Coding (Platform)

Fastify: Plan migration batches for metrics hook data migration

A service boundary accepts valid traffic but mishandles duplicate, stale, or unauthorized records. The affected area is metrics hook.

Repair the metrics hook data migration implementation so it selects safe work under row and risk capacity while explaining skipped candidates.

Evidence

Affected surface: Fastify / metrics hook.
Observed failure family: plan migration batches.
Scope policy: zoneState must equal healthy.

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 hard 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.