AGTP Session Protocol

This document specifies the AGTP Session Protocol (AGTP-SESSION), a companion to [AGTP] that defines session semantics for agent-to-agent and agent-to-API communication. AGTP-SESSION addresses two distinct session models: bounded sessions for time-limited transactional flows, and persistent sessions for long-lived agent contexts. Both inherit identity, authority, and attribution from base AGTP. This is an early working draft; many design decisions are deliberately open.