Add protected soft deletion for research runs

tests/test_rest_research.py

@@ -413,8 +413,8 @@ def test_get_report_not_completed(client: TestClient) -> None:
 # ---------------------------------------------------------------------------
 
 
-def test_delete_research_active_fails(client: TestClient) -> None:
-    """DELETE handles both active and finished research."""
+def test_delete_research_soft_deletes_all_states(client: TestClient) -> None:
+    """DELETE hides a run, including a completed one, instead of destroying it."""
     from nsct.api.rest_research import _research_store, ResearchRunState
 
     _research_store.clear()
@@ -434,14 +434,12 @@ def test_delete_research_active_fails(client: TestClient) -> None:
         # Already deleted by previous tests — skip
         return
 
-    # If completed, delete should return 400 (immutable)
-    # If failed/created, delete should succeed
     resp = client.delete(f"/v1/research/{research_id}")
-    assert resp.status_code in (200, 400)
-    if resp.status_code == 200:
-        body = resp.json()
-        assert body["status"] == "deleted"
-        assert body["research_id"] == research_id
+    assert resp.status_code == 200
+    body = resp.json()
+    assert body["status"] == "hidden"
+    assert body["research_id"] == research_id
+    assert research_id not in _research_store or _research_store[research_id].is_hidden
 
 
 def test_delete_research_not_found(client: TestClient) -> None: