The password file was stored at agent_notes_dir/matrix-password which
lives inside agent_state_root — wiped by destroy --purge. On re-spawn
with the same agent name, the matrix user still exists in the homeserver
but the stored password is gone, making re-login impossible.
Move password to /var/lib/hyperhive/matrix-creds/<name>-password which
is not deleted by purge. On re-spawn, ensure_user_for finds M_USER_IN_USE,
reads the preserved password, re-logins, and writes a fresh token.
Also:
- add one-time migration that moves existing passwords from the old path
to the new location on first access after upgrade
- remove chown_to_agent on the password file (it is now host-only, not
inside the agent bind-mount tree)
- fix the error message to give actionable recovery steps instead of
suggesting hivectl matrix create-user --password which is rejected for
agent accounts
47e9c1cc1b