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.

hermes_cli/runtime_provider.py

@@ -491,27 +491,15 @@ def _lift_max_output_tokens(entry: Dict[str, Any], result: Dict[str, Any]) -> No
 
 def _get_named_custom_provider(requested_provider: str) -> Optional[Dict[str, Any]]:
     requested_norm = _normalize_custom_provider_name(requested_provider or "")
-    if not requested_norm:
+    if not requested_norm or requested_norm == "custom":
         return None
 
-    # Bare "custom" is normally an incomplete spec — the canonical form is
-    # "custom:<name>" — and is otherwise owned by the model.base_url "bare
-    # custom" trust path. BUT a user may literally name a ``providers:`` (or
-    # legacy ``custom_providers:``) entry "custom" (e.g. ``providers.custom``
-    # pointing at cliproxy). We used to return None here *before* scanning
-    # config, so such an entry was never matched and resolution fell through to
-    # the global default (Codex) — the cause of cron jobs with
-    # ``provider: "custom"`` failing with ``auth_unavailable: providers=codex``.
-    # Fall through to the config scan instead; if no entry is literally named
-    # "custom" it still returns None at the end, preserving the trust path.
-
     # Raw names should only map to custom providers when they are not already
     # valid built-in providers or aliases. Explicit menu keys like
-    # ``custom:local`` always target the saved custom provider. Bare "custom"
-    # is exempt from the shadow check — it is not a built-in to defer to.
+    # ``custom:local`` always target the saved custom provider.
     if requested_norm == "auto":
         return None
-    if requested_norm != "custom" and not requested_norm.startswith("custom:"):
+    if not requested_norm.startswith("custom:"):
         try:
             canonical = auth_mod.resolve_provider(requested_norm)
         except AuthError:
@@ -646,20 +634,6 @@ def _get_named_custom_provider(requested_provider: str) -> Optional[Dict[str, An
     return None
 
 
-def has_named_custom_provider(requested_provider: str) -> bool:
-    """Return True when config defines a custom provider matching the request.
-
-    Thin public wrapper around :func:`_get_named_custom_provider` so other
-    modules (e.g. the cronjob tool) can decide whether a provider name will
-    actually resolve to a configured ``providers:`` / ``custom_providers:``
-    entry — without reaching into a private helper or duplicating the scan.
-    """
-    try:
-        return _get_named_custom_provider(requested_provider) is not None
-    except Exception:
-        return False
-
-
 def _custom_provider_request_overrides(custom_provider: Dict[str, Any]) -> Dict[str, Any]:
     extra_body = custom_provider.get("extra_body")
     if not isinstance(extra_body, dict) or not extra_body: