`medication_intake_events.idempotency_key` carried a GLOBAL unique from
0001_init. The value is client-supplied, so two people running the same
client can mint the same key — and on a global unique the second one is
simply refused by the constraint. Their dose is not written and nothing
tells them so. The bulk drain made it worse: its replay probe read the
key with no user scope, resolved the first user's row, and reported the
second user's entry as a duplicate carrying a stranger's row id.
Migration 0273 replaces the global unique with `(user_id,
idempotency_key)`, the grain every other client-supplied identity on the
table already uses. Both unscoped reads in the bulk drain now key on the
composite; the other four reads were already narrowed by user.
On existing data this is a relaxation, so nothing needs reconciling: the
old constraint is strictly stronger than the new one, and no pair of rows
can violate an index the previous one already forbade. The migration
still carries a reconciliation step for a database whose global index was
dropped by hand at some point. It never deletes or rewrites a dose — it
clears the dedup HINT on the later row of a colliding pair and keeps
every intake event, timestamp, attribution and inventory stamp intact.
The new index is created before the old one is dropped, so a failure
aborts with the old protection still in place.
A structural guard freezes the read side: no `medicationIntakeEvent`
query may filter on the key without narrowing by `userId`.
Marc-André Bombeck
18691d4550