opentui(phase3): launcher integration — HERMES_TUI_ENGINE dual-engine

hermes --tui launches the native OpenTUI engine (Bun) when
HERMES_TUI_ENGINE=opentui (env) or display.tui_engine=opentui (config);
Ink stays the default and the shipping path is untouched.

- _resolve_tui_engine() (env > config > ink); refuses opentui on
  Windows/Termux (no Bun) -> falls back to ink with a notice.
- _make_opentui_argv() -> [bun, src/entry.real.tsx] (no build step).
- _bun_bin() with HERMES_BUN override.
- Branch at top of _make_tui_argv BEFORE _ensure_tui_node (Bun-only host
  must not bootstrap Node).
- Gate _launch_tui NODE_OPTIONS/--max-old-space-size on engine==ink (Bun
  is JSC; the V8 flag errors/ignores).

Verified end-to-end via tmux: real hermes --tui -> Bun -> OpenTUI ->
real Python gateway streamed a real reply. No-flag default still ink.

tests/gateway/test_telegram_model_picker.py

@@ -91,6 +91,10 @@ class TestTelegramModelPicker:
         query.answer = AsyncMock()
         query.edit_message_text = AsyncMock()
 
+        update = MagicMock()
+        update.callback_query = query
+        context = MagicMock()
+
         await adapter._handle_model_picker_callback(query, "mb", "12345")
 
         edit_kwargs = query.edit_message_text.call_args[1]
@@ -129,11 +133,17 @@ class TestTelegramModelPicker:
 
         await adapter._handle_model_picker_callback(query, "mm:0", "12345")
 
+        # The callback was invoked with the selected model
         callback.assert_awaited_once()
+        # edit_message_text MUST be called on the success path (this is the
+        # regression we're guarding).
         query.edit_message_text.assert_awaited()
         edit_kwargs = query.edit_message_text.call_args[1]
         assert "MARKDOWN_V2" in repr(edit_kwargs["parse_mode"])
+        # The dynamic result text was routed through format_message
+        # (backtick code blocks survive escaping).
         assert "`gpt-5`" in edit_kwargs["text"]
+        # State is cleaned up after a successful switch.
         assert "12345" not in adapter._model_picker_state
 
     @pytest.mark.asyncio
@@ -174,7 +184,7 @@ class TestTelegramModelPicker:
         providers = [
             {"slug": "minimax", "name": "MiniMax", "total_models": 2},
             {"slug": "minimax-cn", "name": "MiniMax (China)", "total_models": 3},
-            {"slug": "xai", "name": "xAI", "total_models": 1},
+            {"slug": "xai", "name": "xAI", "total_models": 1},  # lone group member
         ]
 
         await adapter.send_model_picker(
@@ -187,11 +197,14 @@ class TestTelegramModelPicker:
             metadata=None,
         )
 
+        # Top-level keyboard: MiniMax family folded into one group button;
+        # xai (lone member) degraded to a direct provider button.
         assert "mpg:minimax" in built
         assert "mp:xai" in built
         assert "mp:minimax" not in built
         assert "mp:minimax-cn" not in built
 
+        # Drill into the MiniMax group → members appear as mp: buttons + back.
         built.clear()
         query = AsyncMock()
         query.message = MagicMock()
@@ -203,49 +216,7 @@ class TestTelegramModelPicker:
 
         assert "mp:minimax" in built
         assert "mp:minimax-cn" in built
-        assert "mb" in built
-
-    @pytest.mark.asyncio
-    async def test_expensive_model_requires_confirmation(self, monkeypatch):
-        adapter = _make_adapter()
-        callback = AsyncMock(return_value="Switched to `openai/gpt-5.5-pro`")
-        adapter._model_picker_state["12345"] = {
-            "providers": [
-                {"slug": "openrouter", "name": "OpenRouter", "total_models": 1, "is_current": True}
-            ],
-            "current_model": "model_1",
-            "current_provider": "openrouter",
-            "session_key": "s",
-            "on_model_selected": callback,
-            "selected_provider": "openrouter",
-            "model_list": ["openai/gpt-5.5-pro"],
-            "msg_id": 42,
-        }
-        monkeypatch.setattr(
-            "hermes_cli.model_cost_guard.expensive_model_warning",
-            lambda *_args, **_kwargs: SimpleNamespace(
-                message="!!! EXPENSIVE MODEL WARNING !!!\ndid you mean to select openai/gpt-5.5?"
-            ),
-        )
-
-        query = AsyncMock()
-        query.message = MagicMock()
-        query.message.chat_id = 12345
-        query.answer = AsyncMock()
-        query.edit_message_text = AsyncMock()
-
-        await adapter._handle_model_picker_callback(query, "mm:0", "12345")
-
-        callback.assert_not_awaited()
-        assert "12345" in adapter._model_picker_state
-        first_edit = query.edit_message_text.call_args[1]
-        assert "EXPENSIVE MODEL WARNING" in first_edit["text"]
-        assert first_edit["reply_markup"] is not None
-
-        await adapter._handle_model_picker_callback(query, "mc:0", "12345")
-
-        callback.assert_awaited_once_with("12345", "openai/gpt-5.5-pro", "openrouter")
-        assert "12345" not in adapter._model_picker_state
+        assert "mb" in built  # back-to-providers button present
 
     @pytest.mark.asyncio
     async def test_retries_without_thread_when_thread_not_found(self):