One message per line

Your server is a persistent process. Read stdin line by line, parse every non-empty line as a JSON object, and write exactly one compact response per request.

At this stage accept {"jsonrpc":"2.0","id":1,"method":"ping"} and answer {"jsonrpc":"2.0","id":1,"result":{}}. Preserve the id without turning numbers into strings. Do not print diagnostics to stdout.

Keep transport, method dispatch, and response construction separate. You will reuse all three later.

• Process every message until EOF.
• ping returns an empty result.
• Each response ends in a newline and contains no extra spaces.