The native client replays its offline outbox with the same
Idempotency-Key on every attempt, and `POST /api/medications`, the
side-effect log and the inventory register ran the handler again on the
replay: after a lost success response the account was left with a
duplicate medication, a duplicate symptom entry or a second pen in the
supply count. The dedupe on `(externalSource, externalId)` only ever
covered a MIRRORED create; a manually entered medication carries
neither field and had nothing to collapse a retry onto.
All three wrap in `withIdempotency`, the composition the batch ingest
already ships, and the three operations publish the header so a client
generated against the contract can tell that a retry is safe. Zod
parsing and `requireRecordAuth` are untouched.
An integration test drives each route twice against real Postgres and
asserts what a status check cannot: one row in the table, and a replayed
201 carrying `X-Idempotent-Replay: true`.
