- a changed group definition no longer runs dbDelta on an existing table
inside a web request (seconds to minutes on a large table, and every
concurrent request tried it): the group is recorded in tmdo_schema_deferred
and tmdo_ensure_group_indexes is scheduled, whose request upgrades it
- meanwhile the group stays native: Hook Bus field lookups return no field and
the router treats it as drifting; afterwards a drift fix
(tmdo_drift_resync) rebuilds the writes that skipped the flat table
- new tables are still created at once; aeav_only upgrades at once (the flat
table is the only copy); doctor lists deferred groups
- Verify: SchemaUpgradeDeferralTest, Hook Bus and router tests, integration
582, unit 701, phpcs, stan; dev36 live cycle in the 2.3 acceptance
- PR: PR-107
