vCon Agent Session

This document defines an "agent_session" extension for Virtualized Conversations (vCon) that profiles the use of vCon parties, dialog, analysis, and attachments to carry the record of an autonomous AI agent's internal session - its prompts, tool invocations, tool results, reasoning, and file or artifact provenance - alongside the human-facing conversation that the agent participated in or acted upon. The extension is a Compatible vCon extension. It introduces no new top-level fields and does not alter the semantics of existing ones. Instead, it specifies (a) how an autonomous agent is represented as a vCon party, (b) how agent message turns are placed in the dialog array, (c) how the internal agent trace (tool calls, results, reasoning, system events) is carried as a structured analysis entry whose body conforms to the Verifiable Agent Conversations (VAC) CDDL schema [I-D.draft-birkholz-verifiable-agent-conversations], and (d) how files and artifacts modified by the agent are carried as attachments. By projecting agent-session data into the vCon model, implementations inherit vCon's party/identity model, the lawful basis framework [I-D.draft-howe-vcon-lawful-basis], the lifecycle and redaction machinery [I-D.draft-howe-vcon-lifecycle], and JWS-based signing, without re-specifying any of those concerns.