fix(happy-cli): create fresh MCP server+transport per request for SDK >=1.26 compat

[nikhilsitaram]

Summary

• Fixes MCP tool calls failing after the first invocation due to stateless transport reuse
• Creates a fresh McpServer + StreamableHTTPServerTransport per HTTP request instead of sharing a single instance

Problem

MCP SDK v1.26.0 introduced a restriction that stateless transports (sessionIdGenerator: undefined) cannot be reused across requests. The previous code created one McpServer and one StreamableHTTPServerTransport at startup and reused them for all requests:

// Before: single shared transport
const transport = new StreamableHTTPServerTransport({
    sessionIdGenerator: undefined
});
await mcp.connect(transport);

const server = createServer(async (req, res) => {
    await transport.handleRequest(req, res);  // fails on 2nd call
});

The first tool call (e.g., mcp__happy__change_title) succeeds, but all subsequent calls fail with "Stateless transport cannot be reused".

Fix

Factory pattern — each request gets its own server+transport pair, cleaned up on connection close:

const server = createServer(async (req, res) => {
    const mcp = createMcpServer();  // fresh server with tools registered
    const transport = new StreamableHTTPServerTransport({
        sessionIdGenerator: undefined
    });
    await mcp.connect(transport);
    await transport.handleRequest(req, res);
    res.on('close', () => {
        transport.close();
        mcp.close();
    });
});

Test plan

• Verify mcp__happy__change_title works on first call
• Verify mcp__happy__change_title works on second and subsequent calls within the same session
• Verify transport/server cleanup occurs after each request (no resource leaks)

🤖 Generated with Claude Code