fix(grok): address adversarial-review findings across the grok-CLI conversion

A 7-dimension adversarial review (find -> independently refute) surfaced 14 real
issues; fixed each:

Runtime bugs
- GrokCliSession.send drained stdout fully BEFORE stderr — a >64KB stderr burst
  would deadlock the turn forever (spinner never clears). Drain stderr
  concurrently, and add a per-turn watchdog (ROBOCO_GROK_TURN_TIMEOUT_SECONDS,
  default 600s) that kills a wedged process and emits error+turn_end.
- Crash-restarted grok agents launched `grok -p ""` (empty prompt) — Claude gets
  a scan-for-work fallback. Default the prompt in _spawn_container so every
  dedicated provider gets it too.
- _grok_usage_json read /data/grok-usage unconditionally while its writers branch
  compose-vs-local, so a local-mode agent finalized at $0 and the cost-cap was
  inert. Single-source the path in a new _grok_usage_dir helper (read == write).
- GrokCliSession secretary role fell through to "unknown" (get_agent_role returns
  a truthy sentinel, never None), defeating the ROBOCO_AGENT_ROLE fallback.

Parity / hardening
- --deny set was missing `git tag -d` / `git reflog delete` that the Claude
  bash-guard blocks — added them (the "same set" claim is now true).
- Interactive mains now install the bash-guard hook too (defense-in-depth).
- Compose: collapse the GROK_AUTH_DIR / ROBOCO_HOST_GROK_DIR auth-mount pair into
  one canonical var so a partial override can't silently break agent auth.

Docs / comments
- Panel routing card + architecture security doc no longer say Grok runs on the
  deleted opencode runtime; orchestrator comments point at the renamed entrypoint.

Tests
- Cover the interactive _render_grok_config MCP wiring (ModuleNotFound guard +
  secretary HMAC env), the cost-cap kill-failure + interactive relay-close paths,
  the local-mode usage read, the role fallback, the turn timeout, and the new
  git denies. (#13 — a separate grok "Write" tool — investigated: grok's only
  built-in file-mutation tool is search_replace, already removed; no gap.)

Gate green: ruff, mypy, xenon, tests.

tests/unit/runtime/test_grok_usage_finalize.py

@@ -10,10 +10,12 @@ output (it bills at the output rate).
 from __future__ import annotations
 
 import json
+import tempfile
 from typing import TYPE_CHECKING
 
 import pytest
 from roboco.models.runtime import AgentInstance
+from roboco.runtime import orchestrator as orch_mod
 from roboco.runtime.orchestrator import AgentOrchestrator
 
 if TYPE_CHECKING:
@@ -75,3 +77,35 @@ async def test_resolve_final_usage_routes_grok_to_usage_json(
 
     # No SDK fetch / transcript read for GROK — usage comes from usage.json.
     assert await orch._resolve_final_token_usage("be-dev-1") == (0, 12, 0, 0)
+
+
+def test_grok_usage_dir_branches_compose_vs_local(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setattr(orch_mod, "PROJECT_HOST_PATH", "")
+    local = AgentOrchestrator._grok_usage_dir("be-dev-1")
+    assert "roboco-grok-usage" in str(local)
+    assert local.name == "be-dev-1"
+
+    monkeypatch.setattr(orch_mod, "PROJECT_HOST_PATH", "/volume1/roboco")
+    monkeypatch.setattr(orch_mod, "GROK_USAGE_DATA_DIR", "/data/grok-usage")
+    assert str(AgentOrchestrator._grok_usage_dir("be-dev-1")) == (
+        "/data/grok-usage/be-dev-1"
+    )
+
+
+def test_grok_usage_json_reads_the_real_local_dir(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    # The un-mocked read path must find usage.json in the SAME branched dir the
+    # writer mounts (the local-mode fix: read side mirrors the write side).
+    monkeypatch.setattr(orch_mod, "PROJECT_HOST_PATH", "")
+    monkeypatch.setattr(tempfile, "gettempdir", lambda: str(tmp_path))
+    udir = tmp_path / "roboco-grok-usage" / "be-dev-1"
+    udir.mkdir(parents=True)
+    (udir / "usage.json").write_text(
+        json.dumps({"total_tokens": 55, "cost_usd": 0.1}), encoding="utf-8"
+    )
+    orch = AgentOrchestrator.__new__(AgentOrchestrator)
+    assert orch._grok_usage_tokens("be-dev-1") == (0, 55, 0, 0)
+    assert orch._grok_cost_usd("be-dev-1") == 0.1  # noqa: PLR2004