fix(tui): guard personality overlay when personalities is null

TUI auto-resolves `display.personality` at session init, unlike the base CLI.
If config contains `agent.personalities: null`, `_resolve_personality_prompt`
called `.get()` on None and failed before model/provider selection.
Normalize null personalities to `{}` and surface a targeted config warning.

tests/tui_gateway/test_make_agent_provider.py

@@ -67,11 +67,25 @@ def test_probe_config_health_flags_null_sections():
     assert "model" not in msg
 
 
+def test_probe_config_health_flags_null_personalities_with_active_personality():
+    from tui_gateway.server import _probe_config_health
+
+    msg = _probe_config_health(
+        {
+            "agent": {"personalities": None},
+            "display": {"personality": "kawaii"},
+            "model": {},
+        }
+    )
+    assert "display.personality" in msg
+    assert "agent.personalities" in msg
+
+
 def test_make_agent_tolerates_null_config_sections():
     """Bare `agent:` / `display:` keys in ~/.hermes/config.yaml parse as
     None. cfg.get("agent", {}) returns None (default only fires on missing
     key), so downstream .get() chains must be guarded. Reported via Twitter
-    against the new TUI; CLI path is unaffected."""
+    against the new TUI."""
 
     fake_runtime = {
         "provider": "openrouter",
@@ -99,3 +113,37 @@ def test_make_agent_tolerates_null_config_sections():
         _make_agent("sid-null", "key-null")
 
         assert mock_agent.called
+
+
+def test_make_agent_tolerates_null_personalities_with_active_personality():
+    fake_runtime = {
+        "provider": "openrouter",
+        "base_url": "https://api.synthetic.new/v1",
+        "api_key": "sk-test",
+        "api_mode": "chat_completions",
+        "command": None,
+        "args": None,
+        "credential_pool": None,
+    }
+    cfg = {
+        "agent": {"personalities": None},
+        "display": {"personality": "kawaii"},
+        "model": {"default": "glm-5"},
+    }
+
+    with (
+        patch("tui_gateway.server._load_cfg", return_value=cfg),
+        patch("tui_gateway.server._get_db", return_value=MagicMock()),
+        patch("cli.load_cli_config", return_value={"agent": {"personalities": None}}),
+        patch(
+            "hermes_cli.runtime_provider.resolve_runtime_provider",
+            return_value=fake_runtime,
+        ),
+        patch("run_agent.AIAgent") as mock_agent,
+    ):
+        from tui_gateway.server import _make_agent
+
+        _make_agent("sid-null-personality", "key-null-personality")
+
+        assert mock_agent.called
+        assert mock_agent.call_args.kwargs["ephemeral_system_prompt"] is None