Software-Engineering
Designing the push-notification service: idempotency keys as mandatory input, durable in-app records before OS push, fail-open preferences, receipt reconciliation, and WebSocket auth via subprotocol.
Software-Engineering
An in-process cron scheduler with a generation token, a promise lock, and soft-delete reconciliation — plus the drift panel that turns destructive sync into a recoverable operation.
Software-Engineering
Designing an Express + Better Auth service where deactivated users cannot sign in even when the database is down, tokens die on role change, and audit logging can never block a login.
