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/context_references.py

@@ -246,14 +246,7 @@ def _expand_file_reference(
     if not path.is_file():
         return f"{ref.raw}: path is not a file", None
     if _is_binary_file(path):
-        # A binary file can't be inlined as text, but it IS on disk (the agent's
-        # tools run where this resolves — the local cwd, or the staged copy in a
-        # remote session workspace). Returning a bare "not supported" warning
-        # with no content was a dead end: the model saw a failure and gave up
-        # (told the user the file type wasn't supported). Instead, hand it an
-        # actionable block — the path, type, size, and a nudge to use its tools —
-        # so it can read/convert/view the file itself.
-        return None, _binary_reference_block(ref, path)
+        return f"{ref.raw}: binary files are not supported", None
 
     text = path.read_text(encoding="utf-8")
     if ref.line_start is not None:
@@ -297,7 +290,6 @@ def _expand_git_reference(
             capture_output=True,
             text=True,
             timeout=30,
-            stdin=subprocess.DEVNULL,
         )
     except subprocess.TimeoutExpired:
         return f"{ref.raw}: git command timed out (30s)", None
@@ -490,7 +482,6 @@ def _rg_files(path: Path, cwd: Path, limit: int) -> list[Path] | None:
             capture_output=True,
             text=True,
             timeout=10,
-            stdin=subprocess.DEVNULL,
         )
     except (FileNotFoundError, OSError, subprocess.TimeoutExpired):
         return None
@@ -500,30 +491,6 @@ def _rg_files(path: Path, cwd: Path, limit: int) -> list[Path] | None:
     return files[:limit]
 
 
-def _human_bytes(n: int) -> str:
-    size = float(n)
-    for unit in ("B", "KB", "MB", "GB"):
-        if size < 1024 or unit == "GB":
-            return f"{int(size)} {unit}" if unit == "B" else f"{size:.1f} {unit}"
-        size /= 1024
-    return f"{size:.1f} GB"
-
-
-def _binary_reference_block(ref: ContextReference, path: Path) -> str:
-    mime, _ = mimetypes.guess_type(path.name)
-    mime = mime or "application/octet-stream"
-    try:
-        size = _human_bytes(path.stat().st_size)
-    except OSError:
-        size = "unknown size"
-    return (
-        f"📎 {ref.raw} ({mime}, {size}) — binary file, not inlined as text. "
-        f"It is available on disk at `{path}`. Use your tools to work with it "
-        f"(read or convert it, extract its text, or view/render it as needed); "
-        f"do not tell the user the file type is unsupported."
-    )
-
-
 def _file_metadata(path: Path) -> str:
     if _is_binary_file(path):
         return f"{path.stat().st_size} bytes"