feat(mcp): reuse warm connections for tool execution and discovery

[waleedlatif1]

Summary

• Adds a warm MCP connection pool so tool execution and discovery reuse a live connection per server instead of connecting, initializing, and tearing down on every call (the connect-per-operation pattern behind the systemic -32001 request timeouts)
• One warm connection per server, keyed by server id; concurrent requests multiplex over the single transport (verified against the MCP SDK, LibreChat, Cline, VS Code)
• Single-flight creation (concurrent misses share one connect), 60s liveness ping-cache, and eviction on config change, max age (re-resolves the pinned SSRF IP), idle timeout, transport close, and session error
• Wires all four connect-per-op sites through one withServerClient seam; calls carrying per-request headers bypass the pool (can't share a connection under different headers)
• Reconnect stays demand-driven via the callers' existing retry — no background reconnect loop. On by default, no flag

Type of Change

• New feature

Testing

• Added connection-pool.test.ts (12) and service-pool.test.ts (3); full MCP suite green (347 tests), tsc clean, boundary audit at baseline
• Not yet exercised against a live server under load — will watch pool-hit / timeout metrics after deploy

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Jul 19, 2026 1:50am

[cursor]

PR Summary

Medium Risk
Changes core MCP hot paths (long-lived sockets, shared transports, credential-scoped pooling) and lifecycle eviction; behavior is heavily tested but not yet validated under production load.

Overview
Replaces connect-per-operation for MCP tool execution and tools/list discovery with a warm connection pool keyed by server, workspace, and user so credentials from env resolution are never shared across users.

McpConnectionPool leases ref-counted clients with single-flight creation, 60s liveness ping cache (5s ping timeout via updated McpClient.ping), max age, idle eviction, LRU cap, and safe retirement while borrowers are active. Failed ops poison the lease; config changes use evictServerConnections (wired from server update/delete lifecycle), separate from tool cache clearCache.

McpService centralizes access in withServerClient: pool hits skip reconnect and env/SSRF work; per-request extraHeaders bypass the pool; dead-connection and auth errors retire connections and trigger existing retries (including one-shot credential rotation for headers auth on discovery/execute).

Broad unit/integration tests cover pool races and service wiring.

^{Reviewed by Cursor Bugbot for commit d74d48d. Configure here.}

[greptile-apps]

Greptile Summary

This PR adds reusable warm connections for MCP tool execution and discovery. The main changes are:

• Adds an auth-scoped connection pool with single-flight creation and liveness checks.
• Defers connection shutdown until active borrowers finish.
• Rebuilds connections after config, session, transport, or credential failures.
• Routes tool execution and discovery through a shared client lease.
• Keeps per-request-header calls on isolated connections.
• Adds pool, lifecycle, retry, and credential-rotation tests.

Confidence Score: 5/5

This looks safe to merge.

• The updated lifecycle guards keep active requests alive during retirement.
• Stale close events cannot evict replacement connections.
• Pool keys separate workspace and user credential contexts.
• Authentication failures retire stale connections and retry with freshly resolved credentials.
• No blocking issues were found in the changed code.

Important Files Changed

Filename	Overview
apps/sim/lib/mcp/connection-pool.ts	Adds pooled connection creation, reuse, liveness checks, retirement, eviction, and deferred shutdown.
apps/sim/lib/mcp/service.ts	Uses pooled clients for execution and discovery, scopes connections by auth context, and retries stale credentials.
apps/sim/lib/mcp/orchestration/server-lifecycle.ts	Evicts warm connections after server configuration changes and deletion.
apps/sim/lib/mcp/client.ts	Adds an optional timeout for MCP liveness pings.

_{Reviews (13): Last reviewed commit: "chore(mcp): add debug logging for pool h..." | Re-trigger Greptile}

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit 0edd043. Configure here.}

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit 65bd1f3. Configure here.}

[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit d74d48d. Configure here.}