chore(mcp): drop the imports the deleted MCP death supervisor left behind

`sys` and `_get_mcp_stderr_log` in tools/mcp_tool.py were used only by _spawn_death_supervisor,
which this branch deleted (ruff: two new F401 against base). Three tests patched
tools.mcp_tool._get_mcp_stderr_log, which nothing reads now (the stdio transport reads
mcp_tool_config's directly, as it did on base), so those patches did nothing and go too. One slash
worker test still set HERMES_SLASH_WATCHDOG_GRACE_S/POLL_S, which nothing reads since the watchdog
knobs were removed.

tests/hermes_cli/test_process_identity_supervisor.py

@@ -619,7 +619,6 @@ def _stdio_connection(child_pid, fake_supervisor):
             side_effect=[set(), {child_pid}],
         ),
         patch("tools.mcp_tool_config._write_stderr_log_header"),
-        patch("tools.mcp_tool._get_mcp_stderr_log", return_value=None),
         patch(
             "hermes_cli.process_identity._spawn_supervisor",
             return_value=fake_supervisor,

tests/tools/test_mcp_stability.py

@@ -147,8 +147,6 @@ class TestStdioPidTracking:
                  patch("tools.mcp_tool_config._resolve_stdio_command",
                        return_value=("echo", {})), \
                  patch("tools.mcp_tool_config._write_stderr_log_header"), \
-                 patch("tools.mcp_tool._get_mcp_stderr_log",
-                       return_value=None), \
                  patch("tools.mcp_tool.check_package_for_malware",
                        return_value=None, create=True), \
                  patch("tools.osv_check.check_package_for_malware",

tests/tools/test_mcp_stdio_encoding_handler.py

@@ -45,7 +45,6 @@ class TestStdioEncodingErrorHandler:
                 patch("tools.mcp_tool.ClientSession", return_value=mock_session_cm),
                 patch("tools.mcp_tool_lifecycle._snapshot_child_pids", return_value=set()),
                 patch("tools.mcp_tool_config._write_stderr_log_header"),
-                patch("tools.mcp_tool._get_mcp_stderr_log", return_value=None),
             ):
                 server = MCPServerTask("test-encoding")
                 await server.start({

tests/tui_gateway/test_slash_worker_mcp_discovery.py

@@ -71,8 +71,6 @@ def test_profile_local_mcp_tool_is_visible_in_slash_worker(tmp_path):
             env.pop(key)
     env["HERMES_HOME"] = str(profile_home)
     env["PYTHONPATH"] = str(Path(__file__).resolve().parents[2])
-    env["HERMES_SLASH_WATCHDOG_GRACE_S"] = "0"
-    env["HERMES_SLASH_WATCHDOG_POLL_S"] = "0.05"
     proc = subprocess.Popen(
         [
             sys.executable,

tools/mcp_tool.py

@@ -16,7 +16,6 @@ import importlib.util
 import inspect
 import logging
 import os
-import sys
 import threading
 import time
 from typing import Any, Callable, Dict, List, Optional, Set
@@ -24,7 +23,7 @@ from typing import Any, Callable, Dict, List, Optional, Set
 logger = logging.getLogger(__name__)
 
 from tools.mcp_tool_common import _DEFAULT_TOOL_TIMEOUT, mcp_field
-from tools.mcp_tool_config import _get_mcp_stderr_log, _npx_cached_bin, _packaged_npx_entry
+from tools.mcp_tool_config import _npx_cached_bin, _packaged_npx_entry
 from tools.mcp_tool_sampling import ElicitationHandler, SamplingHandler
 from tools.mcp_tool_transport import MCPServerTransportMixin
 from tools.mcp_tool_server_run import MCPServerRunMixin