fix(probes): guard badchars ASCII selection against max_ascii_variants=1

garak/probes/badchars.py

@@ -383,6 +383,10 @@ def _select_positions(
     def _select_ascii(limit: int) -> List[str]:
         if limit is None or limit <= 0 or limit >= len(ASCII_PRINTABLE):
             return list(ASCII_PRINTABLE)
+
+        if limit == 1:
+            return [ASCII_PRINTABLE[0]]
+
         step = max(1, (len(ASCII_PRINTABLE) - 1) // (limit - 1))
         selected = [ASCII_PRINTABLE[i] for i in range(0, len(ASCII_PRINTABLE), step)]
         return selected[:limit]

tests/probes/test_probes_badchars.py

@@ -0,0 +1,21 @@
+"""Regression tests for the badchars probe ASCII variant cap."""
+
+import pytest
+
+from garak.probes.badchars import ASCII_PRINTABLE, BadCharacters
+
+
+@pytest.mark.parametrize(
+    ("limit", "expected_count"),
+    [
+        (1, 1),
+        (2, 2),
+        (3, 3),
+    ],
+)
+def test_select_ascii_respects_small_limits(limit: int, expected_count: int) -> None:
+    selected = BadCharacters._select_ascii(limit)
+
+    assert len(selected) == expected_count
+    assert selected[0] == ASCII_PRINTABLE[0]
+    assert all(character in ASCII_PRINTABLE for character in selected)