_resume = False
+                    idle_messages = []
                     for msg in inbox:
-                        if msg.get("type") in ("shutdown_request", "plan_approval_response"):
+                        msg_type = msg.get("type")
+                        if msg_type in ("shutdown_request", "plan_approval_response"):
                             should_stop = handle_inbox_message(name, msg, messages)
                             if should_stop:
                                 shutdown_requested = True
                                 break
+                            if msg_type == "plan_approval_response":
+                                should_resume = True
                         else:
-                            non_protocol.append(msg)
+                            idle_messages.append(msg)
                     if shutdown_requested:
                         break
-                    if non_protocol:
-                        inbox_json = json.dumps(non_protocol)
+                    if idle_messages:
+                        inbox_json = json.dumps(idle_messages)
                         messages.append({"role": "user",
                             "content": "<inbox>" + inbox_json + "</inbox>"})
+                        should_resume = True
+                    if should_resume:
                         break  # back to LLM turn with new messages
 
+                # A non-tool response has no tool calls to execute. Start a new
+                # LLM turn after inbox activity instead of appending an empty
+                # tool_result user message for the previous response.
+                continue
+
             # Execute tool calls
             results = []
             for block in response.content:
diff --git a/tests/test_s16_team_protocols.py b/tests/test_s16_team_protocols.py
new file mode 100644
index 000000000..fa1b36f87
--- /dev/null
+++ b/tests/test_s16_team_protocols.py
@@ -0,0 +1,138 @@
+from __future__ import annotations
+
+import importlib.util
+import os
+import sys
+import tempfile
+import threading
+import time
+import types
+from pathlib import Path
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+S16_PATH = REPO_ROOT / "s16_team_protocols" / "code.py"
+
+
+def load_s16(temp_cwd: Path):
+    fake_anthropic = types.ModuleType("anthropic")
+
+    class FakeAnthropic:
+        def __init__(self, *args, **kwargs):
+            self.messages = types.SimpleNamespace(create=None)
+
+    fake_dotenv = types.ModuleType("dotenv")
+    fake_anthropic.Anthropic = FakeAnthropic
+    fake_dotenv.load_dotenv = lambda override=True: None
+
+    previous_anthropic = sys.modules.get("anthropic")
+    previous_dotenv = sys.modules.get("dotenv")
+    previous_cwd = Path.cwd()
+    previous_model = os.environ.get("MODEL_ID")
+
+    spec = importlib.util.spec_from_file_location("s16_under_test", S16_PATH)
+    if spec is None or spec.loader is None:
+        raise RuntimeError(f"Unable to load {S16_PATH}")
+    module = importlib.util.module_from_spec(spec)
+
+    sys.modules["anthropic"] = fake_anthropic
+    sys.modules["dotenv"] = fake_dotenv
+    sys.modules[spec.name] = module
+    os.environ["MODEL_ID"] = "test-model"
+    try:
+        os.chdir(temp_cwd)
+        spec.loader.exec_module(module)
+        return module
+    finally:
+        os.chdir(previous_cwd)
+        if previous_anthropic is None:
+            sys.modules.pop("anthropic", None)
+        else:
+            sys.modules["anthropic"] = previous_anthropic
+        if previous_dotenv is None:
+            sys.modules.pop("dotenv", None)
+        else:
+            sys.modules["dotenv"] = previous_dotenv
+        if previous_model is None:
+            os.environ.pop("MODEL_ID", None)
+        else:
+            os.environ["MODEL_ID"] = previous_model
+
+
+def text_response(text: str):
+    return types.SimpleNamespace(
+        content=[types.SimpleNamespace(type="text", text=text)],
+        stop_reason="end_turn",
+    )
+
+
+def wait_until(predicate, timeout: float = 2.0) -> bool:
+    deadline = time.monotonic() + timeout
+    while time.monotonic() < deadline:
+        if predicate():
+            return True
+        time.sleep(0.01)
+    return predicate()
+
+
+def test_plan_approval_wakes_idle_teammate_without_empty_user_message():
+    with tempfile.TemporaryDirectory() as tmp:
+        module = load_s16(Path(tmp))
+        module.time = types.SimpleNamespace(
+            sleep=lambda _seconds: time.sleep(0.01),
+            time=time.time,
+        )
+
+        first_call = threading.Event()
+        second_call = threading.Event()
+        captured_messages = []
+
+        def create(**kwargs):
+            captured_messages.append(list(kwargs["messages"]))
+            if len(captured_messages) == 1:
+                first_call.set()
+                return text_response("Waiting for plan review.")
+            if len(captured_messages) == 2:
+                second_call.set()
+                return text_response("Approval received.")
+            raise AssertionError("unexpected extra LLM call")
+
+        module.client.messages.create = create
+        module.spawn_teammate_thread("bob", "developer", "Submit a plan.")
+
+        assert first_call.wait(1)
+        module.BUS.send(
+            "lead",
+            "bob",
+            "Approved",
+            "plan_approval_response",
+            {"request_id": "req_test", "approve": True},
+        )
+
+        assert second_call.wait(2), "plan approval should resume the idle teammate"
+        resumed_messages = captured_messages[1]
+        assert any(
+            message.get("role") == "user"
+            and message.get("content") == "[Plan approved] Proceed with the task."
+            for message in resumed_messages
+        )
+        assert not any(
+            message.get("role") == "user" and message.get("content") == []
+            for message in resumed_messages
+        )
+
+        module.BUS.send(
+            "lead",
+            "bob",
+            "Shut down",
+            "shutdown_request",
+            {"request_id": "req_shutdown"},
+        )
+        assert wait_until(lambda: "bob" not in module.active_teammates)
+
+        lead_messages = module.BUS.read_inbox("lead")
+        assert any(
+            message.get("type") == "shutdown_response"
+            and message.get("metadata", {}).get("request_id") == "req_shutdown"
+            for message in lead_messages
+        )