fix: preserve empty dict allow_from handling

Keep dict-backed channel configs compatible with both allow_from and allowFrom without losing empty-list semantics, and add focused regression coverage for the allow-list boundary.

Made-with: Cursor

tests/channels/test_base_channel.py

@@ -23,3 +23,15 @@ def test_is_allowed_requires_exact_match() -> None:
 
     assert channel.is_allowed("allow@email.com") is True
     assert channel.is_allowed("attacker|allow@email.com") is False
+
+
+def test_is_allowed_supports_dict_allow_from_alias() -> None:
+    channel = _DummyChannel({"allowFrom": ["alice"]}, MessageBus())
+
+    assert channel.is_allowed("alice") is True
+
+
+def test_is_allowed_denies_empty_dict_allow_from() -> None:
+    channel = _DummyChannel({"allow_from": []}, MessageBus())
+
+    assert channel.is_allowed("alice") is False