feat: Add separate MCP server package

[nzakas]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

Adds a new @eslint/mcp package.

What changes did you make? (Give an overview)

• Ported mcp-server.js from the eslint repo, along with tests.
• Updated related files for the monorepo to reflect the new package

Related Issues

refs eslint/eslint#19682

Is there anything you'd like reviewers to focus on?

This package has no JSR equivalent because it's a binary.

Also, because it's a binary, I'm not rolling up or converting to CommonJS. It stays ESM and the src directory is published.

These were simplifying decisions based on the uniqueness of this package. I think this is okay because there is no API exposed through the package.

[nzakas]

The failure is a Mocha timeout. Seems intermittent.

[Copilot]

Pull Request Overview

This PR adds a new @eslint/mcp package that implements an MCP server for ESLint along with its CLI and accompanying tests and configuration updates.

• Port the existing mcp-server.js into the new package with a corresponding CLI executable.
• Add tests for both the MCP server and CLI, as well as update documentation, workflows, and issue templates to support the new package.

Reviewed Changes

Copilot reviewed 15 out of 19 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/mcp/tests/mcp-server.test.js	Added tests for MCP server tools functionality
packages/mcp/tests/mcp-cli.js	Added CLI tests to verify startup behavior
packages/mcp/tests/fixtures/*	Added fixture files for testing linting outcomes
packages/mcp/src/mcp-server.js	Implemented the MCP server using ESLint integration
packages/mcp/src/mcp-cli.js	Provided a CLI to initialize and run the MCP server
packages/mcp/README.md	Updated documentation to include usage for the new package
Other configuration files (.github/workflows, etc.)	Updated CI/workflows and issue templates to include the MCP package

Files not reviewed (4)

• .release-please-manifest.json: Language not supported
• packages/mcp/package.json: Language not supported
• packages/mcp/tsconfig.json: Language not supported
• release-please-config.json: Language not supported

[mdjermanovic]

LGTM, thanks! Leaving open for @fasttime to verify.

[fasttime]

Suggested change

	// Important: Cursor throws an error when `describe()` is used in the schema.
	const filePathsSchema = {
	filePaths: z.array(z.string().min(1)).nonempty(),
	};
	const filePathsSchema = {
	filePaths: z
	.array(
	z
	.string()
	.min(1)
	.describe("Full filesystem path of a file to be analyzed"),
	)
	.nonempty(),
	};

I can't reproduce the error in Cursor anymore. I tried to re-add the description from this commit and I configured Cursor to start the server directly from the path of mcp-cli.js. I can see that lint-file is working as expected now. How is it for you?

[nzakas]

I'd prefer to stick with what we knew already worked in the previous release in this PR. We can make other changes like this as improvements later.

[fasttime]

LGTM, thanks!