Defense-in-depth fix for the silent wipe of ~/.hermes/ documented in
#48200. A `hermes update --yes` run silently destroyed a user's
.env, MEMORY.md, kanban.db, custom skills, and scripts. Two changes:
1. `_rmtree_writable` in tools/skills_sync.py now refuses to rmtree
anything outside SKILLS_DIR (the HERMES_HOME/skills/ root).
All five call sites pass paths under SKILLS_DIR, so the guard is
a no-op for current code and a loud, recoverable failure for
any future regression (bad path join, malicious bundled
manifest, stale path in scope after an exception).
2. The default `updates.pre_update_backup` flips from false to
true in hermes_cli/config.py. A few minutes of zip per update
is negligible compared to silent total data loss. Still
overridable; --no-backup still works for one-off opt-out.
Five new tests in TestRmtreeWritableScopeGuard (root path,
hermes home, sibling dir, skills root itself, subdir) plus a
flipped `test_default_enabled_creates_backup` in test_backup.py.
178/178 tests pass in the two affected files. Public method
signatures unchanged, no test-stub blast radius.
Closes#48200
f1254c8eaf