Session Handoff [auto-1790]: Name the Leftover Old Tree When the Bash Loader Cannot Remove It per #1790 #2217

Next steps, in priority order

1. Fix Name the Leftover Old Tree When the Bash Loader Cannot Remove It #1790. In host-setup/bootstrap.sh, swap_in calls remove_owned "$retired" bare before moving the live tree aside. When an owned skills-tree.old holds an entry rm cannot remove, remove_tree fails, set -e aborts, and the loader prints only rm's own error. Give bash the refusal bootstrap.ps1 already gives in the same state, naming the leftover path and the remedy (close what holds it, or remove it by hand, then run again), so the run stops with the loader's own message. Done looks like: the bash loader stops with a message naming the .old path in that state, the PowerShell loader is unchanged or brought to the same wording only where it differs, and a test or constructed reproduction shows the message, with the fix reverted to prove the test fails without it.
2. Drive the pull request to develop with its body carrying Closes on promotion: #1790, then close this lane out.

External blockers

None known.

Internal dependencies

None. #1795 (empty-directory leftover after the final removal) and #1792 (locking the bootstrap directory) touch the same file and are related, but neither is part of this lane, so do not fold them in.

State

No branch, worktree, or pull request exists yet. PR #1794 (merged) touched the same functions and named #1790 as not addressed. Re-derive the current swap_in and remove_owned from origin/develop rather than from this text.

The parked decision queue

Zero parked decisions.

What the last round did

The unattended picker created this lane from the open backlog. Nothing has been changed.

What not to repeat

Nothing yet.

New learnings

None.