Proxy MCP client name in local stdio server User-Agent

[mvanhorn]

Summary

Extracts the MCP client name from the initialize request and includes it in the User-Agent header sent to mcp.stripe.com. When Cursor connects, the header reads stripe-mcp-local/0.3.1 (cursor) instead of the static stripe-mcp-local/0.3.1.

Changes

• Deferred HTTP transport creation: The HTTP transport is now created on the first stdio message instead of upfront. This lets us inspect the initialize message for clientInfo.name before building headers.
• extractClientName(): Parses a JSONRPCMessage and returns the client name if the message is an initialize request with clientInfo.
• buildUserAgent(): Appends the client name in parentheses to the base user agent string.
• Tests: 6 new test cases covering client name extraction (Cursor, Claude Desktop, missing clientInfo, non-initialize messages, responses, notifications) and User-Agent formatting.

All messages are still forwarded unchanged - the proxy only peeks at the first message for metadata.

Testing

All CI checks pass locally:

• pnpm run build - clean
• pnpm run lint - clean
• pnpm run prettier-check - clean
• pnpm run test - 17/17 passing (6 new + 11 existing)

Fixes #250

This contribution was developed with AI assistance (Claude Code).

[cla-assistant]

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