Board defaults represent persistent project checkouts. Scratch workspaces
are auto-deleted on completion and must stay under the per-board scratch
root that resolve_workspace() creates. Inheriting default_workdir for a
scratch task pointed the cleanup path at the user's source tree — the
data-loss vector documented in #28818.
The containment guard in _cleanup_workspace (just added) is the safety
rail. This commit prevents the bad state from being created in the first
place: only persistent kinds (dir/worktree) inherit board defaults.
Tests updated to cover the new semantics: scratch with default_workdir
set keeps workspace_path=None; dir/worktree still inherits the board
default.
Salvaged from PR #31315 by @leeseoki0 — prevention layer on top of the
#28819 containment fix by @briandevans.
Co-authored-by: teknium1 <127238744+teknium1@users.noreply.github.com>
ce529d6072