A blank Variant Position cell previewed position->null and aborted the
confirm transaction (variant.position is NOT NULL). Resolve the clear to
the variant's file order at diff time so preview and apply stay in
lockstep; carry file_order on VariantPlan instead of an identity-keyed
map; release the read snapshot before PreviewStale/NothingToApply.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
ben.stull