Expose an event's prechange and postchange snapshots to event rule
condition evaluation, making snapshots.prechange.<attr> and
snapshots.postchange.<attr> available through the existing dot-path
syntax.
Add changed and unchanged snapshot operators for comparing an attribute
across the two snapshots without requiring a condition value. These
operators support rules such as firing only when a field transitions to a
specific state.
Make condition values optional only for snapshot operators by introducing
a missing-value sentinel, while preserving value requirements for all
other operators. Reject invalid combinations such as using changed or
unchanged with an explicit value or with an attr starting with snapshots.
Fail closed when condition paths traverse invalid snapshot structures,
including raw scalar snapshot values such as status strings, by treating
unresolvable snapshot-operator paths as missing and converting invalid
direct paths to InvalidCondition.
Document the new snapshot path syntax, changed and unchanged operators,
create/delete snapshot behavior, and the serialization differences
between snapshot data and REST API data. Add regression and integration
tests covering validation, transition behavior, null snapshot edge cases,
direct snapshot paths, and event rule evaluation.
d88b6a65dd