pub fn migrate_legacy_layout() -> Result<usize, ConfigError>Expand description
One-time best-effort migration of a pre-nesting flat layout
(~/.rpi/{auth.json,models.json,.setup_done,.earendil_seen}) into the
nested ~/.rpi/agent/ layout. No-op when RPI_CODING_AGENT_DIR is set
(never touch an explicit override), when the agent dir already exists, or
when no flat files are present. Idempotent: a partial move resumes. Errors
are swallowed (logged via the returned Result only so tests can observe);
app::run ignores them so a migration hiccup never blocks startup.