diff --git a/tests/hermes_cli/test_regression_16767.py b/tests/hermes_cli/test_regression_16767.py
new file mode 100644
index 000000000..4aea5d640
--- /dev/null
+++ b/tests/hermes_cli/test_regression_16767.py
@@ -0,0 +1,58 @@
+import pytest
+import sys
+from unittest.mock import patch
+from pathlib import Path
+
+import hermes_cli.model_switch as ms
+from hermes_cli.model_switch import DirectAlias
+from hermes_cli.runtime_provider import _resolve_named_custom_runtime
+
+def test_ensure_direct_aliases_mutates_in_place(monkeypatch):
+    """_ensure_direct_aliases mutates DIRECT_ALIASES in place (guards against rebinding regression)."""
+    # Ensure we start with an empty but existing dict to check for mutation vs rebinding
+    ms.DIRECT_ALIASES.clear()
+    initial_id = id(ms.DIRECT_ALIASES)
+    
+    mock_data = {
+        "my-custom-alias": DirectAlias("custom-model:v1", "custom", "https://example.com/v1")
+    }
+    monkeypatch.setattr(ms, "_load_direct_aliases", lambda: mock_data)
+    
+    ms._ensure_direct_aliases()
+    
+    assert id(ms.DIRECT_ALIASES) == initial_id, f"DIRECT_ALIASES was rebound (ID changed from {initial_id} to {id(ms.DIRECT_ALIASES)})"
+    assert "my-custom-alias" in ms.DIRECT_ALIASES
+    assert ms.DIRECT_ALIASES["my-custom-alias"].model == "custom-model:v1"
+
+def test_chat_provider_argparse_acceptance(monkeypatch):
+    """chat --provider <user-defined> is accepted by argparse (guards against restrictive choices)."""
+    recorded: dict[str, str] = {}
+
+    # Mock cmd_chat to record the provider passed to it
+    def mock_cmd_chat(args):
+        recorded["provider"] = args.provider
+
+    monkeypatch.setattr("hermes_cli.main.cmd_chat", mock_cmd_chat)
+    monkeypatch.setattr(sys, "argv", ["hermes", "chat", "--provider", "my-custom-key"])
+
+    from hermes_cli.main import main
+    main()
+
+    assert recorded["provider"] == "my-custom-key"
+
+def test_resolve_named_custom_runtime_honors_explicit_base_url(monkeypatch):
+    """_resolve_named_custom_runtime honors (provider='custom', explicit_base_url=...)."""
+    # Mock has_usable_secret to recognize our test key
+    monkeypatch.setattr("hermes_cli.runtime_provider.has_usable_secret", lambda x: x == "test-api-key")
+    
+    result = _resolve_named_custom_runtime(
+        requested_provider="custom",
+        explicit_api_key="test-api-key",
+        explicit_base_url="http://example.test:1234/v1"
+    )
+    
+    assert result is not None
+    assert result["base_url"] == "http://example.test:1234/v1"
+    assert result["provider"] == "custom"
+    assert result["api_key"] == "test-api-key"
+    assert result["source"] == "direct-alias"