Branches of a file in a live session: create, edit, review, update from
main and merge while the file is in a session. The branch stays with its
author and makes ids in their own client space far above the main file's;
merging is one synced edit and one undo step; peers' edits merge against
the branch's own base and conflicts resolve as offline; a view link still
refuses merging; a branch made outside the session that adds layers is
refused with a reason. Branch history entries for creation and updates
from main. Fuzz and junk tests extended to export settings, guides and the
live case. Docs: gap 17, collaboration parity, ROADMAP, mcp, protocol.