Add optional charset restriction to InputField

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_widgets.py

@@ -94,3 +94,30 @@ def test_init_colors_survives_init_pair_rejecting_every_pair():
                        side_effect=_curses.error("init_pair() returned ERR")), \
          patch.object(_curses, "COLORS", 256, create=True):
         init_colors()      # must not raise
+
+
+def test_allowed_charset_accepts_listed_characters():
+    f = InputField(MagicMock(), 0, 0, 10, initial="", allowed="0123456789")
+    for ch in "90":
+        f.handle_key(ord(ch))
+    assert f.value == "90"
+
+
+def test_allowed_charset_drops_other_characters():
+    f = InputField(MagicMock(), 0, 0, 10, initial="", allowed="0123456789")
+    for ch in "9a0-!":
+        f.handle_key(ord(ch))
+    assert f.value == "90"
+
+
+def test_allowed_none_accepts_everything():
+    f = InputField(MagicMock(), 0, 0, 10, initial="")
+    for ch in "a-1!":
+        f.handle_key(ord(ch))
+    assert f.value == "a-1!"
+
+
+def test_allowed_charset_still_supports_editing_keys():
+    f = InputField(MagicMock(), 0, 0, 10, initial="90", allowed="0123456789")
+    f.handle_key(_curses.KEY_BACKSPACE)
+    assert f.value == "9"