diff --git a/agents/s13_background_tasks.py b/agents/s13_background_tasks.py
index ea19e6dc2..4fc0483d9 100644
--- a/agents/s13_background_tasks.py
+++ b/agents/s13_background_tasks.py
@@ -91,6 +91,7 @@ def __init__(self):
         self.tasks = {}  # task_id -> {status, result, command, started_at}
         self._notification_queue = []  # completed task results
         self._lock = threading.Lock()
+        self._condition = threading.Condition(self._lock)
 
     def _record_path(self, task_id: str) -> Path:
         return self.dir / f"{task_id}.json"
@@ -156,7 +157,7 @@ def _execute(self, task_id: str, command: str):
         self.tasks[task_id]["finished_at"] = time.time()
         self.tasks[task_id]["result_preview"] = preview
         self._persist_task(task_id)
-        with self._lock:
+        with self._condition:
             self._notification_queue.append({
                 "task_id": task_id,
                 "status": status,
@@ -164,6 +165,7 @@ def _execute(self, task_id: str, command: str):
                 "preview": preview,
                 "output_file": str(output_path.relative_to(WORKDIR)),
             })
+            self._condition.notify_all()
 
     def check(self, task_id: str = None) -> str:
         """Check status of one task or list all."""
@@ -189,7 +191,22 @@ def check(self, task_id: str = None) -> str:
 
     def drain_notifications(self) -> list:
         """Return and clear all pending completion notifications."""
-        with self._lock:
+        with self._condition:
+            notifs = list(self._notification_queue)
+            self._notification_queue.clear()
+        return notifs
+
+    def _has_running_tasks_locked(self) -> bool:
+        return any(task["status"] == "running" for task in self.tasks.values())
+
+    def has_running_tasks(self) -> bool:
+        with self._condition:
+            return self._has_running_tasks_locked()
+
+    def wait_for_notifications(self) -> list:
+        with self._condition:
+            while not self._notification_queue and self._has_running_tasks_locked():
+                self._condition.wait()
             notifs = list(self._notification_queue)
             self._notification_queue.clear()
         return notifs
@@ -286,24 +303,41 @@ def run_edit(path: str, old_text: str, new_text: str) -> str:
 ]
 
 
+def inject_background_results(messages: list, notifs: list) -> bool:
+    if notifs and messages:
+        lines = []
+        for notif in notifs:
+            suffix = ""
+            if notif.get("output_file"):
+                suffix = f" (output_file={notif['output_file']})"
+            lines.append(
+                f"[bg:{notif['task_id']}] {notif['status']}: "
+                f"{notif.get('preview') or '(no output)'}{suffix}"
+            )
+        notif_text = "\n".join(lines)
+        messages.append(
+            {
+                "role": "user",
+                "content": f"<background-results>\n{notif_text}\n</background-results>",
+            }
+        )
+        return True
+    return False
+
+
 def agent_loop(messages: list):
     while True:
-        # Drain background notifications and inject as a synthetic user/assistant
-        # transcript pair before the next model call (teaching demo behavior).
-        notifs = BG.drain_notifications()
-        if notifs and messages:
-            notif_text = "\n".join(
-                f"[bg:{n['task_id']}] {n['status']}: {n['preview']} "
-                f"(output_file={n['output_file']})"
-                for n in notifs
-            )
-            messages.append({"role": "user", "content": f"<background-results>\n{notif_text}\n</background-results>"})
+        inject_background_results(messages, BG.drain_notifications())
         response = client.messages.create(
             model=MODEL, system=SYSTEM, messages=messages,
             tools=TOOLS, max_tokens=8000,
         )
         messages.append({"role": "assistant", "content": response.content})
         if response.stop_reason != "tool_use":
+            if BG.has_running_tasks() and inject_background_results(
+                messages, BG.wait_for_notifications()
+            ):
+                continue
             return
         results = []
         for block in response.content:
diff --git a/agents/s_full.py b/agents/s_full.py
index 42eaddbbf..ada23a39e 100644
--- a/agents/s_full.py
+++ b/agents/s_full.py
@@ -742,6 +742,21 @@ def handle_plan_review(request_id: str, approve: bool, feedback: str = "") -> st
 ]
 
 
+def inject_background_results(messages: list, notifs: list) -> bool:
+    if notifs:
+        txt = "\n".join(
+            f"[bg:{n['task_id']}] {n['status']}: {n['result']}" for n in notifs
+        )
+        messages.append(
+            {
+                "role": "user",
+                "content": f"<background-results>\n{txt}\n</background-results>",
+            }
+        )
+        return True
+    return False
+
+
 # === SECTION: agent_loop ===
 def agent_loop(messages: list):
     rounds_without_todo = 0
@@ -752,11 +767,7 @@ def agent_loop(messages: list):
             print("[auto-compact triggered]")
             messages[:] = auto_compact(messages)
         # s08: drain background notifications
-        notifs = BG.drain()
-        if notifs:
-            txt = "\n".join(f"[bg:{n['task_id']}] {n['status']}: {n['result']}" for n in notifs)
-            messages.append({"role": "user", "content": f"<background-results>\n{txt}\n</background-results>"})
-            messages.append({"role": "assistant", "content": "Noted background results."})
+        inject_background_results(messages, BG.drain())
         # s10: check lead inbox
         inbox = BUS.read_inbox("lead")
         if inbox:
@@ -769,6 +780,10 @@ def agent_loop(messages: list):
         )
         messages.append({"role": "assistant", "content": response.content})
         if response.stop_reason != "tool_use":
+            if BG.has_running_tasks() and inject_background_results(
+                messages, BG.wait_for_notifications()
+            ):
+                continue
             return
         # Tool execution
         results = []
diff --git a/tests/test_background_notifications.py b/tests/test_background_notifications.py
new file mode 100644
index 000000000..b321c888c
--- /dev/null
+++ b/tests/test_background_notifications.py
@@ -0,0 +1,156 @@
+import os
+import sys
+import types
+import unittest
+from pathlib import Path
+from types import SimpleNamespace
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+if str(REPO_ROOT) not in sys.path:
+    sys.path.insert(0, str(REPO_ROOT))
+
+os.environ.setdefault("MODEL_ID", "test-model")
+
+fake_anthropic = types.ModuleType("anthropic")
+
+
+class FakeAnthropic:
+    def __init__(self, *args, **kwargs):
+        self.messages = SimpleNamespace(create=None)
+
+
+setattr(fake_anthropic, "Anthropic", FakeAnthropic)
+sys.modules.setdefault("anthropic", fake_anthropic)
+
+fake_dotenv = types.ModuleType("dotenv")
+setattr(fake_dotenv, "load_dotenv", lambda *args, **kwargs: None)
+sys.modules.setdefault("dotenv", fake_dotenv)
+
+import agents.s13_background_tasks as s13_background_tasks
+import agents.s_full as s_full
+
+
+class FakeMessagesAPI:
+    def __init__(self, responses):
+        self._responses = iter(responses)
+        self.call_count = 0
+
+    def create(self, **kwargs):
+        self.call_count += 1
+        return next(self._responses)
+
+
+class FakeS13BackgroundManager:
+    def __init__(self):
+        self._running = True
+        self.wait_called = False
+
+    def drain_notifications(self):
+        return []
+
+    def has_running_tasks(self):
+        return self._running
+
+    def wait_for_notifications(self):
+        self.wait_called = True
+        self._running = False
+        return [
+            {
+                "task_id": "bg-1",
+                "status": "completed",
+                "preview": "done",
+                "output_file": ".runtime-tasks/bg-1.log",
+            }
+        ]
+
+
+class FakeSFullBackgroundManager:
+    def __init__(self):
+        self._running = True
+        self.wait_called = False
+
+    def drain(self):
+        return []
+
+    def has_running_tasks(self):
+        return self._running
+
+    def wait_for_notifications(self):
+        self.wait_called = True
+        self._running = False
+        return [{"task_id": "bg-1", "status": "completed", "result": "done"}]
+
+
+class BackgroundNotificationTests(unittest.TestCase):
+    def test_s13_agent_loop_waits_for_background_results_after_end_turn(self):
+        messages = [{"role": "user", "content": "Run tests in the background"}]
+        fake_bg = FakeS13BackgroundManager()
+        fake_api = FakeMessagesAPI(
+            [
+                SimpleNamespace(
+                    stop_reason="end_turn", content="Started background work."
+                ),
+                SimpleNamespace(
+                    stop_reason="end_turn", content="Background work completed."
+                ),
+            ]
+        )
+        original_bg = s13_background_tasks.BG
+        original_client = s13_background_tasks.client
+        try:
+            s13_background_tasks.BG = fake_bg
+            s13_background_tasks.client = SimpleNamespace(messages=fake_api)
+            s13_background_tasks.agent_loop(messages)
+        finally:
+            s13_background_tasks.BG = original_bg
+            s13_background_tasks.client = original_client
+
+        self.assertTrue(fake_bg.wait_called)
+        self.assertEqual(fake_api.call_count, 2)
+        self.assertTrue(
+            any(
+                message["role"] == "user"
+                and isinstance(message["content"], str)
+                and "<background-results>" in message["content"]
+                for message in messages
+            )
+        )
+
+    def test_s_full_agent_loop_waits_for_background_results_after_end_turn(self):
+        messages = [{"role": "user", "content": "Run tests in the background"}]
+        fake_bg = FakeSFullBackgroundManager()
+        fake_api = FakeMessagesAPI(
+            [
+                SimpleNamespace(
+                    stop_reason="end_turn", content="Started background work."
+                ),
+                SimpleNamespace(
+                    stop_reason="end_turn", content="Background work completed."
+                ),
+            ]
+        )
+        original_bg = s_full.BG
+        original_client = s_full.client
+        try:
+            s_full.BG = fake_bg
+            s_full.client = SimpleNamespace(messages=fake_api)
+            s_full.agent_loop(messages)
+        finally:
+            s_full.BG = original_bg
+            s_full.client = original_client
+
+        self.assertTrue(fake_bg.wait_called)
+        self.assertEqual(fake_api.call_count, 2)
+        self.assertTrue(
+            any(
+                message["role"] == "user"
+                and isinstance(message["content"], str)
+                and "<background-results>" in message["content"]
+                for message in messages
+            )
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()