DEVX-7: fix: make all warnings into errors across devx tools

tests/unit/test_distribute_molecule.py

@@ -240,6 +240,16 @@ class TestGithubEnv:
         assert result.exit_code != 0
 
 
+class TestRunnerIndexValidation:
+    def test_runner_index_zero_raises(self) -> None:
+        """Runner index < 1 should raise."""
+        with patch("devx.molecule.distribute_molecule.discover_scenarios", return_value=["dummy"]):
+            runner = CliRunner()
+            result = runner.invoke(cli, ["--runner-index", "0", "--max-runners", "3"])
+        assert result.exit_code != 0
+        assert "out of range" in result.output
+
+
 def test_main_module_block() -> None:
     import devx.molecule.distribute_molecule as dm