portless mcp advertises 2025-03-26 but never answers a JSON-RPC batch

Summary

portless mcp accepts protocol version 2025-03-26. That version of the spec requires servers to support JSON-RPC batches, but when a batch arrives the server sends nothing back, so the client waits forever for those request IDs.

Reproduction (portless 0.15.12)

{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"t","version":"1"}}}
[{"jsonrpc":"2.0","id":2,"method":"ping"},{"jsonrpc":"2.0","id":3,"method":"tools/list"}]
{"jsonrpc":"2.0","id":4,"method":"ping"}

The server answers id 1 and id 4. It never answers id 2 or id 3.

Cause

handleLine returns null for any message that isn't an object (mcp.ts, if (!isObject(message)) return null), so an array is dropped without a response.

Expected

Either handle the batch and reply with an array of responses, or stop advertising 2025-03-26 and return an error for a batch. Batching was removed in 2025-06-18, so after that change the server would negotiate only versions that don't include it.