Function plan 

pub fn plan(
    desired: &DesiredTable,
    current: Option<&TableState>,
    opts: ReconcileOptions,
) -> ReconcilePlan

Compute the plan to reconcile desired against current (the live table, or None if it does not exist yet).

Pure and deterministic: no I/O, no clock, no randomness. The same inputs always produce the same plan, so a backend can log it before executing and a test can assert on it without a catalog.