Why: git refuses to remove a worktree with initialized submodules; the first
real dogfood run of task-finish hit this on the empty-list fix task.
Evidence: the fix task's worktree recycled only after manual force-remove;
deinit-then-remove path exercised on the same state afterwards.
Impact: finish deinitializes submodules, removes, prunes, and deletes the
remote branch; unmerged-result guard unchanged.
Refs: .task/fix-empty-list-json.md
weichen