Attachment protocol mismatch

In both EJB client and server code, on method invocations where context data is sent, the sender writes the attachment count as a packed integer but the reader consumes it as an unsigned byte. This is not good.

The fix:

• In protocol 3 and higher, always read and write a packed integer
• In protocol 2 and lower, always read a packed integer but write a signed byte, failing if more than 127 attachments are present