feat: add no-update sentinel handling to save_memory function and corresponding unit tests

surfsense_backend/app/services/memory/service.py

@@ -29,6 +29,15 @@ from app.services.memory.validation import (
 
 logger = logging.getLogger(__name__)
 
+_NO_UPDATE_SENTINELS = frozenset(
+    {
+        "NO_UPDATE",
+        "NO UPDATE",
+        "NO_CHANGE",
+        "NO CHANGE",
+    }
+)
+
 
 class MemoryScope(StrEnum):
     USER = "user"
@@ -149,6 +158,13 @@ async def save_memory(
     notice: str | None = None
     warnings: list[str] = []
 
+    if next_content.upper() in _NO_UPDATE_SENTINELS:
+        return SaveResult(
+            status="no_op",
+            message="No memory update requested.",
+            memory_md=old_memory,
+        )
+
     if len(next_content) > MEMORY_HARD_LIMIT and llm is not None:
         rewritten = await forced_rewrite(next_content, llm)
         if rewritten is not None and len(rewritten) < len(next_content):

surfsense_backend/tests/unit/services/test_memory_service.py

@@ -94,6 +94,54 @@ async def test_save_memory_rejects_long_no_heading_payload(monkeypatch) -> None:
     assert target.memory_md.startswith("## Facts")
 
 
+@pytest.mark.asyncio
+async def test_save_memory_no_update_sentinel_is_no_op(monkeypatch) -> None:
+    existing = "## Preferences\n- 2026-05-20: Existing preference\n"
+    target = SimpleNamespace(memory_md=existing)
+    session = _FakeSession()
+
+    async def fake_load_target(**_kwargs):
+        return target
+
+    monkeypatch.setattr("app.services.memory.service._load_target", fake_load_target)
+
+    result = await save_memory(
+        scope=MemoryScope.USER,
+        target_id="00000000-0000-0000-0000-000000000000",
+        content="NO_UPDATE",
+        session=session,
+    )
+
+    assert result.status == "no_op"
+    assert result.memory_md == existing
+    assert target.memory_md == existing
+    assert session.commit_calls == 0
+
+
+@pytest.mark.asyncio
+async def test_save_memory_no_update_sentinel_is_case_insensitive(monkeypatch) -> None:
+    existing = "## Preferences\n- 2026-05-20: Existing preference\n"
+    target = SimpleNamespace(memory_md=existing)
+    session = _FakeSession()
+
+    async def fake_load_target(**_kwargs):
+        return target
+
+    monkeypatch.setattr("app.services.memory.service._load_target", fake_load_target)
+
+    result = await save_memory(
+        scope=MemoryScope.USER,
+        target_id="00000000-0000-0000-0000-000000000000",
+        content="  no update  ",
+        session=session,
+    )
+
+    assert result.status == "no_op"
+    assert result.memory_md == existing
+    assert target.memory_md == existing
+    assert session.commit_calls == 0
+
+
 @pytest.mark.asyncio
 async def test_save_memory_grandfathers_existing_team_personal_heading(
     monkeypatch,