Review of #130067: traits described kernel meaning nothing reads (and two
descriptions were incomplete: archived also satisfies a parent gate; the
kernel re-checks parents on ready/review). Same reasoning as the dropped
event model: Phase 0 keeps only data that is consumed or checked against
live code; column semantics are designed with the kernel switch.
Nits: VALID_STATUSES is the frozenset itself; precise tuple/frozenset types.
c950e2278d