Use Case Specifications: User Account System

Problem/Feature Description

Your team has just completed the requirements phase for a new user account system. The product owner has signed off on the requirements catalog at docs/requirements.md and a high-level use case diagram at docs/use_cases.puml that captures two core flows: account registration and login.

The engineering team is now ready to begin implementation, but they need detailed use case specifications before writing any code. The specifications will serve as the contract between the business and the development team — they must cover both the happy path and the various ways things can go wrong, so that everyone from stakeholders to developers can agree on exactly how each interaction should behave.

Output Specification

Write complete use case specification documents for all use cases shown in docs/use_cases.puml. Place the files in the docs/use_cases/ directory, with one file per use case.

For each use case, the specification must cover: a complete overview section, preconditions, a fully numbered main success scenario, alternative flows for the meaningful error and edge cases, success and failure postconditions, and any relevant business rules.