Backend half of offline Phase 1. Lets the offline outbox replay a write after a
lost response without executing it twice (e.g. an order whose POST reached the
server but whose reply never came back).
- IdempotencyRecord entity + table (unique index on (Scope, Key)); migration
AddIdempotencyRecords. Standalone POCO — no tenant/soft-delete filters.
- IdempotencyMiddleware (after TenantMiddleware, before plan-limit/controllers):
opt-in via `Idempotency-Key` header on POST/PUT/PATCH/DELETE.
* Completed key → replays stored status+body with `Idempotent-Replay: true`.
* In-progress key → 409 IDEMPOTENCY_IN_PROGRESS; the unique index serializes
racing first requests; stale (>60s) reservations are recovered after a crash.
* Only <500 responses are cached; 5xx is released so the client can retry.
Bookkeeping runs in isolated DI scopes so it never contaminates the controller's
unit of work. Keys are scoped per café — no cross-tenant collisions.
- 5 middleware tests (replay/execute-once, distinct key, pass-through, tenant
isolation, 5xx-not-cached). Full suite 86 passing.
Next in Phase 1: generalize the POS order queue into a generic client outbox that
sends these keys and remaps client→server ids.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
soroush.asadi
f4583f5169