diff --git a/navi/core/agent.py b/navi/core/agent.py
index 42f6168..7274e82 100644
--- a/navi/core/agent.py
+++ b/navi/core/agent.py
@@ -217,7 +217,12 @@
         if not note:
             return
         session.context.append(
-            Message(role="system", content=note, metadata={"source": "task_note"})
+            Message(
+                role="system",
+                content=note,
+                metadata={"source": "task_note"},
+                is_display=False,
+            )
         )
         await self._sessions.save(session)
         log.info("agent.task_notes_drained", session_id=session_id)
diff --git a/navi/core/context_builder.py b/navi/core/context_builder.py
index e3bb65f..cc8c50c 100644
--- a/navi/core/context_builder.py
+++ b/navi/core/context_builder.py
@@ -435,7 +435,14 @@
                 f"prefer this directory when no explicit working_dir is given."
             )
         system_msg = Message(role="system", content=system_prompt)
-        conv = [m for m in session_context if m.role != "system"]
+        # System-role history is normally infrastructure-only (hidden from the
+        # LLM), but background-task completion notes must stay visible — they
+        # are the agent's only guaranteed delivery of detached tool results.
+        conv = [
+            m for m in session_context
+            if m.role != "system"
+            or (m.metadata or {}).get("source") == "task_note"
+        ]
         conv = self._truncate_oversized(conv)
         result: list[Message] = [system_msg]
         if mem:
diff --git a/tests/unit/core/test_task_notes_injection.py b/tests/unit/core/test_task_notes_injection.py
index 8ab78e7..d5e36de 100644
--- a/tests/unit/core/test_task_notes_injection.py
+++ b/tests/unit/core/test_task_notes_injection.py
@@ -68,6 +68,28 @@
         # session was persisted
         assert agent._sessions.saved == [session]
 
+    async def test_note_survives_context_build_system_filter(self):
+        """Regression: build() used to drop ALL system-role history, so a
+        drained note was logged as delivered but never reached the LLM."""
+        from navi.core.context_builder import ContextBuilder
+        from tests.conftest_factory import make_profile, make_profile_registry
+
+        agent = make_agent_with_store()
+        session = make_session()
+        job = SimpleNamespace(
+            task_id="bt-ab12", session_id="s1", tool="terminal", status="completed",
+            subagent_tokens=None, preview=lambda limit=800: "BG-DONE-42",
+        )
+        await task_notes.add_note(job)
+        await agent._drain_task_notes("s1", session)
+
+        builder = ContextBuilder(profile_registry=make_profile_registry())
+        built = builder.build(session.context, make_profile("test"), None)
+
+        joined = "\n".join((m.content or "") for m in built)
+        assert "[Background task results]" in joined
+        assert "bt-ab12" in joined
+
     async def test_no_notes_nothing_injected(self):
         agent = make_agent_with_store()
         session = make_session()