Heavy MCP servers (FastMCP with 80+ tools, OAuth servers) take 3-5s to
start their stdin read loop. Without retries, connectAndDiscover sends
the initialize request immediately after fork/exec, gets EOF, and
permanently fails with "transport closed".
Add a retry loop (4 attempts, 2s/4s/8s backoff) for stdio transports
only. SSE/HTTP transports fail immediately since connection-refused is
definitive. The retry respects context cancellation to avoid blocking
shutdown.
Closes#385