When a pane starts a turn (agent.working not from blocked), snapshot the
workspace checkout into a tree through a private index copy and keep it
as the workspace's latest turn baseline. workspace.diff and
workspace.file_diff accept scope "turn" and compare that tree with a
fresh one, so work the agent committed during the turn stays visible.
A capture emits workspace.turn_started.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>