An install from v2026.3.12 ships `.env` with `LLM_MODEL` set, because that
release's template wrote it. The upgrade runs config migration 12 -> 13, which
clears that dead var -- and the user-state verifier reported the change as the
upgrade modifying the user's own state, failing the leg.
The verifier exists to catch an upgrade taking state away; a var the CURRENT
tree retires is not that. The retired set is parsed out of
`hermes_cli/config_migrations.py` (the `for dead in (...): save_env_value(dead,
"")` shape) rather than restated here, so it cannot drift from the tree, and an
unreadable source retires nothing -- every .env change stays fatal.
Tolerance is deliberately narrow: only keys the tree retires, only when the
upgrade EMPTIED them, and only when no key was added or removed. Clearing a
live key, or deleting a retired one outright, still fails.
498725ae59