Each branch is a top-level conversation forked from another at an entry;
the session-scoped p2.main document lists them and names the current one.
Earlier branches are read-only. The main agent's per-agent state
(subagents, artifacts, voice and chat mode, pending move) stays on
conversation 1 for every branch.
- tree plugin: SessionTree (tree, navigate, select); the worker reports
main and branches to the catalog (Sessions v4, catalog schema 4)
- TUI: /tree and double Escape (pi's default "tree"), a tree selector
adapted from coding-agent
- web: Edit on user messages, Branch from here on answers, branch rows
under the session in the sidebar
- main-agent checks use the branch list instead of conversation 1
- search indexes each branch's own entries
Design: apps/p2/docs/tree.md
