diff --git a/mlpstorage_py/cli/help_formatter.py b/mlpstorage_py/cli/help_formatter.py
index 6f09fc40..9d5375b5 100644
--- a/mlpstorage_py/cli/help_formatter.py
+++ b/mlpstorage_py/cli/help_formatter.py
@@ -292,6 +292,7 @@
     --results-dir/-rd PATH
     [storage positional: file | object]
   Optional:
+    --checkpoint-subset             (8B at 8 processes only; declares a Subset run)
     --exec-type/-et {mpi,docker}    (default: mpi)
     --hosts/-s HOST...              (default: 127.0.0.1)
     --num-checkpoints-read/-ncr N   (default: 10; closed allows 10 or 0)
diff --git a/tests/unit/test_help_behavior.py b/tests/unit/test_help_behavior.py
index 557d6f86..0498dc43 100644
--- a/tests/unit/test_help_behavior.py
+++ b/tests/unit/test_help_behavior.py
@@ -49,6 +49,17 @@ def test_help_all_prints_synopsis(self, capsys):
         out = capsys.readouterr().out
         assert 'SYNOPSIS' in out
 
+    def test_help_all_documents_checkpoint_subset(self, capsys):
+        """--checkpoint-subset (added with the parser in 828cc63, storage#841)
+        must appear in the curated reference — the page is hand-maintained,
+        not generated from argparse, so a parser-only change silently omits
+        the flag here."""
+        with patch('sys.argv', ['mlpstorage', '--help_all']):
+            with pytest.raises(SystemExit):
+                parse_arguments()
+        out = capsys.readouterr().out
+        assert '--checkpoint-subset' in out
+
     def test_help_all_prints_kv_section(self, capsys):
         with patch('sys.argv', ['mlpstorage', '--help_all']):
             with pytest.raises(SystemExit):