Functional requirements (FR)

• Create and manage the primary transaction or listing lifecycle from initiation through completion or cancellation.
• Support lookup of current status, transaction history, and the parties or items involved.
• Apply domain rules for pricing, eligibility, inventory, settlement, or auction outcomes as stated in the prompt.
• Provide auditable records for user actions and externally visible state changes.

Non-functional requirements (NFR)

• Prevent duplicate or conflicting transactions under retries and concurrent requests; define the required consistency boundary.
• Protect account, payment, and transaction data with authentication, authorization, encryption, and auditable access.
• Set explicit latency and availability targets for read and write paths, including degraded operation during dependency failures.
• Define reconciliation, recovery, and retention objectives for financial or order records.

Principal-level discussion

• Define the scale, success measures, and operational ownership before committing to an architecture.
• Compare at least two viable approaches and explain the trade-offs, migration path, and failure behavior.
• Identify the riskiest assumptions and how you would validate them with data or a staged rollout.