diff --git a/strix/core/runner.py b/strix/core/runner.py
index ada35e79..f43b1d7f 100644
--- a/strix/core/runner.py
+++ b/strix/core/runner.py
@@ -592,16 +592,10 @@ async def run_strix_scan(
         )
         if not interactive and result is not None:
             final = getattr(result, "final_output", None)
-            scan_completed = False
-            if isinstance(final, str):
-                try:
-                    parsed = json.loads(final)
-                    scan_completed = bool(isinstance(parsed, dict) and parsed.get("scan_completed"))
-                except (ValueError, TypeError):
-                    scan_completed = False
-            elif isinstance(final, dict):
-                scan_completed = bool(final.get("scan_completed"))
-            if not scan_completed:
+            # Lifecycle tools mark the root completed. 
+            async with coordinator._lock:
+                root_completed = coordinator.statuses.get(root_id) == "completed"
+            if not root_completed:
                 logger.error(
                     "Scan %s ended without calling finish_scan. The agent "
                     "emitted a text-only turn instead of a lifecycle tool call, "
diff --git a/tests/test_runner_teardown.py b/tests/test_runner_teardown.py
index 4433c17d..d7e9645d 100644
--- a/tests/test_runner_teardown.py
+++ b/tests/test_runner_teardown.py
@@ -91,3 +91,31 @@ async def test_a_live_child_is_settled_before_sessions_close(
     task = child_task["t"]
     assert task.done(), "the child task was left running past scan teardown"
     assert task.cancelled(), "the child was not cancelled cleanly on a finish"
+
+
+@pytest.mark.parametrize(("root_status", "logged"), [("completed", False), ("stopped", True)])
+@pytest.mark.asyncio
+async def test_missing_finish_is_logged_only_when_root_did_not_complete(
+    monkeypatch: pytest.MonkeyPatch,
+    tmp_path: Any,
+    caplog: pytest.LogCaptureFixture,
+    root_status: str,
+    logged: bool,
+) -> None:
+    _wire_runner(monkeypatch, tmp_path)
+    coordinator = AgentCoordinator()
+
+    async def _root_ends_with_text(**kwargs: Any) -> Any:
+        await coordinator.set_status(kwargs["agent_id"], root_status)
+        return types.SimpleNamespace(final_output="The review is complete.")
+
+    monkeypatch.setattr(runner, "run_agent_loop", _root_ends_with_text)
+
+    await runner.run_strix_scan(
+        scan_config={"targets": [], "scan_mode": "deep"},
+        scan_id="scan-test",
+        image="img",
+        coordinator=coordinator,
+    )
+
+    assert ("ended without calling finish_scan" in caplog.text) is logged