Constant EOF_PENDING_DRAIN_GRACE 

const EOF_PENDING_DRAIN_GRACE: Duration;

One-shot stdio clients commonly write initialize + tool call JSONL and then close stdin. rmcp treats stdin EOF as service shutdown and starts draining in-flight responses with its own short timeout; slow backend tools can lose their result before the response is written. Keep EOF hidden from rmcp until requests already accepted by this transport either respond or this guard expires. Normal persistent MCP clients never hit this path.