Sessions and subagents

One session is one token entry. Long sessions move between branches, so they are split into segments, and subagents are placed on their own signals.

Segments

A session that changes branch or working directory is split into segments. Each segment is placed on its own, so one morning's session can post to two tickets.

Measured per message

Cost is measured per message, not per session. That is how segments split exactly, and how telemetry and bills join token entries: by message and request IDs.

Subagents

A subagent is placed on its own signals when it has them, such as a review subagent on a pull request. Otherwise it follows the session that started it.