MCP server processes not terminated on agent session end

[a4xrbj1]

Steps to reproduce

1. Run a multi-agent session with MCP servers configured (e.g. MongoDB MCP)
2. Let the session complete, or kill the coordinator
3. Run ps aux | grep mcp-server

Expected behavior

All MCP server processes are terminated when the agent session or coordinator that spawned them exits.

MCP server processes remain running indefinitely. After several multi-agent runs, 20+ orphaned instances were found:

ps aux | grep mongodb-mcp-server
andreaswest  53222  ... node .../mongodb-mcp-server --readOnly --connectionString mongodb://localhost:27017/worker
andreaswest  25472  ... node .../mongodb-mcp-server
andreaswest  21498  ... node .../mongodb-mcp-server --readOnly --connectionString mongodb://localhost:27017/worker
# ... 18 more instances

All orphaned processes had PPID 1 (reparented to launchd), confirming the parent agent process exited without cleaning up its children.

Impact

• Sustained high CPU and memory usage between sessions
• fseventsd thrashing from open file handles across worktrees
• System load average remained elevated (25+) long after all sessions were stopped
• Required manual pkill -f mongodb-mcp-server to recover

Suggested fix

Agent teardown (session-end hook, coordinator stop, and crash recovery paths) should explicitly terminate any MCP server child processes. A process group kill (kill -TERM -<pgid>) on the spawned process group would catch all descendants. Alternatively, tracking spawned MCP PIDs in the .overstory/ SQLite DB and killing them on cleanup would also work.

A ov clean command that kills known orphaned MCP/agent processes would also be a useful complement.

Workaround

pkill -f mongodb-mcp-server

Actual behavior

Summary

When agent sessions end (normally or via crash/interrupt), MCP server child processes are not terminated. They accumulate as orphaned processes reparented to launchd, consuming memory and CPU indefinitely.

overstory version

0.9.1

Bun version

1.3.10

Operating system

macOS 26.3.1