Direct intershard communication
Shards used to talk through a middleman. Masterchain. Every message: wait for commit, wait for confirmation, wait again. Two shards chatting? Add a second of masterchain delay. Per hop. Shards now read directly from each other. Dependency resolution algorithm keeps everything consistent. Same security guarantees. No waiting for masterchain permission.
2 shards or 256 — same speed. Latency stays constant.