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fix(mcp): stability fix pack — reload timeout, shutdown cleanup, event loop handler, OAuth non-blocking (#4757)

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Four fixes for MCP server stability issues reported by community member
(terminal lockup, zombie processes, escape sequence pollution, startup hang):

1. MCP reload timeout guard (cli.py): _check_config_mcp_changes now runs
   _reload_mcp in a separate daemon thread with a 30s hard timeout. Previously,
   a hung MCP server could block the process_loop thread indefinitely, freezing
   the entire TUI (user can type but nothing happens, only Ctrl+D/Ctrl+\ work).

2. MCP stdio subprocess PID tracking (mcp_tool.py): Tracks child PIDs spawned
   by stdio_client via before/after snapshots of /proc children. On shutdown,
   _stop_mcp_loop force-kills any tracked PIDs that survived the SDK's graceful
   SIGTERM→SIGKILL cleanup. Prevents zombie MCP server processes from
   accumulating across sessions.

3. MCP event loop exception handler (mcp_tool.py): Installs
   _mcp_loop_exception_handler on the MCP background event loop — same pattern
   as the existing _suppress_closed_loop_errors on prompt_toolkit's loop.
   Suppresses benign 'Event loop is closed' RuntimeError from httpx transport
   __del__ during MCP shutdown. Salvaged from PR #2538 (acsezen).

4. MCP OAuth non-blocking (mcp_oauth.py): Replaces blocking input() call in
   _wait_for_callback with OAuthNonInteractiveError raise. Adds _is_interactive()
   TTY detection. In non-interactive environments, build_oauth_auth() still
   returns a provider (cached tokens + refresh work), but the callback handler
   raises immediately instead of blocking the MCP event loop for 120s. Re-raises
   OAuth setup failures in _run_http so failed servers are reported cleanly
   without blocking others. Salvaged from PRs #4521 (voidborne-d) and #4465
   (heathley).

Closes #2537, closes #4462
Related: #4128, #3436
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Teknium 2026-04-03 02:29:20 -07:00 • committed by GitHub
parent f374ae4c61
commit cc54818d26
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5 changed files with 431 additions and 12 deletions
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13
cli.py
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@ -5016,11 +5016,18 @@ class HermesCLI:
return # mcp_servers unchanged (some other section was edited)
self._config_mcp_servers = new_mcp
# Notify user and reload
# Notify user and reload. Run in a separate thread with a hard
# timeout so a hung MCP server cannot block the process_loop
# indefinitely (which would freeze the entire TUI).
print()
print("🔄 MCP server config changed — reloading connections...")
with self._busy_command(self._slow_command_status("/reload-mcp")):
self._reload_mcp()
_reload_thread = threading.Thread(
target=self._reload_mcp, daemon=True
)
_reload_thread.start()
_reload_thread.join(timeout=30)
if _reload_thread.is_alive():
print(" ⚠️ MCP reload timed out (30s). Some servers may not have reconnected.")
def _reload_mcp(self):
"""Reload MCP servers: disconnect all, re-read config.yaml, reconnect.