Fix internal stdio-based MCP server

[JReinhold]

#54 introduced a requirement that the original web request be passed into the server context on every request. Unfortunately this broke the stdio-based MCP server as that doesn't have a web request associated. The stdio-based MCP server is only used internally in evals.

This PR changes it so that the web request is only required when using the default manifest provider. If you set a custom manifest provider (like our stdio MCP does), it's okay to not pass the request, as it's then up to you to decide how to get the manifest with what information.

Our stdio MCP then takes advantage of this.

Also added integration tests to our stdio MCP to ensure it doesn't break in the future.

[changeset-bot]

🦋 Changeset detected

Latest commit: 1e49e69

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[pkg-pr-new]

npm i https://pkg.pr.new/@storybook/addon-mcp@85

npm i https://pkg.pr.new/@storybook/mcp@85

commit: 1e49e69

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 38.57%. Comparing base (5d18405) to head (1e49e69).
⚠️ Report is 1 commits behind head on next.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
packages/mcp/src/utils/get-manifest.ts	50.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next      #85      +/-   ##
==========================================
- Coverage   38.77%   38.57%   -0.21%     
==========================================
  Files          23       23              
  Lines         686      687       +1     
  Branches      167      169       +2     
==========================================
- Hits          266      265       -1     
  Misses        390      390              
- Partials       30       32       +2     

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[Copilot]

Pull Request Overview

This PR fixes a regression introduced in #54 where the stdio-based MCP server (used for internal evaluations) broke because it doesn't have a web request to pass to the server context. The fix makes the request parameter optional when using a custom manifestProvider, since custom providers can retrieve manifests without needing the HTTP request object.

Key changes:

• Modified manifestProvider signature to accept Request | undefined instead of requiring Request
• Moved request validation into the default manifest provider (where it's actually needed)
• Updated error messages to guide users when request is missing
• Added integration tests for the stdio MCP server to prevent future regressions

Reviewed Changes

Copilot reviewed 6 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/mcp/src/utils/get-manifest.ts	Made request parameter optional, moved validation to default provider, improved error handling
packages/mcp/src/utils/get-manifest.test.ts	Updated tests for optional request parameter, added test for custom provider without request
packages/mcp/src/types.ts	Updated manifestProvider signature to accept optional request parameter
packages/mcp/bin.test.ts	Added integration tests for stdio MCP server using child process communication
packages/mcp/package.json	Added tinyexec dev dependency for process spawning in tests
tsconfig.json	Added es2024 lib for Promise.withResolvers() support
pnpm-lock.yaml	Lockfile updates for new dependencies and eval experiment artifacts
.changeset/heavy-towns-beam.md	Changeset documenting the patch

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported

[codecov]

Bundle Report

Changes will increase total bundle size by 432 bytes (1.13%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
@storybook/mcp-esm	21.08kB	432 bytes (2.09%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: @storybook/mcp-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
index.js	280 bytes	13.73kB	2.08%
index.d.ts	152 bytes	7.35kB	2.11%

Files in index.js:

• ./src/types.ts → Total Size: 756 bytes

• ./src/utils/get-manifest.ts → Total Size: 3.65kB

• ./package.json → Total Size: 221 bytes

[JReinhold]

@shilman confirmed that this fixed the evals. Self-merging