Coding (Platform)

NestJS: Validate state transitions for billing module lifecycle transitions

An operational alert points to a contract bug that appears only under mixed production data. The affected area is billing module.

Repair the billing module lifecycle transitions implementation so it accepts only declared state transitions and reports rejected requests.

Evidence

Affected surface: NestJS / billing module.
Observed failure family: validate state transitions.
Scope policy: tenantId must equal tenant-primary.

What this task practices

This coding (platform) exercise trains the same sequence expected in an interview: understand the prompt, make assumptions explicit, produce a concrete answer, and explain the decisions behind it. The task is marked easy difficulty. The private workspace adds the tools required by this round, such as recording, code execution, diagrams, evidence panels, or structured notes. It also preserves the attempt so later feedback can be compared with previous work. Evaluation is based on task-specific criteria and the candidate seniority selected in the preparation path. Public pages never expose the reference solution, hidden tests, evaluator instructions, or another candidate’s work.