Fix built-in MCP startup failures and remove deprecated Puppeteer server

[elliottophellia]

Summary

Fix built-in MCP servers failing during initialization with errors such as:

initialize: mcp error 0: EOF

The EOF hid the actual problem: several MCP child processes exited before replying because their package or MCP SDK versions were incompatible.

Why Puppeteer was removed

The built-in Puppeteer entry used @modelcontextprotocol/server-puppeteer, which npm marks as deprecated and no longer supported.

During end-to-end testing, the server also failed to complete the MCP initialization handshake before the client timeout, even after installing its required browser artifacts. Keeping it in the built-in catalog would advertise a server that is unsupported and does not reliably start.

Antares already provides two maintained alternatives:

• Its native browser tool for normal browser automation.
• The Playwright MCP server for users who specifically need an external browser MCP.

Removing Puppeteer avoids presenting a known-broken, deprecated option while preserving equivalent browser automation capabilities.

Changes

• Pin compatible package and MCP SDK versions for built-in servers.
• Expand ${HOME}, environment variables, and ~/ in stdio arguments.
• Report child-process exit status and stderr instead of generic EOF errors.
• Automatically migrate unchanged legacy built-in configurations to pinned definitions.
• Update Linear and Sentry to their current Streamable HTTP endpoints.
• Remove the deprecated and non-starting Puppeteer MCP entry.
• Preserve custom MCP commands and arguments.
• Add regression tests for startup diagnostics, argument expansion, and legacy configuration migration.

Verification

All remaining local built-in MCP servers completed initialization and tool discovery:

• Filesystem
• Fetch
• Git
• PostgreSQL
• SQLite
• Memory
• Sequential Thinking
• Time
• Slack
• Brave Search
• Notion
• Playwright
• Everything

Checks passed:

go test ./internal/mcp ./internal/hub ./internal/server -count=1
go vet ./internal/mcp ./internal/hub
go build ./cmd/antares

Credential-backed servers were initialized with placeholder credentials to verify startup and tool discovery. Authenticated API operations were not exercised.