MCP Persistent Connections

[ngafar]

Description

Every time the AI needed to know what MCP tools were available — or actually call one — the code would:

1. Spawn a new subprocess (starting the MCP server from scratch)
2. Do a handshake
3. Ask "what tools do you have?"
4. Do the work
5. Kill the process

This happened on every single AI message that involved MCP tools.

The old approach meant each agent loop was paying subprocess startup cost plus a tools/list round-trip on top of that. With many tools across several servers, this adds up fast and makes the agent feel sluggish.

What we've done is the same basic idea as a database connection pool: you pay the setup cost once, then reuse the connection for the lifetime of the session.

Testing

1. Visit the MCP settings page, and confirm you can still connect to servers.
2. Have the Agent use and MCP server.
3. Have the Agent use the same sever a second time.

In theory, multiple calls to the same MCP server should be faster, this is hard to test without proper benchmarks. However, the logic behind the persistent connections is sound.

Documentation

N/A - BTS changes

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Note

Medium Risk
Changes how long-lived MCP child processes are managed; stale sessions, leaked subprocesses, or incorrect invalidation could affect agent tool calls until reconnect, though errors trigger eviction and delete clears the pool entry.

Overview
Replaces per-call MCP subprocess spawn with a persistent connection pool keyed by server_id, so listing tools and invoking tools reuse one stdio ClientSession instead of starting the server on every agent message.

MCPConnectionManager holds sessions, configs, per-server locks, and a cached tool list; failures and timeouts evict the session so the next call reconnects. Short-lived connections remain only when server_id is omitted (e.g. validating a new server on POST).

Call sites now pass server_id from the JupyterLab tool executor, MCP settings GET, and get_available_mcp_tools. Deleting an MCP server is async and invalidates the pooled connection for that id.

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Project	Deployment	Actions	Updated (UTC)
monorepo	Ready	Preview, Comment	Jun 22, 2026 5:32pm

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Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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