Function apply 

pub fn apply(
    store: &LocalFsStore,
    flags: &OpFlags,
    target: &str,
    state_dir_override: Option<&Path>,
) -> Result<OpOutcome, OpError>

op env migrate-state <env_id> --apply. Re-runs the check, refuses with OpError::Conflict if not clean, then renames <state_dir>/deploy/ to a hidden .deploy-migrated-<ts> sentinel under the same parent.

Idempotent: if no legacy tree exists, returns a no-op outcome with legacy_dir_renamed_to: None.