Load the MCP client SDK lazily on first outbound connection

[RhysSullivan]

Follow-up to #1742. That patch removed the eager schema preload, but the statically-imported @modelcontextprotocol/client barrel still costs ~11MB of heap plus module-eval CPU per isolate, and @modelcontextprotocol/core (imported for one JSON schema) another ~8.6MB. Post-#1742 traces show the remaining p95 tail is entirely first-request-on-fresh-isolate cost: session verify p50 is 2.5s on isolates whose JWKS cache was empty at start and 0ms otherwise.

• client-module.ts lazy-loads and memoizes the client barrel + cf-worker validator on first outbound connect, mirroring the existing stdio dynamic import. Isolates that never dial an MCP server never load it.
• Synchronous error classification (SdkHttpError.isInstance etc.) consults the loader's mcpClientSdkIfLoaded: errors of those classes are only constructed by the loaded module, so "not loaded" soundly means "not an SDK error".
• The call-tool-result output schema is baked into a generated file (call-tool-result-schema.gen.ts + drift test + regen script), removing the runtime @modelcontextprotocol/core import entirely — it was needed for exactly one schema, including on cached-catalog paths that never connect.

In the built cloud worker, the client chunk is now reachable only through dynamic import (via the execution stack, itself lazy); it was previously in the eager first-request graph.

Verify after deploy: isolate reuse (requests per service.instance.id) up from ~4-5, and cold-isolate local_verify p50 down from ~2.5s in the executor-cloud dataset.

[cloudflare-workers-and-pages]

Deploying with    Cloudflare Workers

The latest updates on your project. Learn more about integrating Git with Workers.

Status	Name	Latest Commit	Updated (UTC)
✅ Deployment successful! View logs	executor-cloud	e6eaeff	Aug 25 2026, 09:50 PM

[github-actions]

Cloudflare preview

Torn down — the PR is closed.

[pkg-pr-new]

Open in StackBlitz

@executor-js/cli

npm i https://pkg.pr.new/@executor-js/cli@1747

@executor-js/config

npm i https://pkg.pr.new/@executor-js/config@1747

@executor-js/execution

npm i https://pkg.pr.new/@executor-js/execution@1747

@executor-js/sdk

npm i https://pkg.pr.new/@executor-js/sdk@1747

@executor-js/codemode-core

npm i https://pkg.pr.new/@executor-js/codemode-core@1747

@executor-js/runtime-quickjs

npm i https://pkg.pr.new/@executor-js/runtime-quickjs@1747

@executor-js/plugin-file-secrets

npm i https://pkg.pr.new/@executor-js/plugin-file-secrets@1747

@executor-js/plugin-graphql

npm i https://pkg.pr.new/@executor-js/plugin-graphql@1747

@executor-js/plugin-keychain

npm i https://pkg.pr.new/@executor-js/plugin-keychain@1747

@executor-js/plugin-mcp

npm i https://pkg.pr.new/@executor-js/plugin-mcp@1747

@executor-js/plugin-onepassword

npm i https://pkg.pr.new/@executor-js/plugin-onepassword@1747

@executor-js/plugin-openapi

npm i https://pkg.pr.new/@executor-js/plugin-openapi@1747

executor

npm i https://pkg.pr.new/executor@1747

commit: e6eaeff

[cloudflare-workers-and-pages]

Deploying with    Cloudflare Workers

The latest updates on your project. Learn more about integrating Git with Workers.

Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	executor-marketing	e6eaeff	Commit Preview URL Branch Preview URL	Aug 25 2026, 09:48 PM