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.

agent/bedrock_adapter.py

@@ -208,41 +208,6 @@ def is_stale_connection_error(exc: BaseException) -> bool:
     return False
 
 
-def is_streaming_access_denied_error(exc: BaseException) -> bool:
-    """Return True when AWS denied the ``bedrock:InvokeModelWithResponseStream`` action.
-
-    IAM policies scoped to ``bedrock:InvokeModel`` only (a common least-privilege
-    setup) reject ``converse_stream()`` with an ``AccessDeniedException`` whose
-    message names the streaming action, e.g.::
-
-        User: arn:aws:iam::123456789012:user/x is not authorized to perform:
-        bedrock:InvokeModelWithResponseStream on resource: ...
-
-    This is permanent for the session — retrying the stream can never succeed —
-    so callers should flip to the non-streaming ``converse()`` path (which maps
-    to ``bedrock:InvokeModel``) instead of burning retries.
-
-    Detection is deliberately message-based: boto3 surfaces this as a
-    ``ClientError`` with ``Error.Code == "AccessDeniedException"``, and the
-    AnthropicBedrock SDK wraps the same AWS response in its own exception
-    types, but both preserve the action name in the message.
-    """
-    msg = str(exc).lower()
-    if "invokemodelwithresponsestream" not in msg:
-        return False
-    # ClientError with an explicit access-denied code is the canonical form.
-    try:
-        from botocore.exceptions import ClientError
-    except ImportError:  # pragma: no cover — botocore always present with boto3
-        ClientError = None  # type: ignore[assignment]
-    if ClientError is not None and isinstance(exc, ClientError):
-        code = (getattr(exc, "response", None) or {}).get("Error", {}).get("Code", "")
-        return code in ("AccessDeniedException", "UnauthorizedException")
-    # Wrapped forms (e.g. AnthropicBedrock SDK PermissionDeniedError) — match
-    # on the authorization-failure phrasing AWS uses.
-    return "not authorized" in msg or "accessdenied" in msg
-
-
 # ---------------------------------------------------------------------------
 # AWS credential detection
 # ---------------------------------------------------------------------------
@@ -1038,16 +1003,6 @@ def call_converse_stream(
     try:
         response = client.converse_stream(**kwargs)
     except Exception as exc:
-        if is_streaming_access_denied_error(exc):
-            # IAM allows bedrock:InvokeModel but not
-            # InvokeModelWithResponseStream — permanent for this session.
-            # Fall back to the non-streaming converse() path.
-            logger.info(
-                "bedrock: converse_stream denied by IAM on (region=%s, model=%s) — "
-                "falling back to non-streaming converse().",
-                region, model,
-            )
-            return normalize_converse_response(client.converse(**kwargs))
         if is_stale_connection_error(exc):
             logger.warning(
                 "bedrock: stale-connection error on converse_stream(region=%s, "