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.

model_tools.py

@@ -253,14 +253,6 @@ _LEGACY_TOOLSET_MAP = {
 # daemon start/stop, env var changes, etc.) on a 30 s horizon.
 _tool_defs_cache: Dict[tuple, List[Dict[str, Any]]] = {}
 
-# Hard cap on memoized get_tool_definitions() results. A long-lived Gateway
-# process sees many distinct toolset/config fingerprints over its lifetime
-# (per-session toolset sets, config edits, kanban-task toggles); without a
-# bound the cache grows unboundedly. 8 comfortably covers the warm working
-# set (the handful of distinct platform/toolset combos a gateway actually
-# serves) while keeping the cap small. (#19251)
-_TOOL_DEFS_CACHE_MAX = 8
-
 
 def _clear_tool_defs_cache() -> None:
     """Drop memoized get_tool_definitions() results. Called when dynamic
@@ -337,11 +329,6 @@ def get_tool_definitions(
         # agent inits and providers that enforce unique tool names
         # (DeepSeek, Xiaomi MiMo, Moonshot Kimi) reject the request with
         # HTTP 400. Mirrors the cache-hit path above. (issue #17335)
-        # Bound the cache with LRU eviction so a long-lived Gateway process
-        # doesn't accumulate entries unboundedly across the many distinct
-        # toolset/config fingerprints it sees over its lifetime (#19251).
-        if len(_tool_defs_cache) >= _TOOL_DEFS_CACHE_MAX:
-            _tool_defs_cache.pop(next(iter(_tool_defs_cache)))  # evict oldest
         _tool_defs_cache[cache_key] = result
         return list(result)
     return result