The local/worktree choice was unstored component state and reset on every
remount of the New Workspace screen (e.g. after creating a workspace).
Persist it in the create-form preferences (FormPreferences.isolation).
Also rename the app-layer "backing" to "isolation" to match its UI label.
Isolation is the create-time intent; it stays distinct from workspaceKind,
the git-derived persisted property, and the wire's source.kind.
Multiple workspaces can share one checkout directory. Agent and terminal
status, sidebar tabs, and ownership now attribute strictly by workspace ID,
so a running or blocked agent in one workspace no longer shows up on its
same-directory siblings.
A one-time startup migration backfills workspace IDs onto legacy agents, and
every agent and terminal is created with one thereafter. Directory lookups
remain only for genuinely folder-derived git facts (branch, diff) and the
archive-by-path adapter.
Mohamed Boudra