'always' — bound in every condition evaluation, derived from the
instance and its snapshot.
'caller' — rides the acting caller; without one the var is undefined
(conditions referencing it fail closed). Author predicates may not read
these — they pre-evaluate caller-free, per evaluation context.
'spawn' — bound only at spawn sites (the per-row $row).
When a condition var holds a value:
'always'— bound in every condition evaluation, derived from the instance and its snapshot.'caller'— rides the acting caller; without one the var isundefined(conditions referencing it fail closed). Author predicates may not read these — they pre-evaluate caller-free, per evaluation context.'spawn'— bound only at spawn sites (the per-row$row).